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Chapter 19Radioactivity and Nuclear Chemistry
Roy KennedyMassachusetts Bay Community College
Wellesley Hills, MA
Chemistry: A Molecular Approach, 2nd Ed. By Nivaldo Tro
Copyright 2011 Pearson Education, Inc.
The Discovery of Radioactivity
2
• Phosphorescence is the long-lived emission of light by atoms or molecules that sometimes occurs after they absorb light
• Antoine-Henri Becquerel designed an experiment to determine if phosphorescent minerals gave off X-rays
Becquerel observed that only some phosphorescent materials produced penetrating rays
While certain other minerals were constantly producing energy rays that could penetrate matter
The rays behaved like X-rays
He determined that all minerals that contained uranium produced “uranic rays” even though the minerals were not exposed to outside energy
The Discovery of RadioactivityMarie Curie
3
• X-rays were detected by their ability to penetrate matter and expose a photographic plate
• Marie Curie broke down the minerals and used an electroscope to detect the source of the uranic rays
she found that rays were emitted from uranium and other elements
Some of which were new elements, e.g. radium named for its green
phosphorescence polonium named for her homeland, Poland.
• Because the rays were no longer just a property of uranium, she called the rays radioactivity
Electroscope++
+ +++
When a positive charge is induced on the metal foils, they
spread apart due to+ charge repulsion
When a substance producing ionizing
radiation is placed in the flask, the radiation knocks
electrons off the air molecules and onto the + charged foils. As a result,
the + charge is discharged, allowing the two foils to come back
together4
Other Properties of Radioactivity
5
• Radioactive rays can ionize matter, andcan cause uncharged matter to become charged
basis of Geiger Counter and electroscope
• Radioactive raysare high energycan penetrate mattercan cause chemicals to phosphoresce
basis of scintillation counter
What Is Radioactivity?
• Radioactivity is the release of tiny, high-energy particles or gamma rays from an atom
• Particles are ejected from the nucleus
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Types of Radioactive Decay
7
• Rutherford discovered three types of rays
alpha () rays charge +2 c.u. (charge units) mass 4 amu helium nucleus
beta () rays Charge −1 c.u. negligible mass electron-like
gamma (rays light energy not a particle like andrays
Rutherford’s Experiment
++++++++++++
--------------
8
• Positively charged particle attracted to the – plate• Travels further, deflected more slowly, higher mass
• Negatively charged particle attracted to the + plate• Deflected quickly, low mass
• Gamma ray, not deflected by charged plates• Light energy, not particle
Types of Radioactive Decay
9
In addition, some unstable nuclei can
• Emit Positrons a positively charged electron
• Undergo Electron capture low energy electron pulled into the nucleus
Penetrating Ability of Radioactive Rays
0.01 mm 1 mm 100 mm
Pieces of Lead
10
Facts About the Nucleus•Volume of the atom >> than volume of nucleus
•Entire mass of atom in the nucleus
•Nucleus is very dense
•Composed of nucleons (protons and neutrons) that are tightly held together
•Every atom of an element has the same number of protons = the atomic number (Z)
•Atoms of the same elements can have different numbers of neutrons, therefore different atomic masses, isotopes
• Isotopes are identified by their mass number (A)mass number = number of protons + neutrons
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# protons = Zatomic mass = A
# neutrons = A – Z
Radioactivity
• The nucleus of an isotope is called a nuclideAll nuclides with 84 or more protons are radioactive
>90% of known nuclides are radioactive, i.e. radionuclides which are unstable and decompose radioactive decay, which involves the nuclide emitting a
particle and/or energy
• The radioactive nucleus, the parent nuclide, spontaneously decomposes into smaller nucleus, the daughter nuclide
• Each nuclide is identified by a symbol
12
Important Atomic Symbols
13
Transmutation
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• Rutherford discovered that during the radioactive process, atoms of one element are changed into atoms of a different element – transmutationshowing that statement 3 of Dalton’s Atomic Theory is
valid only for chemical reactions, but not for nuclear chemistry
• For one element to change into another, the number of protons in the nucleus must change!
