Basic Rad Phy1

Page Phy-1 January 2006 Principles of Radiation Protection Section 1 - Basic Radiation Physics

Section 1

BASIC RADIATION PHYSICS

UW Environmental Health and Safety

Page Phy-3 January 2006 Principles of Radiation Protection Section 1 – Basic Radiation Physics

The object of this section is to provide the fundamental concepts of physics that are necessary to understand radioactive decay, radiation, and the interaction of radiation with matter. These concepts will be brought together to allow an understanding of the physical measurement of radioactivity, exposure, and absorbed dose. Some information is also provided to describe the natural background radiation environment. A. Atomic and Nuclear Structure

1. Basic Atom

The atom is the smallest unit of matter that retains the chemical properties of an element. Atoms consist of a nucleus and orbital electrons. The nucleus is a heavy central mass with a positive charge. The nucleus accounts for most of the mass of an atom, but is small in diameter compared to the overall size of the atom. Particles within the nucleus are known as nucleons. Outside the nucleus is a cloud of electrons - small, negatively charged particles that are attracted to the atom by the opposing charge of the nucleus (coulomb forces).

2. Protons and Neutrons (Nucleons)

The nucleus is composed of protons and neutrons. Protons have a positive (+ 1) charge with a mass of about 1.007 atomic mass units (1.673 x 10-24 grams). Neutrons are neutral, or uncharged. Neutrons have a mass slightly larger than the proton, about 1.008 atomic mass units (1.675 x 10-24 grams). Although the coulomb forces between protons in the nucleus tend to push the nucleus apart, the nucleus is held together by the strong nuclear force that operates at extremely short distances. The strong nuclear force is believed to result from attractions between even smaller particles (quarks) that compose the neutrons and protons.

3. Electrons

The charge of the electron (- 1) is equal in magnitude to the charge of the proton but is negative instead of positive. In an uncharged atom, the number of orbital electrons equals the number of protons within the nucleus. When the number of orbital electrons does not equal the number of protons in the nucleus, an overall imbalance of charge exists for the atom. A charged atom is known as an ion. Ions readily form chemical bonds with other ions of opposing charge. Although electrons exist in a cloud around the nucleus, it is useful to describe this arrangement as a series of energy levels, called shells. Within each shell are subgroups of electrons, called orbits. An atom may have a number of possible energy states, which correspond to different arrangements of electrons in the shells. Electrons normally occupy the lowest energy levels in the atom, with successive shells and orbits filled in a complex manner. If an atom absorbs energy, an electron can move to a higher-energy shell. Electrons occupying higher


Page Phy-4 January 2006 Section 1 – Basic Radiation Physics Principles of Radiation Protection

energy levels can move back to vacancies in lower energy levels by releasing energy. When the energy release is small (such as for transitions between outer shells of an atom), the release occurs as visible or ultraviolet light. When the difference in energy levels is large (such as when an electron moves to an inner shell), an x-ray is emitted.

4. Atomic Number, and Atomic Mass Number

The number of protons in the nucleus of an atom is known as the atomic number, and is represented by the symbol Z. The number of protons in the nucleus determines the arrangement of the electron shells for that atom, which accounts for most chemical characteristics associated with the atom. Therefore, atoms are grouped into elements according to their atomic number. Each element is also represented by a chemical name. The total number of protons and neutrons in the nucleus of an atom is called the atomic mass number (or, mass number). The symbol A is used to denote the atomic mass number. Since atoms do not have “fractions” of protons or neutrons, the atomic mass number is an integer. The atomic mass number should not be confused with the atomic mass. Atomic mass describes the relative mass of the atom (including orbital electrons). The scale for atomic mass is fixed so that it equals 12.000 amu for an atom having 6 protons, 6 neutrons and 6 electrons. This atom (Carbon-12) also has an atomic mass number of 12. For all other atoms, the atomic mass and atomic mass numbers differ slightly in magnitude. The number of neutrons in an atom is called the neutron number and is represented by the symbol N. Table 1 illustrates the relation of A, Z and N for several atoms.

Table 1 – Examples of Z, N, and A

Atomic No. Z (Protons)

Neutron No. N (Neutrons)

Mass No. A (Nucleons)

Hydrogen-1 1 0 1

Carbon-12 6 6 12

Iron-56 26 30 56

5. Nomenclature

Standard nomenclature is used to identify atoms of different types. The chemical



symbol for the element is written with an upper left superscript before the symbol, indicating the mass number (A). A lower left subscript before the symbol indicates the atomic number (Z). This is illustrated by the examples from table 1:

Hydrogen-1 11H

Carbon-12 6

12C Iron-56 26

56Fe

Since both the atomic number and the chemical symbol uniquely identify the element, it is acceptable to omit the atomic number. The designation of an atom is often simply the chemical symbol followed by the atomic mass number, e.g. H-1, C-12, Fe-56.

6. Nuclides, Isotopes, Isobars

It is convenient to classify atoms by similarities with other atoms. The term nuclide is the most general term that describes an atom. Any atom can be referred to as a nuclide, without making any implications about element groupings or other properties of that atom. As stated earlier, an element is a group of nuclides with the same number of protons. However, there can be different numbers of neutrons present in the nucleus for atoms of the same element. Atoms that have the same number of protons but different numbers of neutrons are called isotopes of that element. This is illustrated for the three isotopes of the element hydrogen:

Hydrogen-1 (1 proton, 0 neutrons, A=1) 11H

Hydrogen-2 (1 proton, 1 neutron, A=2) 1

2 H Hydrogen-3 (1 proton, 2 neutrons, A=3) 1

3H

Isobars are defined as nuclides having the same mass number (A) but different atomic numbers (Z). Example: I-131, Te-131 and Se-131 are isobars. This term is rarely used.

7. Energy Units

The energies involved for individual reactions at the atomic level are small compared to everyday electrical and mechanical processes requiring huge numbers of atoms. The unit of energy used most frequently in atomic physics is the electron volt, or eV. An electron volt is defined as the amount of energy acquired by an electron when it falls through a difference in potential of 1 volt.



The eV unit is often used with a multiplier, either keV or MeV; 1 keV is equal to 1,000 eV, (1 keV = 103 eV) and 1 MeV is equal to a million eV, (1 MeV = 106 eV). If it were possible to instantly turn on a light bulb, 1 MeV of energy would operate a 100 watt light bulb for a duration of only 1.6 x 10-15 seconds. Most nuclear interactions involve tens of keV up to several MeV of energy.

B. Radioactive Decay 1. General

Radioactive decay is the process in which an unstable atom releases matter and/or energy during a transition to a more stable form. It may do so by releasing subatomic particles and energy, or by capturing an orbital electron into the nucleus and releasing energy. Atoms that are unstable are also known as radioactive atoms, or radionuclides. The original, radioactive atom is known as the parent. The new nucleus (after decay) is known as the daughter. Radioactive decay has applications in research, cancer therapy and medical imaging because some of the stable atoms in drugs, reagents, or antibodies can be replaced with radioactive atoms. The resulting “labeled” form has the same chemical characteristics as the nonradioactive form. Depending upon the application, the outcome of a chemical reaction can be traced, radiation can be delivered to tumors, and structures in the body can be imaged through release of radiation (in a medical setting).

2. Stability and Instability

The nucleus of an atom exists because the attractive force (strong nuclear force) operating among protons and neutrons balances the coulomb force pushing the nucleus apart. Some combinations of neutrons and protons are very successful in holding the nucleus together. These nuclides remain intact indefinitely and are said to be stable. For other atoms, the numbers of nucleons are less favorable and the atom is unstable (radioactive).

To observe the pattern of stability among nuclides, the stable nuclides can be plotted on a graph with the vertical axis indicating the N value (number of neutrons) and the horizontal axis representing the Z value (number of protons). This chart is shown in Appendix 1, Figure 1. These nuclides “cluster” in a small area of the graph, indicating conditions that are favorable for stability. The rules of stability are complex. Some of the factors influencing stability include:

• The mass of the atom. • The ratio of neutrons to protons.



• Even versus odd numbers of nucleons. • “Magic numbers” of nucleons (exceptionally stable combinations).

The optimum ratio of neutrons to protons varies from 1:1 for light nuclei to more than 1.5:1 for heavy nuclei. Atoms lacking these ratios are not stable. If an atom has an even number of protons and neutrons, it is more likely to be stable. Atoms are particularly likely to be stable if the number of protons and/or neutrons corresponds to one of the following integers: 20, 28, 50, 82 and 126. The region of stability ends with Bi-209; all nuclides heavier than bismuth are radioactive. Unstable atoms tend to decay in a manner that shifts the composition of the daughter nucleus towards a more favorable combination of nucleons. The direction of this shift determines the type of radioactive decay (this will be discussed in subsequent sections). Some radionuclides can achieve stability through a single decay (the daughter is stable). For other radionuclides, a series of decays must occur before stability is reached.

3. Rate of Decay

a. Decay Constant

The process of decay is random for individual atoms. Although the exact moment of an individual atomic decay cannot be predicted, the probability of decay during a given time period can be measured (based on observations from a large number of atoms). This quantity is known as the decay constant (λ). The decay constant is expressed in units of probability per unit time.

b. Half-Life (t½)

The rate of decay can also be described by the half-life of the atom. The half-life (t½) is the amount of time required for 50% of the parent atoms to undergo radioactive decay. The half-life and decay constant are related through the simple expressions:

λλ693.02ln

21 ==t

21

21

693.02lntt

==λ

Consider the case of a radionuclide with a very short half-life, sodium-25. This radionuclide has a half-life of 60 seconds. The decay constant equals (0.693)/60s, or 0.012s-1. An example of a longer-lived radionuclide is tritium



(H-3). Tritium has a half-life of 12.3 years. The corresponding decay constant is (0.693)/12.3y, or 0.056 y-1. If converted to seconds, the decay constant for tritium is 1.79 x 10-9 s-1.

c. Activity

It is easy to see that a radionuclide with a short half-life will undergo radioactive decay at a very rapid rate, while a radionuclide with a long half-life will have a much smaller rate of decay. If you have a sample of one billion (109) sodium-25 atoms, you would expect about 11 million of these to decay during the next second. On the other hand, if you have sample of one billion tritium atoms, you would expect only 1 or 2 of these atoms to decay during the next second.

For convenience, radioactivity is measured in units of activity, or the number of decays taking place each second. The traditional unit of activity is the curie, named after Marie and Pierre Curie (the discoverers of radium). One curie, abbreviated Ci, is equal to 3.7 x 1010 disintegrations per second (dps). Since this is an extremely large number of decays per second, the activity is usually expressed in smaller multiples:

1 x 10-6 Ci = 1 microcurie, or 1 x 10-3 Ci = 1 millicurie.

The International System of Units (Système International, or SI) utilizes a different unit of activity, the becquerel. One becquerel, or Bq, is equal to one dps. Since this amount of activity is inconveniently low, the SI units are normally expressed in large multiples of Bq (megabecquerel or gigabecquerel). The SI and traditional units are summarized in Table 2.

Table 2 – Units of Activity

Unit

Abbreviation

Multiple

Type of

Unit

Number of Disintegrations

per Second (dps) curie Ci 1 Ci Traditional 37,000,000,000

millicurie mCi 10-3 Ci Traditional 37,000,000 microcurie :Ci 10-6 Ci Traditional 37,000

nanocurie nCi 10-9 Ci Traditional 37

becquerel Bq 1 Bq SI 1

kilobecquerel kBq 103 Bq SI 1000 megabecquerel mBq 106 Bq SI 1,000,000

gigabecquerel gBq 109 Bq SI 1,000,000,000



Mathematically, the activity (A) is equal to the number of radioactive atoms (N) times the probability of decay (8):

λ⋅= NA

d. Exponential Decay

If the activity of a particular radionuclide is measured as a function of time, it can be seen that radioactive decay is exponential:

Stated as an equation:

⎟⎟⎟

⎠

⎞

⎜⎜⎜

⎝

⎛ ⋅−

⋅− ⋅=⋅= 21

693.0

)(t

t

ot

o eAeAtA λ

A(t) is the activity at time t, and A0 is the initial activity. Since the activity is proportional to the number of radioactive atoms, the equation can also be written:

⎟⎟⎟

⎠

⎞

⎜⎜⎜

⎝

⎛ ⋅−

⋅− ⋅=⋅= 21

693.0

)(t

t

ot

o eNeNtN λ

N(t) is the number of radioactive atoms at time t, and N0 is the initial number of radioactive atoms.



As an example, consider the decay of iodine-131. This radionuclide has a half-life of 8.05 days. If a sample contained 10 mCi on a particular date (as indicated by the supplier), what would the activity be one month later?

Initial Activity: A0 = 10 mCi

Elapsed time: t = 1 month Since the half-life is listed in days, convert elapsed time to days: t = 30 days Calculated decayed activity:

mCiemCieAtA daysdays

tt

o 76.0)10()( 05.830693.0693.0

21

=⋅=⋅=⎟⎟⎠

⎞⎜⎜⎝

⎛ ⋅−⎟

⎟⎟

⎠

⎞

⎜⎜⎜

⎝

⎛ ⋅−

The simple decay equation applies only when there is one radionuclide present. If there is a mixture of radionuclides present (as for a parent mixed with radioactive daughters), then a sum of exponential functions would apply.

4. Types of Radiation

a. Subatomic Particles

Some forms of ionizing radiation consist of subatomic particles ejected from the nucleus during radioactive decay. Examples of these subatomic particles are shown below in Table 3. It is useful to describe particulate radiation by the Greek letter symbols (alpha, beta) instead of by the particle name (helium nucleus, electron). This distinguishes the particles emitted during radioactive decay (which travel at high velocities) from subatomic particles which are bound within atomic or molecular structures.

Table 3 – Examples of Particulate Radiation

Type of Radiation

Greek Symbol

Description

Charge

Mass at Rest

Alpha α Combination of 2 protons and 2 neutrons

+2 4.001 amu (6.64 x 10-24 g)

Beta (-) −β Electron -1 0.000549 amu (9.11 x 10-28 g)

Positron, or Beta (+)

+β Positron (antimatter electron)

+1 0.000549 amu (9.11 x 10-28 g)



b. X-rays and Gamma Rays

Other types of radiation are electromagnetic. Electromagnetic radiation consists of packets of energy called photons (sometimes symbolized as νh ). X-rays and gamma rays are photons having enough energy to produce ionization. The use of two different names (x-rays and gamma rays) allows for a clearer distinction of where the photon was emitted. X-rays come from events occurring outside the nucleus of the atom. Gamma rays are emitted by the nuclei of unstable atoms after radioactive decay.

Several kinds of interactions may create x-rays. They are related to the energy balance (conservation of energy) that exists at the atomic level. For example, when an orbital electron moves from an outer (higher energy) shell to an inner (lower energy) shell, an x-ray must be emitted with an energy equal to the difference between energy levels. When an unbound electron traveling outside the atom suddenly slows down and changes direction (due to the presence of an adjacent atom), an x-ray is emitted with an energy equal to the decrease in electron energy.

5. Types of Radioactive Decay

a. Alpha ( )α Decay

Alpha decay tends to occur in heavy radionuclides (massive nuclei). The parent nucleus emits an alpha particle consisting of two protons and two neutrons (Z = 2, A = 4). This is identical to a He-4 nucleus. The identity of the daughter nucleus can be determined by subtracting 2 from the atomic number (Z) of the parent and 4 from the mass number (A) of the parent:

4

2

−=

−=

parentdaughter

parentdaughter

AA

ZZ

If the kinetic energy of the alpha particle is less than the energy released by the decay process, the daughter nucleus is left with excess energy. The extra energy is released in the form of one or more gamma rays. This occurs almost simultaneously with the alpha decay. An example of alpha decay is Ra-226:

MeVRnRa 59.54

222286

22688 ++→ ++α (parent) (daughter) (alpha particle) (energy released by decay process)

For Ra-226, the 5.59 MeV decay energy is released entirely to the alpha particle in 94.6% of all instances. In 5.4% of the decays, the decay energy is divided between a 5.40 MeV alpha particle and 0.19 MeV gamma ray.



b. Beta ( )−β Decay

Beta decay tends to occur when a nucleus has too many neutrons to achieve stability. During beta decay, a neutron within the parent nucleus is converted to a proton, an electron (e-) and a neutrino:

ν++→ −epn 11

10

(neutron) (proton) (electron) (neutrino) The proton remains in the daughter nucleus. The electron leaves the atom at a high velocity (as a beta particle). Because it is charged, a beta particle can interact and deposit energy in surrounding materials. The neutrino, however, is chargeless and nearly massless. For all practical purposes, the neutrino flies off into space without depositing energy or interacting with other atoms. The conversion of a neutron to a proton within the nucleus has the effect of increasing the atomic number (Z) by one while keeping the same atomic mass number (A). The loss of a slight amount of atomic mass does not change the value of A, since the daughter has the same number of nucleons as the parent.

parentdaughter

parentdaughter

AA

ZZ

=

+= 1

For any individual decay process, the beta energy may range from zero to the maximum beta decay energy (Emax). This happens because the beta particle randomly shares energy with the neutrino. When a sample contains many atoms of a beta emitting radionuclide, the result is a beta spectrum with a broad energy distribution between zero and Emax (a diagram of a representative beta spectrum is shown below). The average beta energy is about 1/3 of the maximum energy.



