Radiation – Section 2

What is Radiation

What is Radiation

• What is radiation?• Do you have detectors in our homes?

• Do you have radiation sources in your homes?

• Radiation is energy that radiates from a source…• i.e. Light, Heat, X-Rays, etc.

• As we can see there are many different types of radiation

What is Radiation

• Why is there radiation?

• In nature there are “stable” and “unstable” nuclei

• Neutrons are the “binding force” of an atom

• The greater number of protons, the more and more neutrons are required to hold the atom together… #’s neutrons in stable atoms is not always the same # of protons

What is Radiation

• Since like charges repel one another, the more protons you have repelling each other in different directions….many more neutrons than protons will be required

• As an atom approaches stability the changes in the nuclei cause radiation, the stability is gained by the ratio of neutrons and protons coming closer to 1/1

What is Radiation

• The physical characteristics of radiations include; mass, charge, point of origin (where it’s found)

• There are two possible points of origin• Nucleus

• Electron Cloud

• Most radiations originating outside the nucleus are not in the scope of this course, these including…visible light, radio, etc.

What is Radiation

• Radiations also can be characterized by their effects on matter

• When atoms are exposed to radiation they are either created into ions or not, therefore we classify radiation as either…• Ionizing

• Non-Ionizing

• In this course we are concerned only with ionizing forms of radioactivity

What is Radiation

• There are two major types of ionizing radiation• Particulate Radiation• Electromagnetic Radiation

• Particulate Radiation is solid matter, consists of particles, therefore has mass or substance

• Electromagnetic Radiation is made up of waves of pure energy, therefore having no mass

What is Radiation

• There are three types of particulate radiation• Alpha

• Beta

• Neutron

• Alpha radiation is made of 2 protons and 2 neutrons, therefore having an atomic mass of 4 (ionized helium nucleus)

• Alpha radiation has a charge of +2 and as it travels through air it “ionizes” atoms

What is Radiation

• Alpha particles are emitted from the nuclei of large atoms ~ 80 protons and up

• The reason large atoms give off “large” particles i.e. alpha particles is because they are very unstable therefore need to give off large amounts of mass

What is Radiation

• Beta – Beta particles are made up of electrons

• They have a mass of 1/2000th AMU and can have either a + or – charge

• Even though positive electrons are not supposed to exist, under some circumstances they can be produced in the nuclei of atoms

• These positive electrons (positrons) are more commonly known as antimatter

What is Radiation

• Beta particles are a result of protons and neutrons changing identity

• When a neutron changes to a proton (neutron conversion) a negative electron is emitted

• When a proton changes to a neutron (positron emission) a positive electron is emitted• Discuss electron capture

What is Radiation

• When the negative electron leaves the nucleus, it travels close to the speed of light

• This is mainly due to its extremely low mass

• However, when the positron leaves the nucleus, being antimatter (+), it immediately runs into a negative electron and there occurs a matter/antimatter annihilation…Example, Na22 gives off a positron and can be measured at 511 KeV

p

p p

nn

p

Parent Radionuclide

Positron Decay

p

p n

nn

p

Decay Product

Positron

Neutrino

Positron Decay

p

p p

nn

p

Decay Product

Positron

Neutrino

Positron Decay

Positron Decay

Positron (+)

Electron (e-)- an innocent bystander -

Positron Decay

Positron has given up all its kinetic energy.

Positron

Electron (e-)- an innocent bystander -

Positron Decay

Because of their opposite charges, the positron and electron are attracted to each other.

Positron

Electron (e-)

Positron Decay

Positron and electron annihilate each other.

511 keV photon

511 keV photon

What is Radiation

• Neutrons are the last type of particulate radiation that we will discuss

• Neutrons have a mass of 1 AMU and ø charge

• They are produced most commonly in nuclear reactors from when atoms fission

What is Radiation

• Now that we have looked at the types of particulate radiation, we will now look at the types of electromagnetic radiation

• Remember electromagnetic radiation is waves of pure energy for example; light, x-rays and all other members of the electromagnetic spectrum

What is Radiation

• Gamma – Gamma rays are electromagnetic rays of pure energy

• They have no mass and no charge

• Gamma rays are produced as a result of the de-excitation of the nucleus of atoms that have given off either an alpha or a beta particle

• Gamma rays are measured in KeV = Kiloelectron Volts

What is Radiation

• X-rays have the same general characteristics as gamma rays… the only difference is where they are emitted from

• We will discuss x-rays later in the course when we look at medical applications of radiation

What is Radiation

• Gamma rays are measured in KeV = Kiloelectron Volts

• Particulate Radiation is measured in MeV = Million Electron Volts

What is Radiation

• When we looked at the atom we learned the term “isotope” we have also seen the difference between stable and unstable atoms… it is important to know that an element can have both stable and unstable isotopes

• Unstable isotopes are all radioactive

What is Radiation

• The term Nuclide refers to any atom where the mass is stated and the atomic number is either stated or inferred, i.e. U238, 92U238

• This is where the chart of the Nuclides comes from, this chart shows all elements AND all the known isotopes of those elements

• We will look at this chart in detail later in the semester