Chemical Processes vs. Nuclear Processes
• Chemical reactions involve changes in the electronic structure of the atomatoms gain, lose, or share electronsno change in the nuclei occurs
• Nuclear reactions involve changes in the structure of the nucleuswhen the number of protons in the nucleus
changes, the atom becomes a different element
15
Nuclear Equations
• We describe nuclear processes with nuclear equations
• Use the symbol of the nuclide’s element to represent the nucleus
• Atomic (Z) and the mass numbers (A) are conserved the mass # (A) of the daughter nuclide + A of the emitted
particle must = that of the parent nuclide the atomic number (Z) of the daughter nuclide + Z of the
emitted particle must equal that of the parent nuclide
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Alpha Emission
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88222Ra
24He
86218Rn
• An particle contains 2 protons and 2 neutrons = helium nucleus
• Most ionizing, but least penetrating of the types of radioactivity
• Loss of an alpha particle meansatomic number, Z, decreases by 2mass number, A, decreases by 4
Beta Emission
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• A particle is like an electronmoving much fasterproduced from the nucleus
• ~10 times more penetrating than the particle, but only about half the ionizing ability
• When an atom loses a particle itsatomic number increases by 1 (+1 proton, -1 neutron)mass number remains the same
• In beta decay, a neutron changes into a proton
Gamma Emission
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• Gamma () rays are high energy photons of light
• No loss of particles from the nucleus• No change in the composition of the nucleus
same atomic number and mass number• Least ionizing, but most penetrating• Generally occurs after the nucleus undergoes
some other type of decay and the remaining particles rearrange
Positron Emission
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• Positron’s have a charge of +1 c.u. and negligible massanti-electron
• Similar to beta particles in their ionizing and penetrating ability
• When an atom loses a positron from the nucleus, itsmass number remains the sameatomic number decreases by 1
• Positrons result from a proton changing into a neutron
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Electron Capture
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• Occurs when an inner orbital electron is pulled into the nucleus
• No particle emission, but atom changessame result as positron emission
• Proton combines with the electron to make a neutronmass number stays the sameatomic number decreases by one
Particle Changes
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What Kind of Decay and How Many Protons and Neutrons Are in the Daughter?
Alpha emission giving a daughter nuclide withnine protons and seven neutrons
11 p+
9 n0
25
= proton
= neutron
? +
? +
What Kind of Decay and How Many Protons and Neutrons Are in the Daughter?,
Continued
Beta emission giving a daughter nuclide with10 protons and 11 neutrons
9 p+
12 n0
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= proton
= neutron
= electron
What Kind of Decay and How Many Protons and Neutrons Are in the Daughter?,
Continued
Positron emission giving a daughter nuclide withfour protons and five neutrons
5 p+
4 n0
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? +
= proton
= neutron
= positron
Nuclear Equations
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• In the nuclear equation, mass numbers and atomic numbers are conserved
• We can use this fact to determine the identity of a daughter nuclide if we know the parent and mode of decay
Example 19.2b: Write the nuclear equation for positron emission from K–40
1. Write the nuclide symbols for both the starting radionuclide and the particle
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Examle 19.2b: Write the nuclear equation for positron emission from K–40
2. Set up the equation• emitted particles are products
• captured particles are reactants
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Example 19.2b: Write the nuclear equation for positron emission from K–40
3. Determine the mass number and atomic number of the missing nuclide
• mass and atomic numbers are conserved
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Example 19.2b: Write the nuclear equation for positron emission from K–40
4. Identify and determine the symbol of the element with atomic number 18
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Write a nuclear equation for the following
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alpha emission from U–238
beta emission from Ne–24
positron emission from N–13
electron capture by Be–7
What Causes Nuclei to Decompose? N/Z Ratio
• Nucleons are held together by a very strong attractive force only found in the nucleus called the strong forceOnly acts over very short distances