For most beta emitters, the decay energy is also shared by one or more gamma rays. However, there are a few instances where no gammas are emitted. These radionuclides are called pure beta emitters. Examples include H-3 (tritium), C-14, P-32, P-33, and S-35. Pure beta emitters are convenient for research applications where highly penetrating radiation is not required, since the external hazard is greatly reduced. Coincidentally, these elements are also components of important organic compounds. This has led to use of these radionuclides in a wide variety of labeling procedures. An example of beta decay is H-3:

MeVHeH 0186.032

31 +++→ − νβ

(beta) (neutrino) (kinetic energy of beta)

Average and maximum beta energies for selected nuclides are listed in Appendix 1,

Figure 2.

c. Electron Capture (EC)

When an atom contains too many protons in the nucleus for stability, one of these protons can combine with an inner-shell electron in the process of electron capture. The result of this reaction is the conversion of a proton and electron into a neutron.

ν+→+ − nep 1

011

(proton) (electron) (neutron) (neutrino) Electron capture, therefore, has the effect of reducing the atomic number of the parent by 1, with the parent and daughter having the same atomic mass number. The vacancy left by electron capture must be filled. An electron from a higher-energy shell “falls down” into the inner-shell, and a x-ray is emitted. This leaves another vacancy, which is filled by an electron from an outer shell. The process is repeated until all lower-energy shells are filled. A cascade of characteristic x-rays accompanies these transitions. Gamma rays may also be emitted by the daughter nucleus if the decay energy is not imparted totally to the neutrino.

An example of electron capture decay is Cr-51:

MeVVCr 752.05123

5124 ++→ ν

(parent) (daughter) (neutrino) (sum of decay energies)



A 0.32 MeV gamma is emitted in 9% of the Cr-51 decay processes. Weaker x-rays (up to 0.1 MeV in energy) are also emitted as electrons move to replace inner shell vacancies.

d. Positron ( )+β Emission

When the available decay energy is large and an atom has too many protons in the nucleus, it may decay through positron emission instead of electron capture. Positron emission is sometimes called beta (+) decay. The process is similar to beta (-) decay, except that the type of radiation emitted is an antimatter electron (positron). During positron emission, one of the protons in the nucleus is converted to a neutron, a positron, and a neutrino:

ν++→ +enp 1

011

(proton) (neutron) (positron) (neutrino) The neutron remains inside the daughter nucleus. The positron and neutrino escape. This yields a daughter nucleus with one proton less than the parent but with the same atomic mass number as the parent.

A positron has the same mass as an electron but is opposite in charge. As it travels, it slows down through interactions with other atoms in the vicinity. After is has slowed down, it combines with any nearby electron in an annihilation (matter-antimatter) reaction. In this annihilation reaction, the destruction of the electron and positron creates two gamma rays, or photons. The photons each have energies of 0.511 MeV and are emitted in opposing directions.

Positron emitters are rarely used because they are inconvenient to produce. Most positron emitters decay after only a brief storage time (short half-life). They are ordinarily produced using a particle accelerator (cyclotron). The most common use of positron emitters is for positron emission tomography. This technique takes advantage of the opposing directions of the two annihilation gammas. Positron emission tomography is used to diagnose some types of brain tumors and other brain disorders.

An example of positron emission is Na-22:

MeVMeVNeNa 82.102.100

2210

2211 ++++→ + νβ

(parent) (daughter) (positron) (neutrino) (annihilation gammas) (remainder of decay energy) The shape of the positron energy spectrum is similar to the beta spectrum.



e. Internal Conversion

In some instances, the decay energy normally released as a gamma ray is imparted to an inner-shell electron. The electron leaves the atom with a kinetic energy that is equal to the original gamma energy minus the binding energy of the electron. This is called internal conversion. Internal conversion competes with gamma emission. It is a significant effect for a few gamma-emitting radionuclides such as Cs-137 and In-113. Internal conversion electrons are monoenergetic, meaning that they are emitted with discrete energies instead of a broad spectrum of energies. Since a vacancy exists in an inner electron shell after internal conversion, x-rays are emitted as electrons move successively from outer shells to fill the lower-shell vacancies. This creates a series of characteristic x-rays. Occasionally, another form of internal conversion may result when energy normally released as a characteristic x-ray is imparted to an orbital electron. The electrons emitted in this process are called Auger electrons and tend to have very low energies. This makes them difficult to detect.

f. Internal Transition

When a parent nuclide decays and the decay particles do not carry away all of the energy, the daughter nucleus is left in an excited state (an excess of energy). Normally, the energy is released immediately as a gamma ray or internal conversion electron. However, for some daughter nuclides, the excited state persists for minutes or hours. This is called internal transition. The daughter nuclide is designated with the symbol “m” after the atomic mass number to indicate a meta-stable state. Eventually, the daughter nuclide releases the excitation energy through gamma emission. The daughter nuclide can be chemically separated from the parent. By itself, the daughter nuclide behaves like a pure gamma emitter. This can be useful for some forms of medical imaging where highly penetrating radiation is needed. When a radionuclide is injected for a nuclear medicine study (such as a bone scan), any short-range alpha or beta radiation present in the decay would be absorbed within the patient. This would cause unnecessary dose to the patient and would not help the imaging process. If a pure gamma emitter is available, the image quality is increased and the patient dose is decreased. This can be achieved through use of an electron capture radionuclide or internal transition radionuclide.

One radionuclide frequently used in imaging studies is technicium-99m, the internal transition daughter product of molybdenum-99:

MeVTcMo m 37.19999 ++→ −β



The decay of molybdenum-99 releases a beta particle (maximum energy 1.23 MeV), leaving an excess of 0.14 MeV in the excited state of the technicium-99m daughter. Technicium-99m can be chemically separated from the molybdenum parent for use in Nuclear Medicine procedures. Technicium-99m later releases the energy as a gamma ray (the half-life of Tc-99m is 6 hours).

( )MeVTcTcm 14.09999 γ+→

6. Decay Schemes and Energy Levels

Many radionuclides decay through several possible combinations of particle and gamma ray energies, corresponding to different energy levels of the daughter nucleus. It is convenient to depict these energy levels as decay schemes. Decay schemes for selected nuclides are included in Appendix 1, Figure 3. To help with the interpretation of these diagrams, some examples and explanations are included in the next few sections.

a. I-131 Decay Diagram (Beta Decay Example)

Iodine-131 is typical of a complex beta decay scheme. There are five different nuclear energy levels that correspond to different values of Emax (maximum beta energy). Each beta (-) emission for I-131 has one or more corresponding gamma emissions.

Table 4 – Energy Levels for I-131 Beta (-) Decay, (Q = 0.97 MeV)

Beta Energy (Emax)

Percentage of Decay Events

Associated Gamma Ray Energies (MeV)

0.25 MeV 1.6% 0.72

0.33 MeV 6.9% 0.64

0.47 MeV 0.5% 0.50 or (0.33 and 0.17)

0.61 MeV 90.4% 0.36 or (0.28 and 0.08)

0.81 MeV 0.6% 0.16 (from Xe-131m)

The first two columns in Table 4 show the beta endpoint (maximum energy) and the percentage of events in which this decay occurs. The third column shows the possible gamma emission(s) associated with each beta decay. Gamma rays are emitted either as a single photon, or as several photons (shown in parenthesis). By adding the first and third columns, it is easy to demonstrate that the total beta and gamma energies are always equal to the Q value (total decay energy for I-131).



The corresponding decay scheme for I-131 is shown below:

The parent nucleus, I-131, is shown at the top left corner. The half-life of I-131 is equal to 8.05 days, as shown in parenthesis. The energy levels of the Xe-131 daughter are shown as a series of horizontal lines. The daughter nucleus is located to the right of the parent nucleus because it has a higher atomic number (Z). Each line corresponding to the daughter nucleus is shown with the energy level, in MeV, at the right side of the diagram. The “ground state” (lowest energy state) of the daughter nucleus is indicated by an energy of 0.0 MeV (bottom line of diagram). Since the Xe-131 nucleus does not undergo radioactive decay, no half-life is shown. Beta emissions are indicated by arrows drawn from the parent nucleus (top left corner) to the different energy levels of the daughter. The beta energy, Emax, is obtained by subtracting the nuclear energy level from the decay energy, Q. For example, the energy of the first beta (β-1) is 0.970 – 0.7229, or 0.247 MeV.

Gamma rays are depicted as vertical lines traveling from higher energy levels to lower energy levels. They correspond to transitions where the daughter nucleus looses some or all of the remaining decay energy. During the first beta (β-1) decay the I-131 nucleus emits a 0.247 MeV beta to the 0.7229 MeV energy level of Xe-131. All of the remaining 0.7229 MeV is emitted as a single gamma ray. An example of multiple gamma emissions following beta decay is found in the (β-4) decay to the 0.3645 MeV energy level. Here, the remaining energy may be emitted as a single gamma ray of 0.3645 MeV, or as two gamma rays (0.2845 MeV and 0.0801 MeV). The gamma ray energies are equal to the difference in the nuclear energy levels. The numbering of the beta particles and gamma rays is usually arbitrary; this is done primarily so that additional notes can be included about relative abundance and the probability of internal conversion. The diagrams show

(11.8 d)

0.7229

0.0γ1

γ2

0.6370

0.16390.0801γ3

γ4γ5

γ6

γ7γ8

γ9

β −1 1.6%

β −2 6.9%

0.5030β −

3 0.5%

β −4 90.4% 0.3645

0.1772β −5 0.6%

Xe 54131m

XeStable 54131

53131I (8.05d)

Q = 0.970 MeVβ −



only nuclear energy levels and do not include characteristic x-rays emitted during transitions by electrons outside of the nucleus.

b. Zn-65 Decay Diagram (Electron Capture and Positron Emission)

Nuclides that decay through electron capture may also decay through positron emission if the Q value (available decay energy) is greater than 1.022 MeV. This amount of energy is necessary for the creation of two, 0.511 annihilation gammas. The decay scheme for Zn-65 is shown as an example of this type of decay. The half-life of Zn-65 is 245 days (as shown in parenthesis).

er nucleus are much simpler than in the preceding example for

o

1.115

3065 Zn (245 d)

QEC = 1.35 MeV*

Cu2965Stable

0.0

γ1

1β + 1.7%

EC1 49%

EC2 49%

* Maximum β + Energy = QEC - 1.022 MeV

The daughter, stable Cu-65, is shown below and to the left of the parent. This convention is followed because the atomic number (Z) of the daughter is less than the Z of the parent for electron capture. The energy levels of the Cu-65 daughtI-131 decay. There is only one level above ground state. Electron capture transitions are shown as straight arrows from the parent tthe daughter. Two electron capture transitions are possible. In the first, occurring 49% of the time, the daughter nucleus is left with an excitation energy of 1.115 MeV. This is released as a 1.115 MeV gamma ray. In the second electron capture transition (also occurring about 49% of the time), thedecay proceeds directly to the ground state of Cu-65. No gamma ray is emitted. In both of these transitions, characteristic x-rays are emitted as electrons fall into vacancies in electron shells. This occurs outside the

ucleus and is not depicted in the decay diagram. n During 1.7% of the decay events, the decay proceeds through positron emission instead of electron capture. Positron emission is depicted by a vertical line connected to a diagonal arrow. The vertical line symbolizes the



energy released as two annihilation gammas when the positron combines with an electron outside the atom. The diagonal arrow represents the

ositron. The energy of the positron is obtained by subtracting the daughter 11

MeV gamma energies.

penergy level from the Q value (decay energy), then subtracting the two 0.5

)511.0(2)( MeVnucleusdaughteroflevelenergyQE positron ×−−=

In this case, the energy level of the daughter is 0.0 (ground state), and the maximum energy of the positron is equal to (1.35 – 1.022) MeV, or

0.33 MeV.

. Ra-226 Decay Diagram (Alpha Decay Example)

Alpha decay is symbolized by double lines within the decay scheme. The decay energy, Q, tends to be very large. The daughter product is depicted to the left of the parent because the Z of the daughter is less than the Z of the parent. Radium-226 provides a straightforward example of alpha decay:

ll decays, an alpha particle

c

In 94.6% of all Ra-226 decays, an alpha particle with energy 4.894 MeV is emitted. Since this corresponds to the ground state of Rn-222, no orresponding gamma ray is released. In 5.4% of ac

with an energy equal to (4.894 – 0.1857) or 4.708 MeV is emitted. The remaining 0.1857 MeV is emitted as a single gamma ray.

α 1 5.4%α 2 94.6%

Rn (3.82 d)86222

Q = 4.894 MeVα

Ra (1602 y)88226

0.00.1857

γ



tion of Radiation with Matter

zing and Nonionizing Radiations

C. Interac 1. Ioni

he types of radiation described in the preceding sections are ionizing radiation. Ionizing radiation is distinguished from other types of energy by its ability to

roduce ionization in materials. Ionization is the removal of orbital electrons fromnon

clude ultraviolet and visible light, infrared light, radio waves, microwaves, and e otherwise noted, this

iscussion will apply only to ionizing radiation. 2. Con

Ioniz the type and energy of the radiation and material being traversed. Regardless of the mechanism of interaction, the consequences are ionization and excitation of atoms in the material.

a. Ionization

Ionization is the process of removing one or more orbital electrons from an atom. This produces ion pairs: one or more free electrons along with a positively charged atom (ion). Both the charged atom and the free electrons can react with other atoms in their vicinity to produce chemical changes in the material. During interactions of ionizing radiation with matter, a large amount of kinetic energy can be imparted to the free electrons. This energy is sometimes large enough so that the free electrons behave like beta particles to produce ionization. When the free electrons are capable of producing ionizations, they are called delta rays. These secondary electrons produce a track of damage along the path of the radiation. In a biological system, this damage takes the form of broken molecular bonds and free radicals (atoms that readily form chemical bonds).

b. Excitation

Excitation occurs when radiation deposits energy, but the energy is not

el of the

pens, excitation process.

T

p an atom. Radiations that cannot produce ionization are known as ionizing radiation. Some familiar examples of nonionizing radiation

inelectromagnetic fields from household wiring. Except wherd

sequences of Interactions (Ionization and Excitation)

ing radiation may interact through a variety of processes, depending upon

sufficient to produce ion pairs. Small amounts of kinetic energy are transferred to atoms in the material. This increases the energy levatom or molecule without actually breaking chemical bonds. The increase in energy takes the form of molecular vibration or rotation. When this hapthe result is a (small) rise in temperature triggered by the



Some of the energy deposited by ionizing radiation is lost through excitation emperature. However, the ared to the damage produced by

of ionizing radiation will die g before a detectable rise in temperature

al

3.

h orbital cle interacts with

nough energy to allow ionizations to occur from the newly-electrons. Some of the energy may also be released as x-rays he type and probability of these interactions is related to the

har a.

ticle Velocity Corresponding

processes and an accompanying increase in tincrease in temperature is insignificant compionizations. A cell exposed to very large doses from ionization-produced damage lonis produced.

Nonionizing radiation can only deposit energy through excitation reactions.For most forms of nonionizing radiation (such as radio waves and infrared light), the effect is limited to heat. Ultraviolet light can produce biologicdamage through photochemical reactions as well as heating.

Charged Particle Interactions

Charged particles deposit energy primarily through collisions witelectrons. The collisions occur when the electric field of the partithe electric field surrounding the orbital electron. If the particle has a negative charge, it “pushes” the electron out of its orbit. If the particle is positively charged, it exerts a pull on the electron that removes it from the original orbit.

Collisions may impart ereleased secondary bremsstrahlung). T(

c ge and velocity of the incident particle.

Beta Particles

Beta particles (electrons and positrons) travel at very high velocities, comparable to the speed of light. Several examples are provided in Table 5.

