Radiation Safety Course

Heath de la GirodayDispensing Chemist

Radiation Safety Officer

Radiation and Radioactivity

Developed and Produced by:

Radiation Safety Institute of Canada

Course ObjectivesTo provide you with an introduction to UNBC’s Radiation Safety Program and to understand:

1. Radioactivity and Radiation2. Biological Effects of Radiation3. Radiation Safety Regulations & Requirements4. Radiation Protection5. Radiation Monitoring

The First 3 sections will be reviewed by the students before the training class begins

In This Session…• Structure of matter• Radiation• Ionizing and non-ionizing radiation• Radioactive decay• Common types of ionizing radiation

– Alpha– Beta– Gamma

• Activity and half-life

The AtomThe atom is composed of:

Nucleusprotons,

neutrons,

and

electrons.

The Atom

ParticleMass

(amu)Charge

Proton 1 +1

Electron 1/1836 -1

Neutron 1 0

NomenclatureAtoms are often written with the notation:

SymbolAZ

Atomic Number

Mass Number

Chemical symbol(H for Hydrogen, C for Carbon, Pb for Lead, etc.)

Another common notation is: Symbol-A

RadioactivityMost atoms in nature are stable.

If an atom is not stable,it is said to be unstable.

Stable implies that the forces acting on the nucleus of the atom are strong enough to hold it together indefinitely.

Radioactivity

Unstable atoms want to become stable!

While becoming stable, unstable atoms emit radiation. This process is known as radioactive decay.

In an unstable atom, the nuclear forces are not strong enough to hold the nucleus of the atom together.

RadioisotopesAtoms that are unstable are called radioactive.

Radioactive atoms can emit various types of radiation with different amounts of energy.

Radioactive atom, also known as:

radioisotope radionuclideor

Isotopes of Hydrogen

Sources of Radiation

Radioactive atoms Man-made devices

Where does radiation come from?

Man-made1%

Medicinal18%

Radon62%

Cosmic6%

Terrestrial7%

Internal6%

Radiation Sources

Radiation and Energy

• Radiation can be interpreted as a form of energy.

• Radiation will interact differently with matter depending upon how much energy it has.

Interaction with MatterWhen radiation strikes matter, it interacts with the atoms of the matter.

RadiationAtom

Electron

Radiation with enough energy can knock electrons out of orbit from the atoms it strikes.

Ionizing Radiation

Ion PairNeutral Atom

Electron

The process of creating ions is called ionization.

Radiation which can cause ionization is known as ionizing radiation.

Types of Ionizing Radiation

Ionizing

Radiation

Alpha

Beta

Gamma

Proton Neutron

Non-Ionizing RadiationRadiation which does not have enough energy to ionize atoms is called non-ionizing radiation.

Visible Light

Microwaves

Radio Waves

Infrared Light

The Electromagnetic Spectrum

Radiation

• Non-ionizing radiation– thermal– radio– microwave– infrared– visible light– ultraviolet

• Ionizing radiation– alpha particles– beta particles– gamma photons– x-rays– neutrons

Radioactive Decay

• The process of radioactive decay may continue until the resulting atom is stable

• Some decay series, such as that of uranium, are quite long

• While others, such as that of iodine, are short

Uranium Decay Series

In total,14 radioactive decays occur before the original radionuclide transforms into the stable isotope of lead.

U-238

Th-234Pa-234mU-234

Th-230

Ra-226

Rn-222

Po-218

Pb-214Bi-214Po-214

Pb-210Bi-210Po-210

Pb-206

4.5 billion years

3.8 days

3 minutes

Stable!

Iodine Decay

• Iodine-131 decays to xenon-131 which is a stable nuclide

e)stable(XeI 01

13154

13153

Alpha RadiationNucleus of a helium

atom (4He)Composed of two protons

and two neutrons

Carries two units of positive charge (+2)

Emitted from the nuclei of radioactive atoms

Alpha Particles ()

• Highly energetic• 2 neutrons, 2 protons• Double charge• Limited penetrating

ability• Low external hazard• High internal hazard

42

22286

22688

42

42

RnRa

YX AZ

AZ

Alpha Ionization• Alpha particles are highly ionizing.

• They can easily strip loosely bound electrons from atoms.