• Neutrons add to the strong force and stabilize the nucleusbut don’t repel each other like the protons
• The neutron : proton ratio is an important measure of the stability of the nucleus If N/Z is too high, neutrons are converted to protons via
decay If N/Z is too low, protons are converted to neutrons via
positron emission or electron capture or via decay – though not as efficiently
34
Valley of Stability
for Z = 1 20, stable N/Z ≈ 1
for Z = 20 40, stable N/Z approaches 1.25
for Z = 40 80, stable N/Z approaches 1.5
for Z > 83, there are no stable nuclei
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Example 19.3b: Predict the kind of radioactive decay that Mg−22 undergoes
• Mg–22Z = 12N = 22 – 12 = 10
• N/Z = 10/12 = 0.83• From Z = 1 20, stable
nuclei have N/Z ≈ 1• Because Mg–22 N/Z is
low, it should convert p+ into n0, therefore it will undergo positron emission or electron capture
36
Predict whether Kr–85 is stable or radioactive. If radioactive, predict the mode of radioactive
decay and the daughter nuclide.Kr–85 has Z = 36 and N = (85 − 36) = 49
Because the N/Z ratio of Kr–85 is greater than 1.25, it has too many neutrons and will undergo decay to reduce them
Because most stable isotopes with Z between 20 and 40 have N/Z ratios between 1 and 1.25, we expect Kr–85 to be radioactive
(Kr–85 is a byproduct of nuclear fission and was released into the atmosphere when atom bombs were tested in the 1940’s to 1960’s)
37
Magic Numbers• The N/Z ratio is important for nuclear stability, however the
actual numbers of protons and neutrons affects stability Most stable nuclei have even numbers of protons and neutrons Only a few have odd numbers of protons and neutrons
• If the total number of nucleons adds to a magic number, the nucleus is more stable same principle as stability of the
noble gas electron configuration Magic numbers are when
N or Z = 2, 8, 20, 28, 50, 82; or N = 126 most stable
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Decay Series
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• Often, one radioactive nuclide changes into another radioactive nuclide i.e. the daughter nuclide is also radioactive
• When radioactive nuclides are produced one from another, until a stable nuclide is made, we call this a decay series
• To determine the stable nuclide at the end of the series without writing it all out
1. count the number of and decays
2. from the mass no. subtract 4 for each decay
3. from the atomic no. subtract 2 for each decay and add 1 for each
U-238 Decay Series
or
or other combinations
40
Detecting RadioactivityTo detect something, you need to identify what it does
• Radioactive rays can expose light-protected photographic film
• Therefore, photographic film can be used to detect the presence of radioactive rays – film badge dosimeters
41
• Radioactive rays cause air to become ionized• An electroscope detects radiation by its ability to
penetrate the flask and ionize the air inside• A Geiger counter works by counting electrons
generated when Ar gas atoms are ionized by radioactive rays
Detecting Radioactivity• Radioactive rays cause certain chemicals to
give off a flash of light when they strike the chemical
• A scintillation counter is able to count the number of flashes per minute
42
Natural Radioactivity• There are small amounts of radioactive
minerals in the air, ground, water, and even in the food you eat!
• The radiation you are exposed to from natural sources is called background radiation
Rate of Radioactive Decay
43
• The rate of change in the amount of radioactivity is constant, and different for each radioactive “isotope”change in radioactivity measured with a Geiger counter
• Each radionuclide had a particular length of time required to lose half its radioactivity a constant half-life, which means it follows first order
kinetic rate laws
• The rate of radioactive change is not affected by temperaturemeaning radioactivity is not a chemical reaction!
Kinetics of Radioactive Decay• Rate = kNN = number of radioactive nuclei
• t1/2 = 0.693/ka shorter half-life means that more nuclei decay every second – the sample is hotter
44
Nuclide Half-Life Type of Decay
Th–232 1.4 x 1010 yr alpha
U–238 4.5 x 109 yr alpha
C–14 5730 yr beta
Rn–220 55.6 sec alpha
Th–219 1.05 x 10–6 sec alpha
Half-LifeHalf of the radioactive atoms decay each half-life
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Example19.4: If you have a 1.35 mg sample of Pu–236, calculate the mass that will remain after 5.00 years
47
units are correct, the magnitude makes because since it is less than ½ the original mass for longer than 1 half-life
Check:
Solve:
Conceptual Plan:
Relationships:
mass Pu–236 = 1.35 mg, t = 5.00 yr, t1/2 = 2.86 yr
mass remaining, mg
Given:
Find:
t1/2 k m0, t mt+
48
If there is 10.24 g of Rn–222 in the house today, how much will there be in 5.4 weeks?