Table 5 – Beta Particle Velocities

Particle Maximum ParNuclide Type Energy (Emax) To Emax (% of speed of light)

H-3 β- 0.0186 26%

C-14 β- 0.156 64%

P-32 β- 1.710 97%

O-15 β+ 1.738 97%

Since the particle velocity is initially high, it has little chance to interact with an orbital electron unless it passes very close to that electron. Interactions are widely spaced (in terms of atomic dimensions) because the probability of interaction is so low. However, when the particle does interact with an



orbital electron, a significant fraction of the particle’s kinetic energy can be transferred to the electron during the collision. As the particle slows, it becomes more likely to interact with other orbital electrons. The net effect is for beta particles to lose their energy in a diffuse manner (compared to alphas) and follow paths that can be marked by sharp changes in direction. A representation of a low-energy beta particle track is shown below:

age depth represents the maximum distance of travel in the material and is called the particle range. The range

to the energy and charge of the particle. For electrons, the

As shown in the diagram, the net distance traveled by the beta particle is shorter than the path length. This aver

differs according range is approximated by the following equation:

{ } ( )MeVEforEcmRange E 5.2412.0 ln0954.0265.1⎞⎛ ⋅−)( <⋅⎟⎜≈

w the ic grav ial ae energy MeV at the expression E{ 954lnE} is the beta energy (in MeV) raised to the power indicated in the brackets. It is not t ential nctio nd water, ∆ = 1.0. A further discussion o rticle nge i ection D.3.

b. B rahlung

When a beta par icle in e electric field of the

e field surrounding an orbital electron), it looses energy by changing

r

⎟⎠

⎜⎝ ρ

here ∆ is specif ity of the mater nd E is the beta particle or lectron in . Please note th 1.265-0.0

he exponf beta pa

fura

n. For tissue as provided in s

remsst

t teracts with th nucleus (instead of thdirections and releasing an x-ray. The energy of the x-ray is equal to the energy lost by the beta particle. These x-rays are called bremsstrahlung, obraking radiation.



The probability of bremsstrahlung production is small for low-Z materials such as tissue or plastic. However, the amount of energy released as bremsstrahlung is proportional to the atomic number of the absorber. This principle is the basis for x-ray production. In an x-ray tube, a beam of high energy electrons is directed against a metal target (typically tungsten). The high Z of the metal target increases the yield of x-rays. For the same reason, it is usually desirable to shield high-energy beta emitters with plastic or other low-Z materials. This minimizes unwanted

c.

hen a positron (β+) reaches the end of its range, it combines with a nearby orbital electron in an annihilation reaction (as described previously). The electron (matter) and positron (antimatter) disappear, and two 0.511 MeV amma rays are released. The annihilation gammas are emitted in opposite irections from each other.

d.

igh probability for bital electrons. They leave a dense path of ion pairs and in a short range. In addition to the slow speed, heavy

ility to penetrate the outer layer of skin.

production of bremsstrahlung x-rays. If lead or some other high-Z shielding material is used, it is sometimes necessary to increase the thickness and weight of the shield to account for this x-ray production.

Annihilation

W

gd

Alpha Particles

Alpha particles are approximately 7300 times more massive than beta particles. Heavy charged particles such as alpha particles travel at velocities much slower than the speed of light and have a hinteractions with orxpend their energye

particles are barely deflected by each interaction; therefore their path is short and straight. The range of a 5 MeV alpha particle is approximately 3.5 cm in air, or 0.004 cm in tissue. Alpha particles are not considered to be an external hazard because of their inab



4. Electromagnetic Radiation Interactions

a.

Gamma and x-ra electromagnetic energy. energy

than gammand gamma

or nucleus. Instead, photons produce ionization indirectly through reactions

c

b.

a

ugh

shielding material for most x-ray energies.

Gamma and X-rays, General

ys are photons, or packets of Because of their mechanism of production, x-rays tend to be lower in

a rays. Other than that, there is no difference in the way x-rays rays interact with matter.

Photons travel at the speed of light and have no charge. They cannot create ion pairs by interacting directly with the electric fields of an orbital electron

that release energetic, charged particles (usually electrons). The reactions that are most prominent for radiation protection issues are the photoelectrieffect, Compton scattering, and pair production. The probability of each process varies with the photon energy and Z of the material. Photoelectric Effect In the photoelectric effect, the incident photon energy is transferredcompletely to an inner-shell (orbital) electron. The photon disappears, andphotoelectron is released. The energy of the photoelectron is equal to the incident photon energy minus the binding energy of the electron. Photoelectrons are released from x- and gamma ray interactions with enoenergy to produce ionization in the surrounding material.

The probability of a photoelectric interaction is proportional to Z4 and inversely proportional to E3. This means that the photoelectric effect is only prevalent for low energy photons and high-Z absorbers. For this reason, lead s an excellent i

Photoelectric absorption can occur for very low energy photons as well. However, the resulting photoelectrons are not ionizing. This effect is the basis for many electronic devices that detect light.



c. Compton Scattering

Compton scattering occurs when a photon interacts with an outer-shell

in the process. If the interaction parts enough energy to the secondary electron, it can produce ionizations

ing can be

ansferred to the electron in a single scattering event.

Compton interactions are the most probable type of interaction for x-rays and gamma rays in tissue. The probability of a Compton interaction decreases slightly with increasing Z of the material.

d. Pair Production

When a photon has energy in excess of 1.022 MeV, it can interact with the strong forces near the nucleus of an atom in a pair production reaction.

he photon disappears and is replaced by one electron and one positron,

mall amount of

tion. However when the

(orbital) electron that has a binding energy much lower than the photonenergy. Only part of the photon energy is transferred to the orbital electron. The overall result is that the photon changes direction and loses energy. Theorbital electron is released from the atomimin the material. The photon may be scattered in any direction between 0 and 180 degrees. The energy loss of the photon is related to the scattering angle. For high energy photons, the scattering angle is usually low and little energy is imparted in any one Compton event. For low energy photons, the scatterangle can be much larger, and nearly all of the photon energytr

Temitted in opposite directions. The value of 1.022 MeV is the energy equivalent (E = mc2) of the mass of an electron plus a positron. Any remaining kinetic energy (above 1.02 MeV) is shared equally by the electron and positron, minus a very senergy shared with the atomic nucleus. The electron and positron deposit energy as they travel through the surrounding medium, creating ionization and excita



(antimatter) positron slows down, it combines with an electron in an mass is converted back to two photons, each

having energies of 0.511 MeV.

on

. l

interactions.

s 0

D. Time, Distance and Shielding The physical principles described in the preceding sections can be put to use in a radiation protection setting. These are expressed as the basic mechanisms of time, distance, and shielding. 1. Time

This principle is fairly simple. If you enter a radiation area, the amount of occupational exposure will be proportional to the time spent in the area. Although this sounds trivial, it is easily forgotten in the work environment. It is important to work efficiently, without wasting time or making mistakes (which could incre Anot al decay (section B.3). If you have a source that is no longer needed, it can be allowed to decay in a well-

osal. This reduces the amount of radioactive material isposed of as waste, and reduces any radiation exposure involved in the handling

of th

2. Dist

For any point source of radiant energy (including ionizing radiation), the intensity of thawa e distaConv a source of penetrating radiation, it can lead to a great deal of unnecessary exposure.

annihilation reaction. The

The overall effect of pair production is the conversion of the incident photinto two, 0.511 MeV annihilation photons emitted in opposite directions. The only energy loss from the pair production interaction is the “left over” energy (above 1.022 MeV) which is imparted to the secondary electron and positronThe two, 0.511 MeV photons may subsequently deposit energy in the materiathrough Compton Pair production is more prevalent for high Z materials than for low Z materials. For lead, it becomes a significant interaction at photon energieabove 2 MeV, and the dominant interaction for photon energies above 1MeV. For low Z materials such as tissue, it is rarely significant (unless photon energies of tens of MeV are present).

ase your radiation exposure).

her facet of the “time” principle is exponenti

shielded area prior to dispd

e material.

ance (Inverse Square Law)

e radiation increases as you approach the source and decreases as you move y from the source. The difference in intensity can be dramatic. Increasing thnce from the source is an efficient method of reducing occupational dose. ersely, if you work unnecessarily close to



The ose rate is in

Inverse Square Law for a point source of radiation states that the dversely proportional to the distance from the source:

2

2

112 ⎟⎟

⎠

⎞⎜⎜⎝

⎛=

ddII

I is the radiation intensity and

Here d is the distance from the source. As an example, suradi a dista

,ppose that you measure a thousand counts per minute (cpm) on your

ation detector placed one foot from a radiation source. If you moved back to nce of two feet, the count rate would be:

( ) cpmfeet

ot 250212 =⎟⎟

⎠⎜⎝

⎟⎜

Note that the Inverse Square Law works to increase radiation exposure when the is decreased. It can also be called the Inverse-r2 Effect. The r2

represents radius squared, which is the same as distance squared, in the tion

ntact with a radiation source.

focpmdII 1100022

1 ⎞⎜⎛

⋅=⎟⎞

⎜⎛

=d2 ⎠⎝

Each time the distance from the source is doubled, the intensity is reduced by afactor of four.

distance

equations above. The following is an approximation of the increase in radiadose as you approach a small-diameter source.

Theoretically, the dose rate increases to infinity as the distance decreases to zero. In reality, this does not happen. At very small distances, the point source approximation no longer applies and the dose remains finite. However, the dose rates can become extremely large at the point of co



For this reason, you should be extremely cautious about handling sources of penetrating radiation. Normally, tongs or forceps must be used to provide some

istance between you and the source. If the radiation is easily attenuated articularly if it is a pure low-energy beta emitter), there may be enough

shielding around the material to permit holding the container in a gloved hand. Otherwise, the source must not be handled directly.

3. Shielding

ten

members of the public. s in medical x-ray facilities, nuclear medicine

facilities, radiation therapy facilities, and particle accelerators.

hielding takes advantage of the process of attenuation. Attenuation is the duction in intensity when a beam of radiation passes through a material. The

ritium. For more penetrating beta

energies, the skin still provides some protection. However, the degree of protection varies with the maximum beta energy and the thickness of the outer layer of skin.

d(p

If work must be performed in the vicinity of an intense radiation source, it is ofpossible to construct a shield. This blocks most of the radiation, allowing the worker to reduce his or her occupational dose. If a facility is placed next to an area where non-radiation workers are present, shielding is used to ensure that the

djacent areas are exposed to less than the dose limits foraThe most common use of shielding i

Sreamount of attenuation is a function of the composition of the material, as well asthe type and energy of the radiation.

a. Charged Particle Attenuation

Charged particles are easily shielded because of their limited range inmaterials (as discussed in section C.3.). Often, the thickness of the outer protective layer of skin is sufficient to stop the radiation. This is the case foralpha particles and low energy betas from t



For radiation protection purposes, the thickness of the outer, “dead layer(stratum corneum) of skin is considered to be 0.007 cm. This value underestimates the protection of the outer layer of skin for the hands. Keep in mind that the shielding of the source container is not included in theabove diagram. Almost any added thickness fro

”

m any container is sufficient

to stop beta particles from carbon-14 and sulfur-35 from reaching any ing cells within the skin. For this reason, carbon-14 and sulfur-35

are not ordinarily considered to be external hazards.

dose eta

ergy, even a lesser amount of shielding can produce a noticeable benefit.

ergy betas. In scattering, some of the beta particles change direction and can be reflected back from the shield or to the

s, multiple scattering can allow some of the

beta particles to bypass the shield, as shown in the diagram. Bremsstrahlung is the production of x-rays in materials by electrons or beta particles (as described in section C.3.). Although it is usually not a safety problem, bremsstrahlung can produce a measurable count rate around high-energy beta sources. When a high-Z material such as lead is used to shield an intense, high-energy beta source, additional lead should be added to reduce the intensity of the bremsstrahlung x-rays. The amount of scattered radiation may not be of concern from a safety standpoint. After all, the purpose of the shield is to reduce the dose rate from the source (not to eliminate it altogether). However, if shielding is required

proliferat

For beta energies greater than 0.2 MeV, the incident betas can produce a to the skin. Additional shielding is often beneficial (see section E.9.b. on BDose Rates). Although the standard approach is to provide shielding at least as thick as the range of the maximum beta energy, this is not necessary unless the dose rates near the source are high. Since most of the beta particles have energies that are 1/3 of the maximum beta en

Two physical processes that decrease the effectiveness of beta shielding are scattering and bremsstrahlung. These processes are more significant for high-energy betas than for low-en

side of the shield. In extreme case



to maintain doses within occupational limits, then it is always necessary toevaluate the shield’s effectiveness prior to actual use.

b. -ray and Gamma Ray Attenuation

photon passes through a ickness of material it has a certain probability of interaction. The

arrangement of the shield, and is not included in this calculation. As an example, estimate the reduction in intensity for 50 keV x-rays if a lead shield 1.0 mm in thickness is installed. Compare that value to the reduction for 1 MeV gamma rays shielded by the same thickness of lead ( : = 88.7 cm-1 for 50 keV x-rays; : = 0.796 cm-1 for 1 MeV gammas). The reduction in intensity can be calculated from the ratio I/I0.

For 50 keV x-rays (1 mm lead),

X

Unlike charged particles, x-rays and gamma rays do not have a fixed range. X-rays and gamma rays interact with materials through photoelectric absorption, Compton scattering, or pair-production (depending upon the photon energy and Z of the material). When a single thprobability of interaction per unit thickness of material is called the linear attenuation coefficient, :. The attenuation equation for x-rays and gamma rays is similar to the exponential equation for radioactive decay.

xeII µ−⋅= 0 In this equation, I0 is the intensity without the shield, I is the intensity with the shield in place, and x is the thickness of the shield. The attenuation equation is an approximation, since x-rays and gamma rays scatter easily. The contribution of scattered radiation depends upon the size and

00014.0)1.0()7.88(

0

1

=== ⋅−− − cmcmx eeII µ

The intensity after shielding is only 0.01% of the original intensity (an acomplete reduction). For 1 MeV gamma rays (1 mm lead),

lmost

92.0)1.0()796.0(

0

1

=== ⋅−− − cmcmx eeII µ



Here, the intensity after shielding is 92% of the original intensity (only an 8%reduction).

verted to 0.1 cm to keep the same

units for : and x. This example illustrates the dramatic difference in

igh

meter,

ired to reduce the radiation intensity by 50% /I = 0.5).

Note that the thickness, 1.0 mm, was con

shielding effectiveness for different energies in high Z materials. It also illustrates why lead shielding is more cost effective for x-rays than for henergy emitters. The attenuation coefficient is often related to a more convenient parathe half-value layer (HVL). The half-value layer is the approximate thickness of material requ(I 0

HVLandHVL 693.0693.0

== µµ

l

Occasionally, tabu ations will be provided for tenth-value layer (TVL). The tenth-value layer is the approximate thickness of material required to reducethe radiation intensity to 10% of the original value (I/I0 = 0.1).

TVLandTVL 30.230.2

== µµ

By taking advantage of these definitions, an alternative form of the attenuation equation becomes:

TVLHVL NN

IIorI

⎟⎞

⎜⎛=

1I

⎟⎠⎞

⎜⎝⎛=

⎠⎝ 101

2 00

here NHVL is the number of half-value layers, and NTVL is the number of nth value layers. This can be a quick and easy approach to shielding

s a final shielding example, suppose you need to place a very intense Cs-137 an existing office. It is necessary to

educe the exposure rate so that the administrative personnel in the next office receive less that 100 mrem in a year (based on a 40-hour week). If the measured dose rate on the other side of the wall is 5.0 mrem/hour, what thickness of concrete must be added? For this example, use a half-value layer of 2.5 inches for Cs-137 gammas in concrete.

wtecalculations. A graph of HVL vs. energy is shown in Appendix 1, Figure 5. Asource (0.67 MeV gamma rays) next tor



1) Find the ratio of I/I0:

(0.048 mrem/hr)/(5.0 mrem/hr) = 0.0096

I0 = 5.0 mrem/hr

I = 100 mrem/yr x (1 year/52 weeks) x (1 week/40 hours) = 0.048 mrem/hr

I/I0 =

2) Rewrite the equation to solve for the number of half-value layers required for I/I0 = 0.0096.

