Radiation – Section 2

What is Radiation

What is Radiation

• What is radiation?• Do you have detectors in your 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• For example Carbon has both stable and unstable

nuclides,

• C-12 – Stable

• C-13 – Stable

• C-14 – Unstable

What is Radiation

• Neutrons are the “binding force” of an atom

• The greater number of protons, the more and more neutrons that are required to hold the atom together… the # of 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

• Radionuclides undergo a process referred to as decay (also known as transformation or transition)

• During decay, a radionuclide changes its ratio of protons and neutrons to a more stable combination – it becomes a different nuclide

• In the process some of it’s mass is converted to energy and is carried off by the radiation

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 ~ 83 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

PZ

ADZ-2

A-4+ He

Regions of the Periodic Table

Parent Radionuclide

Alpha Decay

Decay Product

Alpha Particle

Alpha Decay

What is Radiation

• Beta – Beta particles are made up of electrons “born” in the nucleus

• They 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

What is Radiation

• Every time a positron is produced, two 511 keV (kiloelectronvolt) photons will also be produced.

• When the positron has given up all, or almost all, of its kinetic energy, it will combine with an electron

• The electron and positron annihilate each other – their mass is completely converted into energy

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 (β+)

Electron (e-)- an innocent bystander -

Positron Decay

Positron has given up all its kinetic energy.

Positron (β+)

Electron (e-)- an innocent bystander -

Positron Decay

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

Positron (β+)

Electron (e-)

Positron Decay

Positron and electron annihilate each other.

511 keV photon

511 keV photon

What is Radiation

• Sometimes when a nucleus will absorb an orbiting electron

• This is known as electron capture

• A proton will be converted to a neutron without the release of a positron

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

• This is mainly due to its extremely low mass

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

• The gamma is actually emitted from the product of the decay, but is attributed to the parent nuclide

Parent Radionuclide

Gamma Ray Emission

Decay Product (Excited)

Alpha Particle

Gamma Ray Emission

Decay Product

Alpha Particle

Gamma Ray

Gamma Ray Emission

What is Radiation

• Only a specific number of electrons is allowed in each shell (energy level).

• The number of electrons in the various shells determines the chemical properties of the atom.

• Electrons (like all particles) “want” to occupy the lowest possible energy level.

• When an electron moves (undergoes a transition) to a lower energy level, it must release energy.

What is Radiation

• When an electron fills a vacancy in an inner shell (moves to a lower energy level), this energy might take the form of an x-ray.

• X-rays (and gamma rays) have a high enough energy to ionize atoms (remove electrons from atoms) and are therefore considered a type of ionizing radiation.

X-Ray Emitting Atom

Nucleus

X-ray

e-

e-

e-

e-

e-e-

What is Radiation

• Energy can be described as the ability to do work.

• Two kinds of energy:• potential energy• Kinetic energy

• Kinetic energy is the energy of motion (1/2mv2)

• Basic unit: joule (J)• Special unit: electron volt (eV)

1 eV = 1.6 x 10-19 J

What is Radiation

• Gamma, and X-rays are measured in KeV = 103 eV

• Particulate Radiation is measured in MeV = 106 eV

Units• Roentgen (R)

• The roentgen is a unit used to measure a quantity called exposure. This can only be used to describe an amount of gamma and X-rays, and only in air. One roentgen is equal to depositing in dry air enough energy to cause 2.58E-4 coulombs per kg. It is a measure of the ionizations of the molecules in a mass of air. The main advantage of this unit is that it is easy to measure directly, but it is limited because it is only for deposition in air, and only for gamma and x rays.

• Rad (radiation absorbed dose)

• The rad is a unit used to measure a quantity called absorbed dose. This relates to the amount of energy actually absorbed in some material, and is used for any type of radiation and any material. One rad is defined as the absorption of 100 ergs per gram of material. The unit rad can be used for any type of radiation, but it does not't describe the biological effects of the different radiations.

• Rem (roentgen equivalent man)

• The rem is a unit used to derive a quantity called equivalent dose. This relates the absorbed dose in human tissue to the effective biological damage of the radiation. Not all radiation has the same biological effect, even for the same amount of absorbed dose. Equivalent dose is often expressed in terms of thousandths of a rem, or mrem. To determine equivalent dose (rem), you multiply absorbed dose (rad) by a quality factor (Q) that is unique to the type of incident radiation.

• Curie (Ci)

• The curie is a unit used to measure a radioactivity. One curie is that quantity of a radioactive material that will have 37,000,000,000 transformations in one second. Often radioactivity is expressed in smaller units like: thousandths (mCi), one millionths (uCi) or even billionths (nCi) of a curie. The relationship between becquerels and curies is: 3.7 x 1010 Bq in one curie.

• Gray (Gy)

• The gray is a unit used to measure a quantity called absorbed dose. This relates to the amount of energy actually absorbed in some material, and is used for any type of radiation and any material. One gray is equal to one joule of energy deposited in one kg of a material. The unit gray can be used for any type of radiation, but it does not't describe the biological effects of the different radiations. Absorbed dose is often expressed in terms of hundredths of a gray, or centi-grays. One gray is equivalent to 100 rads.

• Sievert (Sv)

• The sievert is a unit used to derive a quantity called equivalent dose. This relates the absorbed dose in human tissue to the effective biological damage of the radiation. Not all radiation has the same biological effect, even for the same amount of absorbed dose. Equivalent dose is often expressed in terms of millionths of a sievert, or micro-sievert. To determine equivalent dose (Sv), you multiply absorbed dose (Gy) by a quality factor (Q) that is unique to the type of incident radiation. One sievert is equivalent to 100 rem.

• Becquerel (Bq)

• The Becquerel is a unit used to measure a radioactivity. One Becquerel is that quantity of a radioactive material that will have 1 transformations in one second. Often radioactivity is expressed in larger units like: thousands (kBq), one millions (MBq) or even billions (GBq) of a becquerels. As a result of having one Becquerel being equal to one transformation per second, there are 3.7 x 1010 Bq in one curie.