units are correct, the magnitude makes sense because the length of time is 10 half-lives
Check:
Solve:
Conceptual Plan:
Relationships:
mass Rn–222 = 10.24 g, t = 5.4 wks, t1/2 = 3.8 d
mass remaining, g
Given:
Find:
t1/2 k m0, t mt+
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Radiometric Dating
50
• The change in radioactivity of a particular radionuclide is predictable and not affected by environmental factors
By measuring and comparing the amount of a parent radioactive isotope and its stable daughter we can determine the age of the object by using the half-life and the previous equations
• Mineral (geological) datingcomparing the amount of U-238 to Pb-206 in volcanic rocks
dates the Earth to between 4.0 and 4.5 billion yrs. old
Radiocarbon Dating• All things that are alive or were once alive contain carbon
• Three isotopes of carbon exist in nature, one, C–14, is radioactive and has a half-life = 5730 yrs
• We would normally expect a radioisotope with this relatively short half-life to have disappeared long ago, but atmospheric chemistry keeps producing C–14 at nearly the same rate it decays
Radiocarbon Dating
51
• While an organism is living, C–14/C–12 is constant because the organism replenishes its supply of carbonCO2 in air ultimate source of all C in organisms
• Once the organism dies the C–14/C–12 ratio decreases due to radioactive decay
• By measuring the C–14/C–12 ratio in a once living artifact and comparing it to the C–14/C–12 ratio in a living organism, we can tell how long ago the organism died
• The limit for this technique is 50,000 years oldabout 9 half-lives, after which radioactivity from C–14
will be below the level of background radiation
Radiocarbon Dating% C-14 (compared to living
organism)Object’s Age (in years)
100% 0
90% 870
80% 1850
60% 4220
50% 5730
40% 7580
25% 11,500
10% 19,000
5% 24,800
1% 38,10052
Example 19.5: An ancient skull gives 4.50 dis/min∙gC. If a living organism gives 15.3 dis/min∙gC, how old is the skull?
53
units are correct, the magnitude makes sense because it is less than 2 half-lives
Check:
Solve:
Conceptual Plan:
Relationships:
ratet1/2 = 4.50 dis/min∙gC, ratet1/2 = 15.3 dis/min∙gC
time, yr
Given:
Find:
t1/2 k rate0, ratet t+
54
units are correct, the magnitude makes sense because it is between 10 and 25% of the original activity
Check:
Solve:
Conceptual Plan:
Relationships:
t = 15,600 yr, rate0 = 20.0 counts/min∙gC
ratet, counts/min∙gC
Given:
Find:
t1/2 k rate0, t ratet+
Archeologists have dated a civilization to 15,600 yrs ago. If a living sample gives 20.0 counts per minute per gram C, what
would be the number of counts per minute per gram C for a rice grain found at the site?
Nonradioactive Nuclear Changes
Lise Meitner
55
• A few nuclei are so unstable that if their nucleus is hit just right by a neutron, the large nucleus splits into two smaller nuclei — this is called fission
• Small nuclei can be accelerated to such a degree that they overcome their charge repulsion and smash together to make a larger nucleus - this is called fusion
• Both fission and fusion release enormous amounts of energy
fusion releases more energy per gram than fission
Fission Chain Reaction
56
• A chain reaction occurs when a reactant in the process is also a product of the processin the fission process it is the neutronsso you only need a small amount of neutrons to start
the chain
• Many of the neutrons produced in fission are either ejected from the uranium before they hit another U-235 or are absorbed by the surrounding U-238
• The minimum amount of fissionable isotope needed to sustain the chain reaction is called the critical mass
57
Fission
Fissionable Material
58
• Fissionable isotopes include U–235, Pu–239, and Pu–240
• Natural uranium is mostly U – 238 and less than 1% U–235 Not enough U–235 to sustain a fission chain
reaction
• To produce fissionable uranium, the natural uranium must be enriched in U–235 to ~7% for “weapons grade” ~3% for reactor grade
Nuclear Power Plants vs. Coal-Burning Power Plants
• Use about 50 kg of fuel to generate enough electricity for 1 million people
• No air pollution
• Use about 2 million kg of fuel to generate enough electricity for 1 million people
• Produce NO2 and SOx that add to acid rain
• Produce CO2 that adds to the greenhouse effect
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• Nuclear reactors use fission to generate about 20% of U.S. electricity, utilizing the heat produced by the fission of U–235 to boil water, creating steam, and using it to turn a turbine to generate electricity
Nuclear Power Plants
60
• The fissionable material is stored in long tubes, called fuel rods, arranged in a matrix
• Between the fuel rods are control rods made of neutron-absorbing materials like boron and/or cadmiumneutrons are needed to sustain the chain reaction
• The rods are placed in a material to slow down the ejected neutrons, called a moderatorallows chain reaction to occur below critical mass
Pressurized Light Water Reactor
61
• Design used in United States (GE, Westinghouse) can be recognized by its containment dome of concrete Water is both the coolant and moderator Water in core kept under pressure to keep it from boiling
• Fuel is enriched uranium
PLWR
Core
ContainmentBuilding
Turbine
Condenser
ColdWater
Boiler
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PLWR - Core
ColdWater
FuelRods
HotWaterControl
Rods
The control rods are made of neutron absorbing material. This allows the rate of neutron flow through the reactor to be controlled. Because the neutrons are required to continue the chain reaction, the control rods control the rate of nuclear fission
Concerns about Nuclear Power
64
• Core melt-downwater loss from core, heat melts core
Chernobyl and Fukushima Daiichi
• Waste disposalwaste highly radioactive reprocessing, underground storage?Federal High Level Radioactive Waste
Storage Facility at Yucca Mountain, Nevada
• Transporting waste• How do we deal with nuclear power
plants that are no longer safe to operate?Yankee Rowe in Massachusetts
Where Does the Energy fromFission Come from?