( )

( )21

0

0 lnln

21 IIN

II

HVL

NHVL

=⇒⎟⎠⎞

⎜⎝⎛=

( )( )

( )( ) layersvaluehalf

IIN 7.60096.0lnln 0 ===

3) Determine the concrete thickness that corresponds to this number of half-value layers.

x (thickness) = 6.7 half-value layers x 2.5 inches per HVL = 17 inches of concrete

7 inches of concrete would be required to provide the necessary shielding. If this shielding calculation were done for a real workplace, it would be necessary to adjust the calculation for the effects of scattered radiation. It would also be prudent to include an extra “margin of safety” in the shield thickness to anticipate voids (hollow areas) inside the concrete. The consideration of these details would eliminate the need for installing additional shielding after remodeling was completed (an expensive

y Of

e

HVL 5.0lnln 21

In this example, an additional 1

task). If a strong source of penetrating radiation is involved, shielding maalso be required for adjacent floors and exterior (as well as interior) walls.course, any design change of this magnitude would require approval from th

adiation Safety Office (and several other agencies) prior to the building Rmodifications. For most uses of radiation at the University of Washington, a precise shielding calculation is not required. When the shield is small and architectural factors are not a concern, the shielding can be deliberately overestimated. Often, it is sufficient to put up a sturdy wall of lead bricks



several times the required thickness. If a detailed shielding calculation is required, personnel from the Radiation Safety Office can provide assistance.

In any sh or otherwise), the user must always measure sh d’s Never as h

E. Basic ose Q itie

1. Historica

During the first few years after the discovery of x-rays, radiologists and scientists struggled with a lack of available means for quantifying the amount of radiation present. Since the hazards associated with high doses of radiation were not recognized prior to the 1920’s, the first unit of dose was biological – the skin erythema dose. This was the amount of radiation required to turn a person’s skin red. Unfortunately, this required the assistance of individuals who received considerably more radiation than modern occupational laws would allow. Thistragic method of detection was discontinued when the long-term hazards of such exposures were recognized and other standard techniques for radiation detection became available.

Quantitie econcept was expanded to include energy deposition in any material (dose) and ultimately, th t

2. International System (SI) Versus Traditional Units

Radi , rad aSysttradthe t For

3. Exp

Expochargamhistorically been the roentgen, R, named after the discoverer of x-rays. For conv (1/10

ield design (highly precise the iel effectiveness under worst-case working conditions.

less it is tested. sume that t e shielding is correct un

D uant s and Units

l Overview

s w re later developed to describe ionization in air (exposure). The

e risk of harm o an individual (dose equivalent).

ation quantities were traditionally expressed in units such as the roentgennd rem. In 1960, the International System of Units (abbreviated as SI, for

ème International) was adopted as the scientific basis of units. Just as the itional unit of length (the foot), now has a SI counterpart (the meter), all of raditional radiation quantities now have SI units. This can lead to confusion.

clarity, both sets of units are presented here.

osure

sure is the traditional quantity for radiation measurement. Exposure is the ge (either positive or negative) produced per unit mass of air by x-rays or ma rays as they traverse a collecting volume. The unit of exposure has

enience, exposure is sometimes expressed in units of milliroentgen, mR00th of 1 R).

mRR 10001 =



original definition of the roentgen was the amount of x-ray or low energy The

gamma radiation producing an ionization of one electrostatic unit (esu) of charge in on

The nd the conversion between the international system and the traditional system is:

(or

4.

osure, but is a more meaningful quantity. Absorbed dose is

ity

The traditional unit of absorbed dose was originally called the radiation absorbed d. The rad is defined as

an energy deposition of 100 ergs per gram of absorbing material.

een replaced in the SI system by the gray, Gy, which is defined as

e cubic centimeter of dry air at standard temperature and pressure.

SI unit for exposure is coulombs of charge per kilogram of air a

4−= kgCxR /1058.21

Exposure units are defined only for x-rays and low energy gamma rays when measured in air. Exposure should not be used when describing radiation dose in materials other than air, and it should not be used for beta or alpha radiationother charged particles).

Absorbed Dose

A more realistic assessment of the potential for radiation damage is provided by the absorbed dose, or energy absorbed per unit mass of material. This is harderto measure than expusually measured indirectly, either through measurements of exposure in air or by calibrating the output of a chemical or electronic detector to a known quantof radiation.

dose. Now the unit is known entirely by the acronym: ra

gergrad /1001 =

Smaller amounts of radiation are expressed in millirad (mrad), or 1/1000th of a rad. One rad equals 1000 mrad. The rad has bone joule of energy departed per kilogram of absorbing material.

radGyandkgJGy 1001/11 == In many low-Z materials, the absorbed dose is fairly close to the measured xposure in air. An amount of radiation producing an exposure of one R in air will

produce an absorbed dose of 0.87 rad in air or approximately 0.92 rad in a small volume of tissue.

e



The absorbed dose in a material varies with the energy and type of radiation as y to

and 1 cm for “total body” or deep dose. A measurement device, such as an “optically

”

5. Quality Factor (Q)

Some types of radiation (heavy particles, alphas and neutrons) have a heightened s of

particular type of radiation.

rticles are approximately 20 times more efficient (per unit y

her hand, if an lpha emitter is taken internally, it comes in close contact with various tissues in

the body. Then, the high quality factor for alpha emitters is important. For this reason, greater care is taken in handling alpha emitters to prevent ingestion or inhalation of these materials.

6.

ion to produce iological damage (the quality factor, Q). The relationship between dose

equivalent and absorbed dose is as follows:

well as the depth of penetration in the material. For this reason, it is necessardefine a set of standard measurement depths. For radiation protection purposes, standard reference depths are 0.007 cm for skin, 0.3 cm for lens of the eye

stimulated luminescent” (OSL) dosimeter or “thermoluminescent dosimeter(TLD), can be used to detect the dose at these reference depths.

ability to produce biological damage. These particles tend to leave dense trailionization rather than diffuse ionization. The concept of quality factor was developed to account for the differing degrees of hazard for various radiations. The quality factor, Q, is defined as the relative effectiveness for producing biological damage from a Alphas and heavy padose) in producing biological damage than betas or gammas. So, alphas and heavparticles are assigned a quality factor of 20. Neutrons are approximately 10 times more efficient than betas or gammas in producing biological damage (although this varies with energy). Neutrons are assigned a quality factor of 10 (unless specific corrections are made for energy). Betas and gammas are assigned a quality factor of 1. It must be emphasized that the potential for biological damage varies with both the quality factor and the absorbed dose. For example, alpha particles outside the body have a quality factor of 20 but produce zero dose in tissue (because they cannot penetrate the outer, protective layer of the skin). On the ota

Dose Equivalent The dose equivalent includes both the energy absorbed from a specific type of radiation (i.e., the dose in rad or Gy) and the ability of that radiatb

)(QfactorQualityxDoseAbsorbedEquivalentDose = The traditional unit of dose equivalent is the rem, originally called “roentgen equivalent man.” Small dose equivalents are expressed in mrem (1 rem equals 1000 mrem).



QxradDoseAbsorbedremEquivalentDose )()( =

QxmradDoseAbsorbedmremEquivalentDose )()(

=

The SI unit for dose equivalent is the Sievert, Sv.

QxGyDoseAbsorbedSvEquivalentDose )()( =

Since 100 rad = 1 Gy, it is also true that 100 rem = 1 Sv. As a sample calculation, compare the dose equivalent from a 0.1 rad dose of abeta and gamma radiations:

lpha,

Table 6 – Sample Dose Equivalent Calculations

Dose Quality Factor Dose Equivalent

100 mrad of Alpha (0.1 rads)

Qalpha of 20 2000 mrem (2 rem).

100 mrad of Beta (0.1 rad)

Qbeta of 1 100 mrem (0.1 rem)

100 mrad of Gamma (0.1 rad).

Qgamma of 1 100 mrem (0.1 rem)

7.

. ts are calibrated in terms of dose rate, exposure

e most common radiation units of rate are:

cpm (counts per minute) = counts per unit time

d dose (mrad), for example, would be the dose rate (mrad/hr) times the e,

Rate Units It is often useful to know the rate at which the exposure to radiation is occurringMost measurement instrumenrate or count rate. Th

mR/hr = exposure per unit time

mrad/hr = dose per unit time

mrem/hr = dose equivalent per unit time

The accruetotal duration of the exposure. Keep in mind that the shorter the exposure timthe lower the total dose:



Table 7 – Radiation Rate Examples

Rate Time Spent in Area Total Amount Received

100 mR/hr 6 minutes (0.1 hr) 10 mR

2 mrad/hr 2 working days (8 hr/day) 32 mrad

2 mrad/hr Continual occupancy (40 hrs/week and 52 weeks/yr)

4160 mrad

e workplace. The may be much lower than what you expect

osure rate of 30 mR/hr at a distance 3 inches from

spend 6 minutes ding 3 feet otal exposure would be (30 mR/hr x 0.1 hr) + (0.2 mR/hr

x 1 hour), or 3.2 mR. The un ute, cpm ated to ctive material present. This riate for searching contam acility. M ors that ts per minute are extremely sensitive to radiation. Users of these survey instruments are so believ gh dose se they have a measurable count rate. This is usually not true. If it is necessary to determine an external dose rate, it better to use an ionization chamber (measuring absorbed dose in air) than to try to convert from counts per minute to

quire information about dose rates and do not have an instrument urements, you may contact the Radiation Safety Office to

8. P

I ca rem y iation levels around a source before the source is purchased or used. This requirements and the need for personnel monitors (radiation badges), as well as for p h

. ma Ray Constant (Γ)

ay constant is defined as the exposure rate per curie of activity at a fixed distance. The units may include distance-squared instead of distance. At first glance, this may appear to be a misprint but it is actually

Also keep in mind that a person often moves around in thaverage amount of radiation received based on measurements close to the source. For example, suppose that you have a source that produces an expthe source and a rate of 0.2 mR/hr at a distance of 3 feet from the source. If you

holding the source (using forceps) and 1 hour stanfrom the source, your t

its of counts per min , can be rel the amount of radioa usage is approp

ination in a lab or fout trace amounts of

are calibrated in counost detect

metimes deceived into ing that a hi rate is present becau

dose. If you redesigned for dose measarrange for this type of radiation measurement. redicting Radiation Levels

t n be ext el useful to anticipate radcan be the basis for evaluating shielding

lanning ot er safety precautions.

a Estimation of Gamma Exposure: Specific Gam

The external radiation exposure rate (R/hr) from a gamma emitter can be predicted from the specific gamma ray constant, Γ, for that radionuclide. The specific gamma r



a more precise way of specifying the conversion factor. The equation for exposure rate is:

2dA

X =⋅Γ

H e exp gamma r , A is the so y, a source. e distance term is squared in the denominator. This reflects inverse-r2, the decrease in intensity with the square of the distance from the source.

y

r

se that a desk is to be placed 6 feet from a 10 microcurie source of iodine-131. Assume that the source container has enough material

ere, X is thurce activit

osure rate, Γ is the specificnd d is the distance from the

ay constant Note that th

The specific gamma ray factor, Γ, has been calculated for most commonlused radionuclides. Many of these are provided in Appendix 1, Figure 7. Foradionuclides not shown in Figure 7, the specific gamma ray constant can be determined based on the energy and the number of gammas emitted per disintegration. A graph of specific gamma ray constant versus energy is provided in Appendix 1, Figures 8 and 9. As example, suppo

to absorb most of the beta particles (only gamma rays are emitted). Predict the exposure rate at the desk.

From Appendix 1, Figure 7, Γ = 2.2 R cm2 per hr per mCi. To apply this factor, convert the source activity and distance into the same units used forthe specific gamma ray constant.

mCiormCiCi /1000 µ

Ci010.0

10 µ=

mCiAhere )(,

CimCi

CiAmCiA1000

1)()(

µµ ⋅=

cmcmft

ftcmDhere 183

/0328.06

)(, ==

ft0328.0cm

ftDcmD1

)()( ⋅=



Using consistent units:

hrRxcm

mCimCihrcmRd

AX /106.6

)183(010.0)//(2.2 7

2

2

2−=

⋅⋅=

⋅Γ=

Note that the source strength would decrease with time as radioactive decay

ion exposure. Additional shielding is clearly unnecessary for this purpose.

ng no beta dose)?

occurs; I-131 has a half-life of 8 days. Even if new source material were added frequently to replace the material “lost” to radioactive decay, the worker at the desk would only receive 0.011 R in a year. Since the limit for a radiation worker is 5 rem per year to the “whole body” (roughly the same as 5 R), this would be only 0.2% of the annual limit for radiat

Now, suppose that the worker is handling the 10 µCi I-131 source, which is contained in a thick vial of plastic, 3 mm (0.3 cm) in thickness. This amount of plastic would absorb the incident beta particles but would not stop the gamma emissions. At contact with the vial, what would be the maximumexposure rate to the person’s hand (assumi

hrRcm

mCimCihrcmRd

AX /24.0

)3.0(010.0)//(2.2

2

2

2 =⋅⋅

=⋅Γ

=

The limit for occupational exposure to the extremities and skin is 50 rem per

hielding was thin enough to allow beta articles to reach the hand. However, it is far preferable to use forceps or ngs when holding a source (unless that radiation cannot penetrate the

source container).

Note that this example would not apply if the source material were spilled were very thin (minimal reduction in

beta particle intensity). Calculations of skin dose from beta particles are included in the next section.

b. stimating Beta Dose Rates

Beta particles deposit all of their energy in a short distance (compared to gamma rays and x-rays). This has several ramifications. First, beta particles

very low energy betas (tritium), the heir energy in the outer, “dead” layer of skin. None of

these low energy betas reach layers of living cells and there is no shallow dose (dose at 0.007 cm). For nuclides with maximum beta energies of 0.15 to 0.2 MeV (C-14 and S-35), some of the higher energy betas in the source spectrum can produce a skin dose. However, these betas are attenuated substantially by ordinary laboratory gloves (and completely blocked by many

year (about the same as 50 R per year). In this instance, it is unlikely thatthe worker would receive a significant fraction of this limit unless the sourcewas a much higher activity or the spto

directly on bare skin, or if the container

E

are relatively easy to shield. For particles deposit all of t



standard laboratory containers). At energies greater than 0.2 MeV there is a ose to the skin but no potential for a significant deep dose (since beta

energies less than 2 MeV are completely attenuated by less than 1 cm of tissue).

s

er m the gamma

se rom the source

(minimal shielding). The beta dose rates include shielding from air, the outer layer of the skin, and a glove and/or thin plastic test tube. In an actual source, the beta particles are shielded significantly within the liquid carrier r solid matrix holding the radioactive atoms. Therefore, actual dose rates

d

Unfortunately, those beta particles that are capable of reaching the 0.007 cm depth in skin are very efficient in depositing their energy (thus, producing a dose). This is because the beta energy is deposited over a few millimeterdepth of tissue. Compare this situation to x-rays and gamma rays, which deposit their energy in a much more diffuse manner (over many centimeters of tissue depth). Since dose is energy deposited per unit mass of material, it is easy to see that the less concentrated energy deposition produces a lowdose. For unshielded beta-gamma emitters, the skin dose frocomponent is less than a few percent of the skin dose from the beta component. To illustrate the relative contribution of beta and gamma emissions, some doses are shown below for selected beta and gamma emitters. The skin dowas calculated for a 1 mCi point source at a distance of 10 cm f

oare often much lower than the ones shown in the Table 8.

Table 8 – Calculated Dose Rates (mrad/hr) at a 10 cm Distance from 1 mCi Sources

Beta Dose (with Various Shielding)

Max. Beta

Energy

UnSource (MeV)

shielded Source *

Glove (5 mil)*

1 mm Plastic Container*

se (Shielded by Up to a

Few mm Plastic)

Standard Glove, Plus

Gamma Skin Do

I-125 None None None None 7

H-3 0.0186 0 0 0 None

C-14 0.156 3 0 None 200

S-35 0.167 360 9 0 None

P-33 0.248 2300 500 0 None

I-131 0.606 5300 3900 190 22

P-32 1.71 3300 3300 2800 None

Y-90 2.27 2600 2600 2600 None * This

sour overestimates the dose rates because shielding within the source container and ce matrix is ignored.