• Because of its size, the alpha particle does not travel far in matter:– Approximately 7 cm of air– Stopped by a piece of paper– Will not penetrate the dead outer layer of your skin

Beta Particles (-) • Electron emitted from the

nucleus• Faster than • Smaller size• Single charge• External hazard to skin

and eyes– except H-3

• Internal hazard

SP

YX AZ

AZ

3216

3215

1

Beta Radiation Penetration

• Maximum energy values for beta particles vary from 18 keV for 3H to 4.81 MeV for 38Cl

• Beta particles are less ionizing than alpha particles and can travel farther in matter:– Approximately 200 cm in air– They can penetrate the skin– Approximately 0.2 cm in tissue

• A thin layer of plastic is an effective shield.

Typical Beta Emitters

P-32 I-131 Na-22

C-14 H-3 Sr-90

Examples of Beta DecayPhosphorus-32

Sulfur-32

Beta particle (electron)

Beta Radiation• When beta particles pass through

matter, x-rays can be produced.

X-ray machine

• The higher the atomic number, the more bremsstrahlung will be produced.

– This is called bremsstrahlung, meaning “braking radiation”

Negative Beta Decay

• Like alpha decay, negative beta decay also results in the creation of a new atom which may itself be radioactive.

• For example, iodine undergoes beta decay and transforms into xenon

e)stable(XeI 01

13154

13153

Positive Beta Decay

• Another example of beta decay is positron decay, which also results in the creation of a new atom

eNeNa 01

2210

2211

Gamma Photons ()

• Electromagnetic radiation• Originate inside nucleus• No charge or mass• Travel at the speed of light• External hazard to whole body• Internal hazard

Gamma Radiation

• Gamma radiation is not made up of physical particles like alpha or beta radiation.

• Gamma radiation is made up of photons.

– Photons are packets of energy with no mass.

Gamma Radiation

• In other words, gamma radiation is electromagnetic radiation just like ordinary light.

• The energy of gamma radiation is much greater than that of ordinary light.

Electromagnetic Spectrum

Courtesy NASA/JPL-Caltech

Gamma Emission

• Gamma rays are emitted from the nuclei of radioactive atoms.– Unlike x-rays which are produced through

electron interactions.

• The emission of a gamma ray is always preceded by either a beta decay or an alpha decay.

X-rays are emitted when high speed electrons are slowed down or change direction as a result of interactions with atoms in a target material.

X-Rays

X-ray

Gamma Rays and X-Rays

• Both gamma rays and x-rays are ionising radiation.

• Gamma rays and x-rays do not have a range. – They can theoretically travel forever.

• However, as gamma rays and x-rays pass through matter, their intensity is reduced.

Penetrating Power

Paper Aluminium Lead

Radiation Units

• 1 becquerel (Bq) = 1 dps = 60 dpm– kBq, MBq, GBq, etc.

• 1 curie (Ci) = 3.7 1010 Bq– mCi, Ci, nCi, etc.

• Knowledge of both unit systems is necessary– 1 Ci = 37 GBq 1 Ci = 37 kBq– 1 mCi = 37 MBq 1 nCi = 37 Bq

Activity

• The rate of radioactive decay is referred to as the activity.– The number of decays per unit of time.

• The SI unit of activity is the becquerel (Bq).– One becquerel is one decay per second.

• The historic unit for activity is the curie (Ci).1 Ci = 3.7 × 1010 Bq

Activity

• Activity of 1 mg of U-238 is 10 Bq

• Activity of 1 mg of Am-241 is 1x108 Bq

• The drastic difference in activity between uranium-238 and americium-241 is related to a unique property of all radionuclides called the half-life

Radiation Quantities

Exposure

Absorbed Dose

Equivalent Dose

Air Matter (Tissue)

Exposure• Exposure is a means of measuring intensity of

ionizing radiation IN AIR• Coulomb/kilogram (C/kg)

– Amount of radiation-induced ionizations in a unit mass - not generally used

• Roentgen (R)– Quantity of radiation that produces 1 statcoulomb of

charge of either sign per cm3 of air at 0C and 760 mm Hg - this is not important

– It is found that 1 R = 0.00877 J/kg 0.01 J/kg – Most radiation meters at UNBC read in mR

Activity vs. Exposure

• Activity: measured in Bq relates to nuclear disintegrations per second while Exposure: measured in Sievert relates quantitatively how much damage (biological effectiveness) is done to tissue, or air

• The amount of energy deposited by radiation per unit mass IN TISSUE MATTER

• Gray (Gy)– 1 Gy = 1 J/kg

• Rad (radiation absorbed dose)– 1 rad = 0.01 J/kg

• Therefore:– 1 Gy = 100 rad

Absorbed Dose

• As different types of radiation produce different amounts of damage

• Equivalent dose is the measure of the biological effect of radiation weighted for the type of radiation

• H = absorbed dose (Gy) weighting factor• Weighting factors (wR)

– Beta particles wR = 1– Gamma photons wR = 1– Alpha particles wR = 20

Equivalent Dose

Radiation Quantities

2. Exposure

3. Absorbed Dose

4.Equivalent Dose

Air Matter (Tissue)

It is important to know the difference between the four term!