• During nuclear fission, some of the mass of the nucleus is converted into energyE = mc2
• Each mole of U–235 that fissions, produces about 1.7 x 1013 J of energya very exothermic chemical reaction produces 106 J
per mole
65
Mass Defect and Binding Energy
• When a nucleus forms, some of the mass of the separate nucleons is converted into energy
• The difference in mass between the separate nucleons and the combined nucleus is called the mass defect
• The energy that is released when the nucleus forms is called the binding energy1 MeV = 1.602 x 10−13 J 1 amu of mass defect = 931.5 MeV the greater the binding energy per nucleon, the more
stable the nucleus is
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Example19.7: Calculate the mass defect and nuclear binding energy per nucleon (in MeV) for C–16, a radioactive isotope of
carbon with a mass of 16.014701 amu
Solve:
Conceptual Plan:
Relationships:
mass C-16 = 16.01470 amu, mass p+ = 1.00783 amu,mass n0 = 1.00866 amu mass defect in amu, binding energy per nucleon in MeV
Given:
Find:
mp+, mn0, mC-16massdefect
binding energy
68
Practice – Calculate the binding energy per nucleon in Fe–56 (mass 55.93494 amu)
Solve:
Conceptual Plan:
Relationships:
mass Fe-56 = 55.93494 amu, mass p+ = 1.00783 amu,mass n0 = 1.00866 amu binding energy per nucleon in MeV
Given:
Find:
mp+, mn0, mFe-56massdefect
binding energy
69
Nuclear Fusion
• Fusion is the combining of light nuclei to make a heavier, more stable nuclide
• The Sun uses the fusion of hydrogen isotopes to make helium as a power source
• Requires high input of energy to initiate the processto overcome repulsion of positive nuclei
• Produces 10x more energy per gram than fission• No radioactive byproducts• Unfortunately, the only currently working application
is the H-bomb
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Tokamak Fusion Reactor
Making New Elements: Artificial Transmutation
72
• High energy particles can be smashed into target nuclei, resulting in the production of new nuclei
• The particles may be radiation from another radionuclide, or charged particles that are accelerated Rutherford made O–17 by bombarding N–14
with alpha rays from radium
Cf–244 is made by bombarding U–238 with C–12 in a particle accelerator
Cf
73
Artificial Transmutation
• Bombardment of one nucleus with another causing new atoms to be madecan also bombard with neutrons
• Reaction done in a linear particle accelerator or in a cyclotron
Tc-97 is made by bombarding Mo-96 with deuterium, releasing a neutron
74
Linear Accelerator
target
- + - + - + - + - + - + - + - + - + - + - + -
source
+
+ - + - + - + - + - + - + - + - + - + - + - +
+ +
Cyclotron
source
target
75
Predict the other daughter nuclide and write a nuclear equation for each of the following
76
bombarding Ni–60 with a proton to make Co–57
bombarding N–14 with a neutron to make C–12
bombarding Cf–250 with B–11 producing 4 neutrons
77
Predict the other daughter nuclide and write a nuclear equation for each of the following
bombarding Ni–60 with a proton to make Co–57
bombarding N–14 with a neutron to make C–12
bombarding Cf–250 with B–11 producing 4 neutrons
Biological Effects of Radiation
• Radiation has high energy, enough to knock electrons from molecules and break bonds ionizing radiation
• When this energy is transferred to cells, it can damage biological molecules and cause the malfunction of the cell
• High levels of radiation over a short period of time kill large numbers of cells from a nuclear blast or exposed reactor core
• Causes weakened immune system and lower ability to absorb nutrients from foodmay result in death, usually from infection
78
Chronic Effects• Low doses of radiation over a period of time
show an increased risk for the development of cancerradiation damages DNA that may not get repaired
properly
• Low doses over time may damage reproductive organs, which may lead to sterilization