,

s of radioactive materials. Since the dose rate is proportional to the ource activity, divide these values by 1000 to obtain the dose per microcurie

:

It should be emphasized that these calculations assume a 1 mCi sourcewhich is a fairly large activity. Most experimenters use much lower quantitiesat 10 cm from the source. You can adjust the results for inverse-r2 to estimate the dose at other distances. However, the use of inverse-r2 will overestimate the beta dose rate at distances greater than 10 cm (since air attenuation can provide a significant reduction in beta dose rate). As an example, determine the worst-case skin dose to a person holding a 10 microcurie (0.010 mCi) P-32 source in a test tube. Assume that the test tube diameter is 1 cm (radius of 0.5 cm), and ignore attenuation in the liquid

hrmradcmcm

cmatmCiperhrmradmCihrmradrateDose

/200,115.0

10)10/2800()010.0()/(

≈

⎟⎟⎠

⎞⎜⎜⎝

⎛⋅⋅≈

As stated earlier, this is a great overestimate, since it neglects a large amount of shielding provided by the liquid in the test tube. The inverse-R squared calculation will also tend to overestimate the dose near a source. However, this calculation underscores the advantage in us

2

ing forceps or tongs hold radioactive materials (where practical) if a high-energy beta emitter is

in use. An equally effe me kind of plastic “grip pad” or holde ith the container.

f bet are al wed to nta s

am of urf equuc r thi the p mea tionrat vironm s the u oves, la , and good

tam contro easures (s eys and cleanliness). Appendix 1, ure s the s n doses pro ced by an e distributiicro er cm2 the surfa of the skin. he protecti ided by

il Additional rm ncern ntamina on skin and clothing is provided in en igure aximum particle ranges in selected materials

sho ppen Figure

workin dioactive materials ng w ny add l preca mandat he chemiards nt in vironm Althoug rare, dire tam n can o hrough g of a glove or transfer of material

es in contact with skin, it should be washed off as soon

toctive approach might be to use so

r to shield the fingers from direct contact w

Icontprod

a emittersinationed. Fo

lo laboratory ss reason,

come in coaces or rimary

ct with bareipment), highns of protec

kin (from skin doses may be

in most labo ory en ents i se of gl b coats conFig

ination 10 show

l mki

urvdu ven on of

1 mordinary laboratory glo

curie p overves is also

celustrated in the graph.

T on prov

info ation co ing co tionAppare

dix 1, Fwn in A

11. Mdix 1,

beta12.

A lab coat and gloves are required when g with ra(alo ith a itiona utions ed by t cal or physical hazcon

preseinatio

the enccur t

ent). tearin

h it is ct skin

from a contaminated surface. If a microcurie quantity of a beta (or beta gamma) emitter com



as possible. The skin dose will not exceed the allowable limits unless the

o oat. This

ill prevent splashes to the skin of the wrist area. Monitor for contamination e

emoving contaminated protective clothing. A dose evaluation can be erformed to estimate the skin dose from the surface contamination.

In summary, beta emitters are much more easily shielded than gamma emitters. Beta particles are not capable of penetrating tissue to reach any internal organs (other than the skin). This makes them safer to work with

an gamma emitters in many respects. However, beta emitters greater than he

an eek (of beta emitters greater than 0.2 MeV in energy). However,

the examples in this section have shown that caution is necessary when e rates in

F. Intern

The radia absorptiodetermindosimetrprocess. verview of internal dosimetry will be given.

1. Upta

Radiabsoand

material is allowed to remain for several hours. Please contact RadiationSafety if you have any questions about potential skin doses. Fortunately, very few laboratories work with large quantities of radioactive materials. While working with millicurie quantities in unsealed form, you should always wear eyewear and two layers of gloves in addition to the precautions outlined in the preceding paragraph. You should also be sure ttape the wrist portion of the inner glove over the sleeve of the lab cwfrequently, and change the outer glove if source material is splashed on thglove. If accidental skin exposure occurs while working with millicurie quantities of material, call Radiation Safety after washing the area and rp

th0.2 MeV in energy are very efficient in producing a superficial dose to tskin. Particular care should be taken to avoid contamination of bare skin, since this greatly increases the dose rate. The results of many years of personnel monitoring (ring badge) have demonstrated that an individual is extremely unlikely to receive any measurable skin dose unless they work with activities totaling more th10mCi per w

working with radioactive materials. If you have questions about dosyour lab, the best approach is to call Radiation Safety for an on-site measurement.

al Radiation Dose tion dose from radionuclides deposited internally due to inhalation, ingestion,n through the skin, or from tissue puncture is often quite difficult to e. Since internal dosimetry involves both the physical factors of radiation y and physiological parameters, many uncertainties enter the calculation

or this presentation, only a general oF

ke

oactive material is taken into a person through inhalation, ingestion, rption, or injection. The efficiencies of uptake are dependent on the physical chemical forms of the material and the physiology of the individual. Uptake



or tr a. Thes dard man," but it must be recognized that in the real situation this will vary from individual to indivperscomp

2. Inte Matgene sfer of in n of radiconc r the standard person are available, but actual individual variations may be subs

3. Res The phys m relat e combination of biological elimination and physical decay is referred to as the effective decay constant and can

4. Ene The menthe c y of the radionuclide decay mode. For particulate radiation (alpha and beta), the radiations created from decay within an organ will be absorbed close to the site of

all of the particulate radiation energy created in t organ.

of

ometric computer models provide these parameters.

G. nnual Limits on Intake (ALI) The inta

ansfer coefficients are estimated from animal studies and some human dat

e coefficients have been determined for the hypothetical "stan

idual. Variation in breathing rates, for example, are very dependent on a on's physical condition and activity level. Eating habits may also provide eting elements for uptake. rorgan Transfer

erials that are taken into the body will move from one organ to another with rally predictable transfer coefficients. This may be as simple as the transoluble material through the G.I. tract or as complicated as the depositioum or calcium in bones. An important interorgan transfer is the entration of radioiodine in the thyroid. As noted above, parameters fo

tantial. idence Time

time that a radioactive material is in the body is dependent on both the ical decay constant of the radionuclide and the biological removal mechanised to the chemical and physical forms. Th

be easily converted to an "effective" half-life. rgy Deposition

amount of energy deposited in an organ is related to the parameters tioned above, but includes other factors, as well. One factor of importance is oncentration of material in the organ. Others are the type and energ

emission. Therefore, essentiallyn organ will be absorbed in thaa

However, for most organs and for most radionuclides, not all of the electromagnetic radiation energy (x- and gamma rays) will be absorbed in the organ. The absorbed fraction is related to the size of the organ and the energy the radiation. The absorbed fractions have been calculated for standard size organs. Fractions are also calculated for energy absorbed in nearby organs.

eG

A several parameters discussed above are combined to calculate the annual limits onke that will result in the allowable annual dose for critical organs. These limits



are e many radionuclides in common use.

H. An Regu radiation from manmade sources which are of no direct benefit to the individual. Due

ations, these dose limits include both internal and iscussion of the mechanism for combining internal and

extecalle

1.

ual limit for “whole body” dose is 0.05 Sv (5 rem) based on the sum of dose at 1 centimeter depth plus the effective dose

any internally deposited radionuclide. For most workers, cases,

the lens of the eye is 0.15 Sv (15 rem).

is 0.5 Sv (50 rem) based on the sum of rgan from

2.

pationally Exposed Person

he dose to an embryo/fetus during the entire pregnancy, due to occupational

xpressed in units of Bq or µCi. A list of ALIs is given in Appendix 1, Figure 13 for

nual Dose Limits

latory agencies have set allowable annual dose limits for individuals receiving

to recent changes in the regulexter al radiation doses. A dn

rnal doses is beyond the scope of this presentation, but the combined dosimetry is d total effective dose equivalent. Occupational Dose Limits for Adult Workers

a. Total Effective Dose Equivalent (“Whole Body”): he annT

the external deepequivalent from there is no significant ingestion or inhalation of radionuclides. In these the total effective dose equivalent is equal to the deep dose recorded by the dosimeter.

b. Lens of the Eye The annual limit to c. Skin and Extremity Dose The annual external dose limit at 0.007 cm depth is 0.5 Sv (50 rem) to the

skin or to any extremity. d. Other Organs

The annual limit for all other organsthe external dose at one centimeter depth and the dose to that ointernally deposited radionuclides (as determined by a bioassay).

Occupational Dose Limits for Minors

The occupational dose limit for minors is 10% of the above limits.

3. Dose to an Embryo/Fetus of an Occu

Texposure of a pregnant female that has declared her pregnancy to her employer, must not exceed 5 mSv (0.5 rem).



4

The total effective dose equivalent to individual members of the public must not a year. The dose to any unrestricted area from external not exceed 0.02 mSv (0.002 rem) in any one hour.

I.

regulations which require control of these doses, it is important to know about them to allow a proper perspective of what we can

1. s

atmo s. These partlight Cosmic radiation varies with the earth's latitude because of the effect of the

gnetic field. Doses are lowest at the equator and increase toward the is a very effective shield, so cosmic doses increase with

creasing altitude. Persons who live in the mountains or fly in airplanes receive ases following

olar flare activity.

he sea level whole body dose equivalent is about 30 millirem per year and

12 k dose equivalent of 2.5 mrem. A polar route flight to urope would result in nearly 10 mrem.

osmic radiation also produces radioactivity which becomes part of our food and air. radiequi r insignificant.

. Terrestrial Radiation

There are many primordial radionuclides in the earth's crust. The most well ily of

ne decays to the next. A total of 39 different radionuclides

. Dose Limits for Individual Members of the Public

exceed 1 mSv (0.1 rem) in sources of radiation must

Natural Background and Average Population Doses The dose we all receive continuously from natural background, occasionally from medical practices, and from some common commercial devices are part of our total radiation exposure. Although there are no

and should control.

Co mic Radiation

Cosmic radiation comes from deep space and from the sun. Before entering our sphere it consists mainly of high energy protons and heavier particle

icles interact in the upper atmosphere and cause "spallation" showers of er particles and protons which reach the earth.

earth's mapoles. The atmosphereina significant increase in cosmic radiation. Cosmic radiation incres Tincreases to about 40 mrem/yr at 1 kilometer. A jet flight across the country at

m altitude will result in a E C

Tritium, carbon-14, beryllium-7, and sodium-22 are the principle cosmogeniconuclides, but more than twenty others have been identified. The dose valent from C-14 is about 1 mrem/year, with the others being rathe

2

known are uranium and thorium. These are actually part of a whole famradionuclides, where oare included in these families.



Uranium and thorium and their daughter products are found in nearly all trations. One of the most important

atural radiation dose from two processes: a) the external radiation emitted from estion. tain

the s in

year in coastal cities but is as high as 140 mrem/year in some e additional dose equivalent to the epithelial cells of the don daughter inhalation is around 2400 millirem per year.

3.

spread and is incorporated und

4.

per year. This includes cosmic radiation, terrestrial

Colorado and eastern Washington

5.

ations such as x-ray or nuclear medicine procedures are restricted population which varies from year to year. Also, the tions of the body, and an x-ray beam is attenuated as it

y a

m medical procedures, but a generally accepted number is 50 millirem per year.

materials, although in different concendaughters is radon, an inert gas which is released to the atmosphere. Radon in soils tends to be drawn into the structures of most buildings. This radon can subsequently pose an exposure problem in the building. Humans receive a ndecay outside of the body, and b) the internal dose from inhalation and ingBecause of this, natural background radiation is higher when living in cerstructures that are conducive to buildup of radon gas, and in certain areas of country that have porous soil or high concentrations of primordial radionuclidethe surrounding materials. Terrestrial activity contributes an external whole body dose equivalent of around 30 millirem perColorado locations. Thlungs resulting from ra Internally Deposited Radionuclides

Another important primordial radionuclide is potassium-40. All potassium ontains about 0.012% K-40. Because it is so widely c

into the muscle mass, K-40 contributes a major part of man's natural backgroradiation, about 40 millirem per year. Natural Background Radiation Dose Equivalent

The average annual natural background radiation exposure in the United States about 300 millirem is

radiation, and naturally occurring radionuclides. The actual effective dose equivalent varies widely from location to location, primarily from fluctuations inradon concentration and building materials. Elevated natural background radiation levels are present in areas where there are naturally high uranium oncentrations in the soil (e.g., some areas of c

State).

Medical Radiations

A major component of man's radiation dose comes from medical applications. edical applicM

to a certain segment of theexposure involves only porpasses through the body. Current medical practice also involves the use of radiation in very high doses to destroy cancer cells. However, this occurs to onlsmall population and the tissues exposed usually represent a small portion of the body. For these reasons, it is difficult to assign an average effective dose equivalent to the population fro



Miscellaneous Dose

Many common materials and equipment emit radiation. These include smokedetectors, luminescent watch dials, mantles for gas lanterns, aircraft exit sigsome tableware, and anti-static devices. This generally accounts for an average population effective dose equivalent of about 10 millirem per year. Appendix 1, Figure 14 lists the radioactivity in many of these devices. Other activities such as the occupational use of radiation, the nuclear fuel cycle, and radioactive fallout accou

6.

ns,

nt for 1 to 2 millirem per year to the average opulation.

7.

oth manmade exposures and natural background radiation is about 360 millirem

p Total Average Population Doses

The total average effective dose equivalent to the U.S. population resulting for bper year.



Abbreviations and Symbols

A activity of a group of atoms

A mass number (nucleons)

ALI annual limits on intake

amu atomic mass unit

Bq becquerel = 2.7 x 10-11 Ci or 1 disintegration per second

c velocity of light

Ci curie

E energy

EC electron capture

esu electrostatic unit

eV electron volt

GBq Gigabecquerel

GeLi germanium lithium crystal

Gy gray = 100 rad (rad – unit of radiation absorbed dose)

h Planck’s constant

HVL half-value layer

I.C. internal conversion

keV kiloelectron volt

kCi kilocurie

LET linear energy transfer = keV per micron

MBq Megabecquerel

MeV million electron volt

µCi microcurie (10-6 curie)

mCi millicurie (10-3 curie)



nCi nanocurie (10-9 curie)

pCi picocurie (10-12 curie)

P.E. photoelectric effect

N neutron number (number of neutrons)

Q quality factor

Q value total decay energy

R roentgen

rad radiation absorbed dose

rem traditional unit of dose equivalent = absorbed dose (rad) times a quality factor (Q) SI international system of units

Sv sievert = 100 rem (rem - unit of dose equivalent)

t½ half-life

TLD thermoluminescent dosimeter

TVL tenth-value layer

v velocity

Z atomic number (number of protons)

Γ specific gamma ray constant

λ wavelength



Glossary

absorbed dose: The amount of energy absorbed per unit mass of material at the place of

interest. The unit of absorbed dose is the rad. One rad equals 100 ergs per gram.

activity: The rate of decay; the number of atoms that decay per unit of time.

alpha particle: A charged particle consisting of two protons and two neutrons (same as a helium nucleus).

annihilation radiation: Radiation produced when a particle unites with its antimatter equivalent, such as an electron and a positron. The particles disappear and two gamma rays are emitted (in opposing directions).

atom: The smallest subdivision of matter which retains the chemical properties of an element.

atomic mass: The mass of an uncharged atom of a nuclide, usually expressed in terms of “atomic mass units.” The “atomic mass unit” is one-twelfth the mass of one neutral atom of carbon-12; equivalent to 1.66 x 10-24 gram.

atomic mass number (A): The total number of protons and neutrons in the nucleus of an atom.

atomic number: The number of protons in an atom. Represented by the symbol Z.

attenuation: The reduction in intensity when a beam of radiation passes through a material.

becquerel: The international system of unit for activity, equal to one disintegration per second.

beta particle: An energetic electron which has been emitted from the nucleus of an atom, during radioactive decay.

bremsstrahlung: Secondary photon radiation produced in the form of x-rays by deceleration of charged particles passing through matter.