1. Activity

Half-Life

• The half-life of a radionuclide is the time required for it to lose 50% of its activity by radioactive decay.

• Each radionuclide has its own unique half-life, regardless of the quantity or form:– Solid

– Liquid

– Gas

– Element or compound

Half-Life

00.10.20.30.40.50.60.70.80.9

1

0 5 10 15

Elapsed Time (days)

Rela

tive A

ctiv

ity

Rn-222Half-life = 3.82 days

3.82

Half-Life

• The half-life of a radioisotope is an unalterable property of the radioisotope.

• Half-lives range from microseconds to billions of years.

– Uranium-238 4.5 x 109 years

– Cesium-137 30.07 years

– Radon-222 3.8 days

– Polonium-212 3.04 x 10-7 seconds

Half-Life Example• Assume we have 1000 Bq of P-32.

– P-32 has a half-life of 14.3 days.

# of half-lives elapsed Activity remaining

One half-life (14.3 days)

500 Bq

Two half-lives (28.6 days)

250 Bq

Three half-lives (42.9 days)

125 Bq

Half-Life

• A good rule of thumb to remember is that after 7 half-lives the activity decreases to about 1% of the original value.

• After 10 half-lives the activity reduces to about 0.1% of the original value.

Half-Life

• Activity and half-life are related mathematically by the following equation:

• A is the activity remaining after n half-lives– A0 is the original activity present

n0 2

1

A

A

BIOLOGICAL EFFECTS

• Health Effects of Exposure to Radiation

In This Session…

• Radiation dose

• Indirect effects of radiation

Direct effects of radiation– Hereditary effects– Somatic effects

• Stochastic effects• Deterministic effects

Radiation Dose

• Radiation dose, in the simplest terms, can be thought of as the amount of radiation an individual is exposed to either from:

– Work activities with radioactive materials

– Medical tests such as from a diagnostic x-ray

– Background radiation

Radiation Dose Measurement

• The measurement of an individual’s radiation dose is very complicated and depends on many factors:– Type of radiation– Type of exposure

• External• Internal

– Duration of exposure

Radiation Dose

• When radiation passes through matter, it interacts with molecules and atoms giving up some or all of its energy

• The amount of energy transferred to the matter is referred to as the radiation dose

Radiation Dose

• In living tissue, this energy transfer or radiation dose can result in damage to molecules and cells

• In radiation safety, there are three categories of radiation dose:– Absorbed dose

– Equivalent dose

– Effective dose

Radiation Quantities

Exposure

Absorbed Dose

Equivalent Dose

Effective Dose

Air Matter (Tissue)

Review- Absorbed Dose

• Absorbed dose is a measure of the amount of radiation energy transferred to matter per unit mass

• The unit of absorbed dose is the gray (Gy)

1 Gy = 1 J/kg

– Where J (joule) is a unit of energy

Review- Equivalent Dose• The equivalent dose is simply the absorbed dose

multiplied by a radiation weighting factor• The radiation weighting factor helps to account for the

different levels of biological damage caused by different types of radiation

• Different types of radiation (alpha, beta, neutrons, gamma, x-rays) will, by their nature, cause different amounts of damage in living tissue

• The unit of equivalent dose is the millisievert (mSv)

Radiation Weighting Factors

Radiation Energy wR

Gamma / x-ray All 1

Beta All 1

Alpha particles (internal) All 20

Radiation Dose to Tissues

• We now know that different types of radiation cause different levels of damage in living tissue

• In addition, some tissues in the body are more sensitive to radiation than others

– Reproductive organs are more sensitive to radiation than the skin or the lungs

Radiation Dose to Tissues

• The equivalent dose does not account for the varying sensitivities to radiation exposure of different organs or tissues in the body

• There is a need for a common scale with which to measure the overall risk to a person’s health, regardless of which tissue or organ is exposed

• This takes us to the effective dose

Effective Dose

• The effective dose is the equivalent dose multiplied by a tissue weighting factor

• The tissue weighting factor helps to account for the varying sensitivities to radiation exposure of the different tissues and organs

• The unit of effective dose is the millisievert (mSv)