• Damage to reproductive cells may lead to genetic defects in offspring
79
Measuring Radiation Exposure• The curie (Ci) is an exposure of 3.7 x 1010 events/second
no matter the kind of radiation
• The gray (Gy) measures the amount of energy absorbed by body tissue from radiation1 Gy = 1 J/kg body tissue
• The rad also measures the amount of energy absorbed by body tissue from radiation1 rad = 0.01 Gy
• A correction factor is used to account for a number of factors that affect the result of the exposure – this biological effectiveness factor is the RBE, and the result is the dose in rems rads x RBE = rems rem = roentgen equivalent man
80
Factors that Determine theBiological Effects of Radiation
1. The more energy the radiation has, the larger its effect can be
2. The better the ionizing radiation penetrates human tissue, the deeper effect it can have Gamma >> Beta > Alpha
3. The more ionizing the radiation, the larger the effect of the radiation Alpha > Beta > Gamma
4. The radioactive half-life of the radionuclide5. The biological half-life of the element6. The physical state of the radioactive material
81
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Biological Effects of Radiation
• The amount of danger to humans of radiation is measured in the unit rems
Dose (rems) Probable Outcome
20-100decreased white blood cell count; possible increased cancer risk
100-400radiation sickness; increased cancer risk
500+ death
83
Medical Uses of Radioisotopes, Diagnosis
84
• Radiotracersuse radioisotope with a short half-lifeuse radioisotope that is low ionizing
beta or gammacertain organs absorb most or all of a particular
elementyou can measure the amount absorbed by using
tagged isotopes of the element and a Geiger countertagged = radioisotope that can then be detected
and measured
85
Bone Scans
86
Medical Uses of Radioisotopes,Diagnosis
87
• PET scanpositron emission tomographyF–18 tagged glucose
F–18 is a positron emitterbrain scan and function
Medical Uses of Radioisotopes,Treatment – Radiotherapy
88
• Cancer treatmentcancer cells more sensitive to radiation than healthy
cells – use radiation to kill cancer cells without doing significant damage
brachytherapyplace radioisotope directly at site of cancer
teletherapyuse gamma radiation from Co–60 outside to penetrate inside IMRT
radiopharmaceutical therapyuse radioisotopes that concentrate in one area of the body
Gamma Ray Treatment
89
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Nonmedical Uses of Radioactive Isotopes
• Smoke detectorsAm–241smoke blocks ionized air, breaks
circuit
• Insect controlsterilize males
• Food preservation• Radioactive tracers
follow progress of a “tagged” atom in a reaction
• Chemical analysisneutron activation analysis
91
Nonmedical Uses of Radioactive Isotopes
• Authenticating art objectsmany older pigments and ceramics were made
from minerals with small amounts of radioisotopes
• Crime scene investigation
• Measure thickness or condition of industrial materialscorrosion track flow through processgauges in high temp processes weld defects in pipelines road thickness
92
Nonmedical Uses of Radioactive Isotopes
• Agribusinessdevelop disease-resistant crops trace fertilizer use
• Treat computer disks to enhance data integrity
• Nonstick pan coatings initiates polymerization
• Photocopiers to help keep paper from jamming
• Sterilize cosmetics, hair products and contact lens solutions and other personal hygiene products
93
94
Nuclear Medicine
• Changes in the structure of the nucleus are used in many ways in medicine
• Nuclear radiation can be used to visualize or test structures in your body to see if they are operating properlye.g. labeling atoms so their intake and output can
be monitored
• Nuclear radiation can also be used to treat diseases because the radiation is ionizing, allowing it to attack unhealthy tissue
95