Compton scattering: Scattering of a photon by a loosely bound electron. Part (or all) of the energy and momentum of the incident photon is transferred to the electron and the remaining part is carried away by the scattered photon.

contamination (radioactive): Deposition of radioactive material in any place where it is not desired.



coulomb: A quantity of charge equaling one ampere per second. One coulomb is equivalent to the charge of 1.60 x 1019 electrons.

cosmic rays: High-energy particulate and electromagnetic radiations which originate outside the earth’s atmosphere.

counter - Geiger-Mueller: Highly sensitive, gas-filled radiation-measuring device. Operating at voltages sufficient to produce avalanche ionizations. Each count corresponds to one particle interacting in the detector.

counter - proportional: Gas-filled radiation detection device. The pulse produced is proportional to the number of ions formed in the gas by the primary ionizing particle.

counter - scintillation: An extremely sensitive measuring device which operates through the detection of light emissions produced in phosphors.

curie (Ci): The traditional unit of activity. One curie equals 3.700 x 1010 disintegrations per second. Several fractions of the curie are in common usage.

millicurie – mCi = 3.7 x 107 disintegrations per second

microcurie -µCi = 3.7 x 104 disintegrations per second

picocurie – pCi (or micro micro curie - µµCi) = 3.7 x 10-2 disintegrations per second = 2.22 disintegrations per minute.

decay (radioactive): Disintegration of the nucleus of an unstable nuclide by spontaneous emission of charged particles and/or photons.

decay constant: The probability of decay per unit time for a given radionuclide.

dose equivalent: Includes both the energy absorbed from a specific type of radiation and the general effectiveness of that radiation to cause biological damage.

dose rate: Absorbed dose delivered per unit time.

dosimeter: A small device used to detect and measure accumulated radiation exposure.

electron: A negatively charged particle with a mass of 9.1 x 10-28 grams.

electron capture (EC): A mode of radioactive decay involving the capture of an orbital electron by the nucleus followed by the emission of characteristic x-rays.

electron volt (eV): A unit of energy equivalent to the energy gained by an electron in passing through a potential difference of one volt. Larger multiple units of the electron volt are frequently used: keV for thousand or kilo electron volts; MeV for million or mega electron volts. One electron volt equals 1.6 x 10-12 erg.

erg: Unit of energy equal to 10-7 joules or 2.4 x 10-8 thermal calories.

excitation: The addition of energy to a system, resulting in an increase in the atomic or molecular energy level (without the removal of orbital electron).



gamma ray: Short wavelength electromagnetic emitted from the nucleus during radioactive decay; a photon.

gray: The international system of units for absorbed dose defined as one joule of energy absorbed per kilogram of material.

half-life (biological): The time required for the body to eliminate one-half of an administered dosage of any substance by regular processes of excretion. It is approximately the same for both stable and radioactive isotopes of a particular element.

half-life (effective): Time required for a radioactive element in an animal body to be diminished 50 percent as a result of the combined action of radioactive decay and biological elimination.

half-life (radioactive): Time required for 50% of the atoms to undergo radioactive decay within a sample of a given radionuclide.

half-value layer (HVL): The thickness of a specified substance which, when introduced into the path of a given beam of radiation, reduces the gamma ray intensity by 50%.

internal conversion: A form of radioactive decay where the decay energy normally seen as a gamma ray is imparted directly to an orbital electron. The electron is emitted with a discreet kinetic energy equal to the decay energy minus the binding energy of the electron.

inverse square law: For a point source of radiation, the dose rate is inversely proportional to square of the distance from the source.

ion chamber: Gas-filled radiation detection device with a relatively low voltage, which can be calibrated to measure dose or dose rate directly.

ion pair: An electron and positively charged ion created by the interaction of ionizing radiation with the atom.

ionization: The formation of one or more ions by the addition of electrons to or the removal of electrons from electrically neutral atoms. Ionization may be produced by radiation or through other physical and chemical interactions.

ionizing radiation: Electromagnetic or particulate radiation with sufficient energy to create ionization (produce ion pairs) in a material.

isobar: Nuclides having the same mass number but different atomic numbers, such as I-131 and Xe-131.

isometric transition: Radionuclide decay to a daughter which remains in an excited state for some time, perhaps minutes to hours. The excitation energy is later released as a gamma ray.



isotopes: Atoms having the same number of protons but different numbers of neutrons. Isotopes always share the same element name and atomic number.

linear absorption coefficient (µ): A factor expressing the fraction of a beam of x or gamma radiation absorbed in unit thickness of material.

mass absorption coefficient (µ/ρ): The linear absorption coefficient divided by the density of the material. It is frequently expressed in cm2 per gram.

monitoring: Periodic or continuous determination of the amount of ionizing radiation or radioactive contamination present in an occupied region.

neutrino: An electrically neutral particle of very small (probably zero) mass emitted during beta decay.

neutron: An electrically neutral or uncharged particle of matter in the nucleus with a mass of 1.67 x 10-24 grams (1.009 amu).

neutron number: The number of neutrons in an atom. Represented by the symbol N.

nucleon: Major categories of particles (protons and neutrons) within the nucleus of an atom.

nucleus: The dense, positively charged core of an atom, which accounts for most of the mass in an atom.

nuclide: A term used to denote any species of atom without reference to a particular element or grouping.

photoelectron: An electron ejected from an atom when all the energy of a photon is deposited in an inner shell electron.

photon: The basic packet of electromagnetic energy, generally regarded as having the properties of a wave as well as a particle. It has a discrete frequency but no charge or rest mass.

positron: A particle of the same mass (Me) as an electron, but has a positive (+1) charge. It is an antimatter electron.

proton: Elementary nuclear particle with a positive electric charge equal numerically to the charge of the electron and a mass of 1.67 x 10-24 grams (1.007 amu).

quality factor (Q): A factor expressing the relative effectiveness of a particular kind of radiation in producing biological damage.

rad: An energy deposition of 100 ergs per gram (or 0.01 joule per kilogram) of absorbing material

radionuclide: An atom having a combination of neutrons and protons which cause the nucleus to be unstable.

rem: Unit of dose equivalent equal to the number of rads (absorbed dose) times the quality factor (Q).



roentgen (R): A radiation unit, expressing ionization in air by x-rays or gamma rays. It is equal to the charge per unit mass produced in air. One roentgen equals 2.58 x 154 coulombs per kilogram of dry air.

shield: Material used to reduce the intensity from a source of radiation.

sievert (Sv): Unit of dose equivalent equal to the number of gray (absorbed dose) times the quality factor (Q). One sievert is equal to 100 rem.

specific gamma ray constant (Γ): The external radiation exposure rate per unit of activity at a fixed distance. It is often expressed in R/hr per mCi at one centimeter or in R/hr per Ci at one meter.

wavelength (λ): Distance between any two similar points of two consecutive waves. For electromagnetic radiation, the wavelength is equal to the velocity of light (c) divided by the frequency of the wave (λ), λ= c/v.

work function (W): The average energy required to produce an ion pair in a material. For air, it is about 33.7 eV.

x-rays: Photons similar to gamma rays which are produced by interactions outside the nucleis of atoms. These may be produced by transitions between orbital electron shells or by angular deceleration of electrons in a material.



Energy Units Multiply # of by to obtain # of

To obtain # of by divide # of

eV 1.6021 x 10-12 ergs eV 1.6021 x 10-19 joules (abs) eV 10-3 keV eV 10-6 MeV ergs 10-7 joules (abs) ergs 6.2419 x 105 MeV ergs 6.2419 x 1011 eV ergs 1.0 dyne-cm ergs 9.480 x 10-11 Btu ergs 7.376 x 10-8 ft-lb ergs 2.390 x 10-8 g-cal ergs 1.020 x 10-3 g-cm gm-calories 3.968 x 10-3 Btu gm-calories 4.184 x 107 ergs joules (abs) 107 ergs joules (abs) 0.7376 ft-lb joules (abs) 9.480 x 10-4 Btu g-cal/g 1.8 Btu/lb kg-cal 3.968 Btu kg-cal 3.086 x 103 ft-lb ft-lb 1.356 joules (abs) ft-lb 3.240 x 10-4 kg-cal kw-hr 2.247 x 1019 MeV kw-hr 3.60 x 1013 ergs MeV 1.6021 x 10-6 ergs eV 1.78253 x 10-33 grams of matter (equivalent) eV 1.07356 x 10-9 amu (equivalent) erg 1.11265 x 10-21 grams of matter (equivalent) proton masses 938.256 MeV of energy (equivalent) neutron masses 939.550 MeV of energy (equivalent) electron masses 511.006 keV of energy (equivalent) amu (on 12C scale) 931.478 MeV of energy (equivalent)



Radiological Units Multiply # of by to obtain # of

To obtain # of by divide # of

curies 3.700 x 1010 disintegrations per second (Bq) curies 2.220 x 1012 disintegrations per minute curies 103 millicuries curies 106 microcuries curies 109 nanocuries curies 1012 picocuries curies 10-3 kilocuries disintegrations per minute 4.505 x 10-10 millicuries disintegrations per minute 4.505 x 10-7 microcuries disintegrations per second (Bq) 2.703 x 10-8 millicuries disintegrations per second (Bq) 2.703 x 10-5 microcuries kilocuries 103 curies microcuries 3.700 x 104 disintegrations per second (Bq) microcuries 2.220 x 106 disintegrations per minute millicuries 3.700 x 107 disintegrations per second (Bq) millicuries 2.220 x 109 disintegrations per minute R 2.58 x 10-4 C/kg of air R 1.0 esu/cm3 of air (s.t.p.) R 2.082 x 109 ion pairs per cm3 of air (s.t.p.) R 1.610 x 1012 ion pairs per gram of air R (33.7 eV per ion pair) 7.02 x 104 MeV per cm3 of air (s.t.p.) R (33.7 eV per ion pair) 5.43 x 107 MeV per gram of air R (33.7 eV per ion pair) 86.9 ergs per gram of air R (33.7 eV per ion pair) 2.08 x 10-6 g-cal per gram of air R (33.7 eV per ion pair) ≈ 98 ergs per gram of soft tissue rads 0.01 Joule per kilogram rads 100 ergs per gram rads 8.071 x 104 MeV per cm3 of air (s.t.p.) rads 6.242 d 107 MeV per gram rads 10-5 watt-second per gram rad (33.7 eV per ion pair) 2.39 x 109 ion pairs per cm3 of air (s.t.p.) µCi per cm3 (µCi per ml) 2.22 x 1012 dpm per m3

µCi per cm3 2.22 x 109 dpm per liter



Hazard Information for Common Radionuclides

Hydrogen-3 (Tritium):

External Concerns Half-life 12.3 years Emission Beta (-) Maximum beta energy 0.019 MeV Average beta energy 0.006 MeV Beta range in tissue 0.0006 cm Fraction transmitted through dead layer of skin (0.007 cm) 0% Dose rate to basal cells of epidermis from 1 µCi/cm2 in contact with skin 0.0 mrad/hr

Method of detection Liquid scintillation counter Note: Not an external hazard. Internal Concerns Physical half-life 12.3 years Biological half-life 10 days Effective half-life 9.98 days Critical organ Body water (all organs) ALI 80 mCi Increased clearance Increased water intake Note: Many tritium compounds are volatile or can penetrate the skin. Tritiated

DNA precursors are considered more toxic than tritiated water, however, they are less volatile.



Carbon-14: External Concerns Half-life 5730 years Emission Beta (-) Maximum beta energy 0.156 MeV Average beta energy 0.049 MeV Beta range in tissue 0.028 cm

Fraction transmitted through dead 11% layer of skin (0.007 cm) Dose rate to basal cells of epidermis 1.4 rad/hr from 1 µCi/cm2 in contact with skin Method of detection Liquid scintillation counter

(GM has poor efficiency) Note: Millicurie quantities of C-14 should not present a significant external

exposure if gloves are worn, since the low-energy betas barely penetrate the combined thickness of the glove and the outer layer of skin.

Internal Concerns Physical half-life 5730 years Biological half-life few minutes to 35 days Effective half-life 10 days used as a conservative value Critical organ bone or fat ALI 2 mCi Note: Many C-14 compounds are rapidly metabolized and exhaled as CO2.

Some compounds are eliminated via the urine.



Sulfur-35:

External Concerns Half-life 88 days Emission Beta (-) Maximum beta energy 0.167 MeV Average beta energy 0.048 MeV Beta range in tissue 0.034 cm Fraction transmitted through 12% dead layer of skin (0.007) Dose rate to basal cells of epidermis 1.4 rad/hr from 1 µCi/cm in contact with skin Method of Detection Liquid scintillation counter

(GM has poor efficiency) Note: Millicurie quantities of S-35 should not present a significant external

exposure hazard if gloves are worn, since the low-energy betas barely penetrate the combined thickness of the glove and the outer layer of skin.

Internal Concerns Physical half-life 88 days Biological and effective half-lives Depends on chemical form. Some excreted rapidly; some remains for more than 2000 days. Critical organ Soft tissues ALI 10 mCi



Phosphorus-32: External Concerns

Half-life 14.3 days Emission Beta (-) Maximum beta energy 1.71 MeV Average beta energy 0.70 MeV Beta range in tissue 0.8 cm Fraction transmitted through 95% dead layer of skin (0.007 cm) Dose rate to basal cells of epidermis 9.2 rad/hr from 1 µCi/cm2 in contact with skin Method of detection GM counter or liquid scintillation counter Note: High energy betas can produce a substantial skin dose. Large quantities

of P-32 can present a significant bremsstrahlung hazard. Internal Concerns Physical half-life 14.3 days Biological and effective half-lives Complex. Some excreted rapidly; some retained permanently in bone. Critical organs Bones for soluble P-32, and lungs or intestines for inhaled or ingested non-soluble compounds. ALI 0.6 mCi



Phosphorus-33: External Concerns

Half-life 25.4 days Emission Beta (-) Maximum beta energy 0.249 MeV Average beta energy 0.075 MeV Beta range in tissue 0.06 cm Fraction transmitted through 40% dead layer of skin (0.007 cm) Dose rate to basal cells of epidermis 4 rad/hr from 1 µCi/cm2 in contact with skin Method of detection GM counter or liquid scintillation counter Note: Betas penetration can be significant. Moderate external hazard. Internal Concerns Physical half-life 25.4 days Biological and effective half-lives Complex. Some excreted rapidly; some retained permanently in bone. Critical organs Bones for soluble P-33, and lungs or intestines for inhaled or ingested non-soluble compounds. ALI 6 mCi (ingestion)



Iodine-125: External Concerns

Half-life 60 days Emission Electrons, gammas, x-rays Average electron energy 0.020 MeV Gamma 0.035 MeV (6.5%) X-rays 0.027 MeV (112%); 0.031 MeV (25.4%) R/hr per mCi at 1 cm (gamma) ~ 0.7 Half-value layer (lead) < 0.04 mm Method of detection Thin NaI (TI) crystal detector or liquid scintillation counter. GM counter has poor efficiency. Internal Concerns Physical half-life 60 days Biological half-life 120 days in thyroid; 12 days other body tissues Effective half-life 40 days in thyroid Critical organ Thyroid ALI 0.04 mCi Note: Elemental iodine and some iodine compounds are volatile. 25% to 30% of

ingested or inhaled iodine is taken up by thyroid.



Iodine-131: External Concerns Half-life 8.05 days Emission Beta (-), gamma Maximum beta energy 0.606 MeV (89%) Average beta energy 0.118 MeV Gammas 0.364 MeV (81%); others: 0.03 to 0.72 MeV (22%) R/hr per mCi at 1 cm 2.2 Dose rate to basal cells of epidermis 7.2 rad/hr from 1 µCi/cm2 in contact with skin Half-value layer (lead) 3 mm Method of detection GM, NaI (TI) detectors or liquid scintillation counter. Internal Concerns Physical half-life 8.05 days Biological half-life 120 days in thyroid; 12 days other body tissues Effective half-life 7.5 days in thyroid Critical organ Thyroid ALI 0.03 mCi Note: Elemental iodine and some iodine compounds are volatile. 25% to 30% of

ingested or inhaled iodine is taken up by the thyroid.



Appendix 1



Figure 1



Figure 2

Average and Maximum Beta Energy by Radionuclide

A = First excited state

Nuclide Energy in MeV Nuclide Energy in MeV Nuclide Energy in MeV

Average Maximum Average Maximum Average Maximum

N -1 0.301 --- C1-39 0.847 3.450 Ni-63 0.017 0.066

H -3 0.005 0.018 Ar-39 0.219 0.565 Cu-64 0.188 0.573

He-6 1.571 3.515 K -40 0.541 1.322 Ni-65 0.667 2.100

Be-10 0.229 0.555 Ar-41 0.479 2.515 Ni-66 0.064 0.224

C -14 0.049 0.158 K -42 1.446 3.559 Cu-66 1.062 2.630

C -15 2.871 9.775 K -43 0.301 1.838 Cu-67 0.146 0.577

O -19 1.708 4.601 Ca-45 0.076 0.254 Cu-68 1.284 3.000

O -20 1.242 2.850 Sc-46 0.112 1.465 Zn-69 0.324 0.913

F -20 2.486 5.403 Ca-47 0.341 2.000 Ga-70 0.644 1.650

F -21 2.624 5.683 Sc-47 0.160 0.601 Zn-71 0.921 2.240

Ne-23 1.903 4.372 Sc-48 0.220 0.643 Zn-71A 0.580 1.500

Ne-24 0.794 1.980 Ca-49 0.758 1.984 Zn-72 0.116 1.600

Na-24 0.553 4.170 Sc-49 0.826 2.011 Ga-72 0.429 3.166

Na-25 1.510 3.801 Sc-50 1.538 3.500 Ga-73 0.433 1.480

Na-26 3.124 6.700 Ti-51 0.870 2.142 Ga-74 1.021 4.300

Mg-27 0.689 1.763 V -52 1.069 2.532 As-74 0.405 1.355

Mg-28 0.155 0.457 V -53 1.068 2.530 Ga-75 1.425 3.300

A1-28 1.244 2.868 V -54 1.438 3.300 Ge-75 0.404 1.137

A1-29 1.034 2.500 Cr-55 1.220 2.850 Ga-76 2.741 6.000

A1-30 2.307 5.050 Cr-56 0.587 1.500 As-76 1.085 2.970

Si-31 0.588 1.476 Mn-56 0.860 2.850 Ge-77 0.637 2.270

Si-32 0.028 0.100 Mn-57 1.099 2.600 Ge-77A 1.198 2.880

P -32 0.694 1.709 Fe-59 0.116 1.560 As-77 0.221 0.684

P -33 0.076 0.248 Fe-60 0.069 0.240 Ge-78 0.317 0.900

P -34 2.075 5.100 Co-60 0.094 1.478 As-78 1.471 4.270

S -35 0.048 0.167 Co-60A 0.604 1.545 As-79 0.945 2.300

Cl-36 0.252 0.714 Fe-61 1.193 2.800 Se-79 0.058 0.158

S -37 0.795 4.750 Co-61 0.463 1.231 Br-80 0.748 2.000

S -38 0.463 3.000 Co-62 0.983 2.831 As-81 1.663 3.800

C1-38 1.515 4.924 Co-63 1.577 3.600 Se-81 0.531 1.400



Figure 2 continued




Br-82 0.137 0.444 Nb-94 0.156 0.500 Rh-107 0.425 1.201

Se-83A 1.379 3.400 Nb-94A 0.480 1.300 Pd-107 0.013 0.035

Br-83 0.335 0.960 Zr-95 0.115 1.130 Ru-108 0.466 1.320

Br-84 1.221 4.680 Nb-95 0.046 0.930 Rh-108 1.821 4.500

Br-84A 0.709 3.200 Y -96 1.507 3.500 Ag-108 0.624 1.650

Rb-84 0.582 1.648 Nb-96 0.244 0.707 Pd-109 0.359 1.025

Br-85 1.037 2.500 Zr-97 0.713 1.910 Ag-110 1.176 2.869

Kr-85 0.249 0.672 Nb-97 0.464 1.267 Ag-ll0A 0.070 0.530

Kr-85A 0.284 0.826 Tc-98 0.086 0.300 Pd-111 0.848 2.130

Rb-86 0.622 1.777 Nb-99 1.359 3.200 Ag-111 0.360 1.050

Br-87 1.872 8.000 Mo-99 0.398 1.215 Pd-112 0.078 0.277

Kr-87 1.334 3.800 Tc-YY 0.085 0.295 Ag-112 1.438 4.040

Rb-87 0.079 0.274 Nb-l00A 1.450 4.200 In-112 0.211 0.656

Kr-88 0.367 2.600 Mo-101 0.419 2.230 Pd-113 1.397 3.300

Rb-88 2.084 5.177 Tc-101 0.478 1.320 Ag-113A 0.787 2.000

Kr-89 1.395 3.920 Mo-102 0.436 1.200 Cd-113A 0.181 0.575

Rb-89 0.596 3.920 Tc-102 1.835 4.200 Pd-114 0.519 1.400

Sr-89 0.583 1.470 Tc-102A 0.792 2.000 Ag-114 2.018 4.600

Sr-90 0.200 0.544 Rh-102 0.144 0.470 In-114 0.776 1.984

Y -90 0.931 2.245 Tc-103 1.025 2.500 Ag-115 1.249 2.900

Kr-91 1.561 3.600 Ru-103 0.062 0.710 Cd-115 0.318 1.110

Rb-91 1.849 4.200 Tc-104 0.978 2.400 Cd-115A 0.605 1.631

Rb-91A 1.271 3.000 Rh-104 0.988 2.441 In-115 0.201 0.630

Sr-91 0.624 2.665 Rh-104A 0.451 1.240 In-115A 0.281 0.838

Y -91 0.615 1.548 Ru-105 0.415 1.870 Ag-116 2.211 5.000

Sr-92 0.213 1.500 Rh-105 0.167 0.563 In-116 1.387 3.290

Y -92 1.454 3.600 Ru-106 0.009 0.039 In-116A 0.294 1.000

Y -93 1.185 2.890 Rh-106 1.415 3.541 Cd-117A 0.348 1.000

Zr-93 0.015 0.063 Rh-106A 0.345 1.620 In-117 0.245 0.745

Y -94 2.368 5.320 Ru-107 1.637 4.008 In-117A 0.641 1.764




Figure 2 continued




Cd-118 0.267 0.800 Sb-128A 0.346 1.000 Cs-139 1.600 4.000

In-118 1.754 4.250 I -128 0.791 2.120 Ba-139 0.910 2.340

In-118A 0.560 1.500 Sb-129 0.729 1.870 Ba-140 0.282 1.010

In-119 0.605 1.600 Te-129 0.498 1.590 La-140 0.490 2.200

In-119A 1.061 2.650 I -129 0.040 0.150 Ba-141 1.158 2.833

In-120 0.876 2.200 I -130 0.276 1.020 La-141 0.958 2.430

In-121 1.202 2.900 Cs-130 0.132 0.442 Ce-141 0.144 0.580

In-121A 1.582 3.700 Te-131 0.723 2.141 La-142 1.823 4.250

Sn-121 0.111 0.383 Te-131A 0.183 2.457 Pr-142 0.829 2.153

Sn-121A 0.150 0.420 I -131 0.180 0.810 La-143 1.374 3.300

Sb-122 0.527 1.971 Te-132 0.047 0.220 Ce-143 0.371 1.380

In-123 1.391 3.300 I -132 0.512 2.920 Pr-143 0.314 0.933

In-123A 2.013 4.600 Te-133 0.964 2.400 Ce-144 0.081 0.320

Sn-123 0.455 1.260 Te-133A 0.567 2.400 Pr-144 1.208 2.984

Sn-123A 0.540 1.420 I -133 0.418 1.540 Ce-145 0.773 2.000

Sb-124 0.385 2.313 Xe-133 0.099 0.343 Pr-145 0.682 1.799

Sb-124A 1.340 3.200 I -134 0.663 2.410 Ce-146 0.224 0.700

Sb-124B 1.012 2.500 Cs-134 0.152 1.453 Pr-146 1.292 3.780

Sn-125 0.914 2.330 Cs-134A 0.170 0.550 Pm-146 0.233 0.725

Sn-125A 0.788 2.040 I -135 0.319 1.433 Nd-147 0.227 0.810

Sb-125 0.084 0.612 Xe-135 0.307 0.919 Pm-147 0.062 0.225

Sb-126 0.737 1.900 Cs-135 0.057 0.210 Pm-148 0.682 2.450

St-126A 0.737 1.900 Cs-136 0.108 0.657 Pm-148A 0.150 0.680

I -126 0.298 1.250 Xe-137 1.522 3.600 Nd-149 0.428 1.500

Sb-127 0.375 1.500 Cs-137 0.195 1.167 Pm-149 0.364 1.071

Te-127 0.223 0.695 Xe-138 0.961 2.400 Pm-150 0.762 3.122

Te-127A 0.263 0.730 Cs-138 1.095 3.400 Eu-150 0.309 1.070

Sb-128 0.199 2.900 La-138 0.056 0.205 Nd-151 0.617 1.995




Figure 2 continued




Average Maximum Average Maximum Average

Maximum

Pm-151 0.312 1.200 Er-169 0.096 0.340 W -188 0.256 0.800

Sm-151 0.019 0.077 Ho-170 1.257 3.100 Re-188 0.776 2.116

Pm-152 0.858 2.200 Tm-170 0.315 0.967 Re-189 0.237 0.750

Eu-152 0.288 1.840 Er-171 0.355 1.490 Re-190 0.556 1.700

Eu-152A 0.696 1.876 Tm-171 0.025 0.098 Re-191 0.661 1.800

Pm-153 0.614 1.650 Tm-172 0.511 1.830 Os-191 0.036 0.139

Sm-153 0.233 0.804 Tm-173 0.296 0.900 Ir-192 0.175 0.670

Pm-154 0.995 2.500 Tm-174 0.980 2.500 Ir-192A 0.431 1.500

Eu-154 0.228 1.850 Tm-175 0.757 2.000 Os-193 0.350 1.127

Sm-155 0.558 1.530 Yb-175 0.125 0.467 Ir-194 0.775 2.233

Eu-155 0.044 0.247 Tm-176 1.761 4.200 Os-195 0.746 2.000

Sm-156 0.175 0.730 Lu-176 0.104 0.362 Ir-195 0.297 1.000

Eu-156 0.425 2.447 Yb-177 0.465 1.380 Au-196 0.071 0.259

Tb-156A 0.037 0.140 Lu-177 0.140 0.497 Ir-197 0.642 2.000

Eu-157 0.366 1.270 Lu-178 0.886 2.300 Pt-197 0.303 0.670

Eu-158 0.060 2.650 Lu-178A 0.539 1.500 Ir-198 1.457 3.600

Tb-158 0.271 0.845 Lu-179 0.476 1.350 Au-198 0.315 1.371

Eu-159 0.855 2.200 Lu-180 1.339 3.300 Au-199 0.084 0.460

Gd-159 0.294 0.948 Ta-180A 0.201 0.705 Au-200 0.669 2.210

Eu-160 1.499 3.600 Hf-181 0.119 1.050 Au-201 0.519 1.500

Tb-160 0.189 1.700 Hf-182 0.149 0.500 Au-203 0.698 1.900

Gd-161 0.584 1.599 Ta-182 0.094 0.524 Hg-203 0.057 0.212

Tb-161 0.155 0.577 Hf-183 0.496 1.400 Tl-204 0.267 0.765

Ho-164 0.319 0.990 Ta-183 0.191 0.776 Hg-205 0.590 1.650

Dy-165 0.440 1.280 Ta-184 0.419 1.360 Tl-206 0.557 1.571

Dy-165A 0.275 0.840 Ta-185 0.624 1.718 Tl-207 0.503 1.441

Dy-166 0.060 0.400 W -185 0.124 0.427 Tl-208 0.562 2.380

Ho-166 0.610 1.852 Ta-186 0.838 2.200 Tl-209 0.733 1.990

Ho-166A 0.088 1.100 Re-186 0.941 1.066 Pb-209 0.195 0.637

Ho-168 0.716 1.900 W -187 0.236 1.307 Pb-210 0.005 0.161



Figure 2 continued



Average Maximum Average

Maximum Average Maximum

Bi-210 0.390 1.161 Ac-231 0.765 2.100 Np-240A 0.662 2.156

Pb-211 0.443 1.390 Th-231 0.059 0.305 Np-241 0.458 1.360

Bi-211 0.181 0.600 Th-233 0.410 1.230 Pu-241 0.005 0.021

Pb-212 0.106 0.586 Pa-233 0.063 0.568 Am-242 0.188 0.630

Bi-212 0.783 2.255 Th-234 0.046 0.193 Am-244 0.510 1.500

Pb-214 0.214 0.980 Pa-234 0.146 0.500 Am-244A 0.107 0.380

Fr-223 0.382 1.150 Pa-234A 0.515 1.500 Am-245 0.287 0.910

Ra-225 0.089 0.320 Np-236 0.476 1.400 Pu-246 0.053 0.330

Ac-226 0.400 1.200 Np-236A 0.149 0.518 Bk-248 0.194 0.650

Ra-227 0.444 1.310 U -237 0.067 0.248 Cm-249 0.282 0.900

Ac-227 0.010 0.043 Np-238 0.206 1.240 Bk-249 0.026 0.102

Ra-228 0.014 0.055 U -239 0.401 1.210 Cf-253 0.073 0.270

Ra-230 0.401 1.200 Np-239 0.135 0.723 Es-254A 0.331 1.040

Ac-230 0.807 2.200 U -240 0.101 0.360

Pa-230 0.117 0.410 Np-240 0.280 0.890


Source: O.H. Hogan, P. E. Zigman, and J. L. Mackin, II. Spectra of Individual Negatron Emitters (Beta Spectra, USNRDL-TR-802 [San Francisco: U.S. Naval Radiological Defense Laboratory, Dec. 16, 1964]).



Figure 3

Decay Schemes

Hydogen-3

0.0

He23Stable

H (12.3 y)

β− 100%

Q = 0.0186 MeVβ−

13

Carbon-14

0.0

N714Stable

β− 100%

Q = 0.1561 MeVβ−

C (5730y)614

0.0

N7

15Stable

O (124 s)815

QEC = 2.76 MeV *

* Maximum β+ Energy = QEC - 1.022 MeV

β+ 100%

Oxygen-15



Figure 3 continued

Fluorine-18

0.0

F (109.7 m)918

QEC = 1.655 MeV *

β+ 97%


O8

18Stable

EC 3%

Sodium-24

4.122

1.37

0.0

Stable Mg1224

γ2

1γ

-β 99+%

Na1124 (15.0 h)

Q = 5.51 MeVβ−



Figure 3 continued

Phosphorus-32

0.0

1532 P (14.3 d)

β− 100%

Stable S1632

Q = 1.710 MeVβ−

Phosphorus-33

0.0β− 100%

Stable S1633

P (25.4d)1533

Q = 0.248 MeVβ−

Sulfur-35

0.0

1635S (88 d)

β− 100%

Stable Cl1735

Q = 0.167 MeVβ−



Figure 3 continued

Calcium-45

0.0

Stable Sc2145

β− 100%

2045Ca (165 d)

Q = 0.252 MeVβ−

Chromium-51

0.3198

0.0

γ1

EC1 9%

QEC = 0.752 MeV

V2351Stable

EC2 91%

Cr (27.8 d)2451

Iron-55

Mn2555Stable

QEC = 0.232 MeV

Fe (2.6 y)2655

EC 100%0.0



Figure 3 continued

Cobalt-60

1.3325

0.0

γ1

γ2

2.5057

β1− 99+%

β2− 0.1%

2760 Co (5.26y)

Stable Ni2860

Q = 2.819 MeVβ−

Copper-64

Q = 0.573 MeV

QEC = 1.678 MeV *

β+ 19%

β - 38%

Stable Zn3064

Stable Ni2864

EC1 0.5%

EC2 43%

γ1

64 Cu (12.8 h)29


0.0

1.34

β−



Figure 3 continued

Zinc-65

QEC = 1.35 MeV*

1.115

3065 Zn (245 d)

Cu2965Stable

0.0

γ1

1β+ 1.7%

EC1 49%

EC2 49%


Strontium-90

0.0

9038 Sr (28.8 y)

β−100%

9039 Y (64 h)

(subsequent decay from Y-90 to Zr-90)

Q = 0.546 MeVβ−

Yttrium-90

0.0

Stable Zr

Q = 2.27 MeV

99+%β−1

Y (64 h)9039

9040

β−



Figure 3 continued

Molybdenum-99 and Technicium-99m

(2.12x105 y)

0.0γ1

0.922

1.11

0.513

Tc4399

0.1811

0.14270.1405

γ3γ4

γ7γ8

γ10

β−1 0.3%

IT

γ5 γ2

γ6

γ9

β− 17%2

β− 1.0%3

β− 82%4

(6.04h)Tc4399m

γ11

4299 Mo (67h)

Q = 1.37 MeVβ−

Indium-111

Stable Cd48111

0.419

0.0

γ1

γ2

0.247

EC 99+%

In (2.81 d)49

111

QEC = 1.1 MeV



Figure 3 continued

Iodine-125

0.0γ1

0.0355

I (60 d)53125

Stable Te52125

EC 100% QEC = 0.149 MeV

Iodine-131

0.7229

0.0γ1

γ2

0.6370

0.16390.0801γ3

γ4γ5

γ6

γ7γ8

γ9

β−1 1.6%

β−2 6.9%

0.5030β−

3 0.5%

β−4 90.4% 0.3645

0.1772β−5 0.6%

Xe (11.8 d) 54131m

XeStable 54131

53131I (8.05d)

Q = 0.970 MeVβ−

Cesium-137

0.0

0.6616

Cs (30.0y) 55137

Stable Ba56137

Ba (2.55 m)56137m

β−1 93.5%

β−2 6.5%

Q = 1.176 MeV

γ

β−



Figure 3 continued

Thallium-201

0.00160.0

γ40.03210.1674

γ2γ5 γ3 γ1

EC1 34%

EC2 8.0%

EC3 58%

QEC = 0.41 MeV

Tl (73 h)81201

Stable Hg80201

Radium-226

α1 5.4%α2 94.6%

Q = 4.894 MeV

Rn (3.82 d)86222

α

Ra (1602 y)88226

0.00.1857

γ



Figure 4

Radioactive Decay, Semi-Log Plot 0 to 7 Half-Lives



Figure 4 continued

Radioactive Decay, Semi-Log Plot 6 to 13 Half-Lives



Figure 5



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Environm

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Figure 5 continued



Figure 6



Figure 6 continued



Figure 7

Gamma Radiation Levels for One Curie of Some Radionuclides* Nuclide Γ† Nuclide Γ† Nuclide Γ† Actinium-227 ~2.2 Gold-198 2.3 Potassium-43 5.6 Antimony-122 2.4 Gold-199 ~0.9 Radium-226 8.25 Antimony-124 9.8 Hafnium-175 ~2.1 Radium-228 ~5.1 Antimony-125 ~2.7 Hafnium-181 ~3.1 Rhenium-186 ~0.2 Arsenic-72 10.1 Indium-114m ~0.2 Rubidium-86 0.5 Arsenic-74 4.4 Iodine-124 7.2 Ruthenium-106 1.7 Arsenic-76 2.4 Iodine-125 ~0.7 Scandium-46 10.9 Barium-131 ~3.0 Iodine-126 2.5 Scandium-47 0.56 Barium-133 ~2.4 Iodine-130 12.2 Selenium-75 2.0 Barium-140 12.4 Iodine-131 2.2 Silver-110m 14.3 Beryllium-7 ~0.3 Iodine-132 11.8 Silver-111 ~0.2 Bromine-82 14.6 Iridium-192 4.8 Sodium-22 12.0 Cadmium-115m ~0.2 Iridium-194 1.5 Sodium-24 18.4 Calcium-47 5.7 Iron-59 6.4 Strontium-85 3.0 Carbon-11‡ 5.9 Krypton-85 ~0.04 Tantalum-182 6.8 Cerium-141 0.35 Lanthanum-140 11.3 Tellurium-121‡ 3.3 Cerium-144 ~0.4 Lutecium-177 0.09 Tellurium-132 2.2 Cesium-134 8.7 Magnesium-28 15.7 Thulium-170 0.025 Cesium-137 3.3 Manganese-52 18.6 Tin-113 ~1.7 Chlorine-38‡ 8.8 Manganese-54 4.7 Tungsten-185 ~0.5 Chromium-51 0.16 Manganese-56 8.3 Tungsten-187 3.0 Cobalt-56 17.6 Mercury-197 ~0.4 Uranium-234 ~0.1 Cobalt-57 0.9 Mercury-203 1.3 Vanadium-48 15.6 Cobalt-58 5.5 Molydenum-99 ~1.8 Xenon-133 0.1 Cobalt-60 13.2 Neodymium-147 0.8 Ytterbium-175 0.4 Copper-64 1.2 Nickel-65 ~3.1 Yttrium-88 14.1 Europium-152 5.8 Niobium-95 4.2 Yttrium-91 0.01 Europium-154 ~6.2 Osmium-191 ~0.6 Zinc-65 2.7 Europium-155 ~0.3 Palladium-109 0.03 Zirconium-95 4.1 Gallium-67 ~1.1 Platinum-197 ~0.5 Gallium-72 11.6 Potassium-42 1.4 * Jaeger, R. G., et al., Engineering Compendium on Radiation Shielding, Vol. 1, (New

York: Springer-Verlag, 1968), pp. 21-30. † Γ = R-cm2/hr-mCi or Γ/10 = R/hr at 1 m/Ci ‡ A Manual of Radioactivity Procedures (National Bureau of Standards Handbook No. 80

[Washington, D.C.: Supt. Of Docs., U.S. Government Printing Office, Nov. 1961], Appendix A, pp. 137-140.



Figure 8

Specific Gamma Ray Constants for Monoenergetic Photons



Figure 9



Figure 10



Figure 11

Beta Emitters

UW

Column 2: The contamination level maintained on the skin for a 24 hour day to deliver 0.5 rem/year to the basal layer. Multiply by 17.52 to get level which gives 1 mrem/hour. For a single event during the year, the initial level requiredto deliver 0.5 rem in the following year can be higher by a factor of 17 [1 + (15/T1/2)] where T1/2 is the radioactive half-life of the radionuclide in days. Column 3: The contamination distributed through a clothing thickness of 23 mg/cm2 to deliver an annual dose of 0.5 rems to the basal layer of the skin if the clothing is worn continuously.

(2) (3) (2) (3) Radio- nuclide

Skin Dose

Clothing Dose

Radio- nuclide

Skin Dose

Clothing Dose

nCi / cm2 nCi / cm2

Beta Emitters Rb-87 0.010 0.060 C-14 0.040 0.400 Sr-89 0.007 0.009 Na-22 0.007 0.010 Sr-90 0.008 0.020 P-32 0.007 0.007 Y-90 0.007 0.009 S-35 0.040 0.400 Y-91 0.007 0.009 Cl-36 0.007 0.010 Zr-95 0.009 0.020 Ca-45 0.020 0.070 Nb-95 0.030 0.200 Ca-47 0.007 0.010 Mo-99 0.007 0.009 Sc-46 0.009 0.020 Tc-99 0.010 0.050 Sc-47 0.008 0.010 Ru-103 0.020 0.100 Sc-48 0.007 0.010 Ru-106 0.007 0.010 V-48 0.010 0.020 Rh-105 0.008 0.020 Mn-52 0.020 0.020 Ag-110m 0.020 0.300 Fe-59 0.008 0.010 Ag-111 0.007 0.010 Co-58 0.040 0.080 Cd-115m 0.007 0.009 Co-60 0.010 0.030 Cd-115 0.007 0.010 Ni-65 0.007 0.008 In-114m 0.007 0.009 As-74 0.010 0.010 In-115 0.008 0.020 As-76 0.007 0.009 Sn-125 0.007 0.009 As-77 0.007 0.010 Sb-122 0.007 0.008 Br-82 0.008 0.020 Sb-124 0.006 0.008 Rb-86 0.007 0.009 Sb-125 0.007 0.010

Environmental Health and Safety


Figure 11 continued

(2) (3) (2) (3) Radio- nuclide

Skin Dose

Clothing Dose

Radio- nuclide

Skin Dose

Clothing Dose

nCi / cm2 nCi / cm2

Beta Emitters continued Electron Capture and Internal Transition Decay

Te-127m 0.007 0.010 Cr-51 1.000 Te-129m 0.007 0.010 Mn-54 0.200 Te-131m 0.008 0.008 Fe-55 1.000 Te-132 0.005 0.007 Co-57 0.600 I-126 0.010 0.020 Ni-59 0.400 I-129 0.020 0.100 Zn-65 0.200 I-131 0.007 0.010 Ge-71 0.900 Cs-134 0.008 0.020 As-73 0.900 Cs-135 0.020 0.100 Se-75 0.300 Cs-136 0.010 0.030 Sr-85 0.300 Cs-137 0.008 0.020 Tc-96 0.070 Ba-140 0.007 0.010 Tc-97 1.000 La-140 0.006 0.010 Ru-97 0.500 Ce-141 0.008 0.020 Pd-103 1.000 Ag-105 0.400 Cd-109 0.700 Sn-113 0.500 Cs-131 1.000 Ba-131 0.400 Gd-153 1.000 W-181 2.000



Figure 12



Figure 13

Annual Limits on Intake (ALI) for Occupational Exposures

Lung Clearance Class: D (days) W (weeks) Y (years)

Nuclide

(Half-life) Inhalation Limit

µCi (MBq)

Form Lung Class

Ingestion Limit µCi (MBq)

Form

3H [tritium]

(12.35 y)

80,000 (3000) Water vapor -- 80,000 (3000) All forms

14C (5730 y)

2000 (90) 2 x 105 (60,000) 2 x 106 (8,000)

Organic forms Monoxides Dioxides

-- 2000 (90) Organic forms

32 P (14.29 d)

400 (10) 900 (30)

Phosphates All others

W D

600 (20) All forms

33 P (25.4 d)

3000 (100) 8000 (300)

Phosphates All others

W D

6000 (200) All forms

35 S (87.44 d)

20,000 (600) 2000 (80) 10,000 (500)

Sulfates & Sulfides Elemental Vapor (gases)

D W --

10,000 (400) 6000 (200)

Inorganic forms Elemental

45 Ca (163 d)

800 (30) All forms W 2000 (60) All forms

51 Cr (27.7 d)

20,000 (700) 20,000 (900) 50,000 (2000)

Oxide & hydroxide Halides & nitrates All others

Y W D

40,000 (1000) 40,000 (1000)

Trivalent state Hexavalent state

59 Fe (44.53 d)

500 (20) 300 (10)

Oxide, hydroxide & halides All others

W

D

800 (30) All forms

64Cu (12.7 h)

20,000 (800) 20,000 (900) 30,000 (1000)

Oxide & hydroxide Sufites, halides &nitrates All others

Y W

D

10,000 (400) All forms

65 Zn (243.9 d)

300 (10) All forms Y 400 (10) All forms

67 Ga (78.26 h)

10,000 (400) 10,000 (500)

Oxide, hydroxide, carbides, halides, nitrates All others

W

D


85 Sr (64.84 d)

2000 (60) 3000 (100)

SrTiO3

All others Y D

3000 (90) 4000 (100)

Soluble salts SrTiO3


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Figure 13 continued

Nuclide

(Half-life) Inhalation Limit

µCi (MBq)

Form Lung Class

Ingestion Limit µCi (MBq)

Form

99mTc (6.02 h)

2 x 105 (9000) 2 x 105 (6000)

Oxide, hydroxide, halides & nitrates All others

W

D

80,000 (3000) All forms

99 Mo (66 h)

1000 (50) 3000 (100)

Oxide, hydroxide & MoS2

All others

Y

D

1000 (40) 2000 (60)

MoS2 All others

109 Cd (464 d)

100 (4) 100 (4) 40 (1)

Oxide & hydroxide Sulfates, halides & nitrates All others

Y W

D

300 (10) All inorganic forms

111 In (2.83 d)

6000 (200) 6000 (200)

Oxide, hydroxide, halides & nitrates All others

W

D


115m Cd (44.6 d)

100 (5) 100 (5) 50 (2)

Oxide & hydroxide Sulfates, halides & nitrates All others

Y W

D

300 (10) All inorganic forms

123 I (13.2 h)

6000 (200) All forms D 3000 (100) All forms

125 I (60.14 d)


131 I (8.04 d)


192 Ir (74.02 d)

200 (8) 400 (10) 300 (10)

Oxide & hydroxide Halides, nitrates & metallic form All others

Y W

D

900 (40) All forms

Radiation Exposure from Consumer Products and Miscellaneous Sources

Source

No. of People

Exposed in the United

States

Average Annual Dose Equivalent to the Exposed Population

Remarks

Average Annual

Population Dose

Equivalent

Remarks

Unwanted Byproduct X Rays

Television Receivers 100,000,000

0.7-1.5 mrem (male) 0.2-0.4 mrem (female)

0.5 mrem

Gonadal dose equivalent

Cold Cathode Gas Discharge Tubes

< 500,000 < 1 mrem Primarily high school students < 2.5 urem Gonadal dose equivalent

Electron Microscopes 4,400 50 mrem Ranges from 50-200 mrem/y Whole-body dose equivalent

2-10 urem Whole-body dose equivalent

Intentional X Rays Airport Inspection Systems Personnel Scanning Systems Shoe-Fitting Fluoroscopes

10,000,000 Unknown Very small

22 :rem 0.25-800 mrem 30-170 mrem per exposure

Gonadal dose equivalent Gonadal dose equivalent Pelvic exposure

1 u:rem Unknown Unknown

Gonadal dose equivalent

Processed Radioactive Materials

Radioluminous Products Luminous Wristwatches Pocket Watches Clocks Aircraft Instruments

10,000,000 16,000,000 2,000,000 20,000 20,000,000 10,000,000 Unknown

3 mrem 0.6 mrem < 1 mrem 6 mrem < 1 mrem < 7-9 mrem 1-5 rem

226Ra gonadal dose equivalent 3H whole-body dose equivalent 147Pm gonadal dose equivalent 226Ra gonadal dose equivalent 3H or 147Pm whole-body dose equivalent 226 Ra whole-body dose equivalent 226Ra dials from World War II aircraft, whole-body

150 :rem 50 :rem < 10 urem ~ 0.5 urem < 100 urem

~ 0.3-0.5

mrem

Unknown

226Ra gonadal dose equivalent 3H whole-body dose equivalent 147Pm gonadal dose equivalent Gonadal dose equivalent Whole-body dose equivalent Whole-body dose equivalent

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Source

No. of People

Exposed in the United States

Average Annual Dose Equivalent to the Exposed

Population

Remarks

Avg Annual Population

Dose Equivalent

Remarks Processed Radioactive Materials Check Sources Static Eliminators Spark Gap-Irradiators Gas and Aerosol Detectors

800,000 100,000 Very small 10,000,000

1-100 mrem 1 µrem < 0.1 mrem 0.03-1.5 mrem

Whole-body dose equivalent Whole-body dose equivalent Gonadal and whole-body dose equivalent to user Whole-body dose equivalent

4-400 µrem <<< 1 µrem < 10 µrem 1-45 µrem

Whole-body dose equivalent Whole-body dose equivalent Whole-body dose equivalent Whole-body dose equivalent

Personnel Dosimeters Containing Thorium: Dosimeter Distributors and Handlers Dosimeter Wearers Detector Replacers Radiator Disposers Identification Cards

375 150,000 375 Several None

0.2 mrem 1.3 mrem 0.1 mrem 0.0002 mrem 0-25 urem

Whole-body dose equivalent for 20 year old thorium Presently used outside U.S.A. Whole-body dose equivalent

0.1 mrem 22 u:rem 0 u:rem

Whole-body dose equivalent Gonadal dose equivalent

Natural Radioactive Materials Tobacco Products Building Materials Highway and Road Construction Materials

50,000,000 100,000,000 5,000,000

8 rem 7 mrem 4 mrem

Maximum estimated dose equivalent to small areas of the bronchial epithelium at segmental bifurcations Whole-body dose equivalent; does not include lung irradiation from 222Rn daughters Gonadal dose equivalent

2 rem 3.5 mrem 0.1 mrem

Bronchial epithelial dose equivalent Whole-body dose equivalent Gonadal dose equivalent

Natural Radioactive Materials

Combustible Fuels Coal Oil

50,000,000 18,000,000

0.25-4 mrem 2-40 :rem

Lung dose equivalent Lung dose equivalent to people exposed within a radius of 10 miles of an oil-burning plant

0.5-1 mrem < 4 :rem

Lung dose equivalent Lung dose equivalent

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Source

No. of People Exposed in the United

States

Average Annual Dose Equivalent to the Exposed Population

Remarks

Avg Annual Population

Dose Equivalent

Remarks

Natural Radioactive Materials Natural Gas Cooking Ranges Unvented Heaters

125,000,000 16,000,000

6-9 mrem 22 mrem

Bronchial epithelial dose equivalent Bronchial epithelial dose equivalent

5 mrem 2 mrem

Bronchial epithelial dose equivalent Bronchial epithelial dose equivalent

Natural Gas (Nuclear Stimulated)

None < 1 mrem (projected)

This whole-body dose equivalent is in addition to that received from non-nuclear stimulated natural gas

0 mrem Whole-body dose equivalent

Glass and Ceramics Uranium in Dental Porcelain

(Dentures and Crowns)

Ophthalmic Glass (Eyeglasses)

45,000,000 Unknown

60 rem << 1 rem ~ 0.1 rem 1-4 rem

Delivered to the superficial layers of tissue in contact with these teeth and subject to alpha radiation Delivered from the uranium beta radiation Delivered from the potassium-40 beta radiation Delivered to germinal cells of the cornea, assuming glass is in compliance with federal regulations

10-15 rem <<0.25 rem ~ 0.02 rem Unknown

Basal mucosal dose equivalent Basal mucosal dose equivalent Basal mucosal dose equivalent

Miscellaneous Exposure Sources High Voltage Vacuum Switches Contaminated Raw Materials Aircraft Transport of Radioactive Materials

40,000 Very small 6,000,000

< 30 mrem Up to thousands of rem 0.2 mrem

Gonadal dose equivalent. Higher doses are predicted for those who test these devices; see text Dose is highly localized Whole-body dose equivalent

6 :rem Unknown 7 :rem

Whole-body dose equivalent Whole-body dose equivalent

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