Effective Dose

• Effective dose accounts for the type of radiation and the tissue or organ irradiated

• 1 mSv of effective dose is just 1 mSv, regardless of whether the dose was delivered to the lungs, thyroid, bone marrow, or any other tissue.– Unfortunately, mSv is the unit equivalent dose as

well as effective dose though they are not equal

Equivalent v. Effective Doses

• Equivalent dose is the unit used to assess doses to individual tissues or extremities– Tissues are treated separately– There are equivalent dose limits for skin, hands and

feet

• Effective dose is the unit used to assess doses on the scale of the whole body– Tissue doses are weighted to indicate effect on the

body as a whole

Molecular Effects of Irradiation

• In living systems, biological damage can occur as a result radiation-induced damage to molecules and cells

• Radiation may cause damage to molecules or cells either directly or indirectly

• About 60% of human body weight is water.

• Water is a simple molecule consisting of one oxygen (O) and two hydrogen (H) atoms.

• Its chemical representation is: H2O.

H

O

H

Indirect Damage

• Ionizing radiation can break apart water molecules to create free radicals.

• H2O H· + OH·

• Both hydrogen and oxygen normally exist as H2 and O2 molecules, respectively.

• Free radicals are chemically reactive atoms or molecules

Indirect Damage

H2O

Indirect Damage• Indirect damage involves the effects of

reactive free radicals created by the interaction of radiation with water (H2O).

H2O

Ionization

Toxic H2O2

Indirect Damage

• The fractured water molecule components, H and OH, can undergo a variety of reactions:

• H· + OH· H2O (Water)

– H· + H· H2 (Hydrogen gas)

– OH· + OH· H2O2 (Hydrogen peroxide)

– Hydrogen peroxide is a chemical poison. – Its effects resemble radiation sickness (nausea,

vomiting, diarrhoea, malaise).

H2O2

Direct Damage• When radiation interacts directly with vital

biological molecules such as DNA (deoxyribonucleic acid), RNA (ribonucleic acid), proteins and enzymes, damage to these molecules can occur through ionization interactions and the absorption of energy

• These ionization and excitation interactions can literally break chemical bonds resulting in impaired molecular function

Radiation Effect Categories

– Hereditary (genetic) effects

– Somatic (body) effects

• The effects of exposure to radiation can be divided into two categories:

Hereditary Effects

• Hereditary effects are those which do not become apparent until future generations are born

• Possible result of radiation induced damage to the DNA molecule in the germ cells (sperm, ova).

Hereditary Effects in Humans

• Effects from the nuclear bomb explosions in Japan:– Hereditary effects such as leukemia and

developmental delays have only been seen in those children who were heavily irradiated while still in their mother’s womb

– Children conceived after the explosion have shown no change in the natural mutation rate

• The findings are not statistically sound

Somatic Effects

• Somatic effects are those which are experienced directly by the people exposed to the radiation

• There are two types of somatic effects:– Stochastic effects– Deterministic effects

Stochastic Effects

• All we can say is that radiation exposure increases the likelihood of developing a disease such as cancer

• The greater the exposure, the greater the likelihood

• We can never be certain that an effect will occur

DNA Damage

• When radiation interacts with living tissue, molecular bonds can be broken and cell function altered

• If a DNA molecule is damaged:– The body may be able repair the DNA,– The cell may die,

or– The DNA is not repaired properly resulting in a

mutated cell with altered function

Mutation Effects

• A radiation dose has a certain probability of causing a mutation in a cell.

• A mutation might bring about cell destruction.• A mutation could affect cell behaviour and increase

the rate of cell divisions.– The new cells will have the mutation causing them

to also divide before reaching their mature state.– They will provide no beneficial function to the

body.

Tumors

• These cells form a tissue called a tumour. – If the cells do not invade surrounding tissues,

the tumour is benign.– If the tumour invades neighbouring tissues it

is malignant.

• A malignant tumour is cancer which may or may not be fatal.

Radiation-Induced Cancers• Early radiation scientists

– Many died from skin, bone, and blood cancers.• Radium watch dial painters

– Many died of bone cancer 8 to 40 years later.• UK X-ray patients

– 6,500 patients were treated with 3 Gy x-rays. – 30 developed leukemia (7 expected without x-rays).

• Japanese bomb survivors (80,000 people)– 350 cancer deaths, double the expected figure.

Latency Period

• There is a delay between exposure to the radiation and the onset of cancer.

• This delay is known as the latency period. – For leukemia, it is about 8 years.– For other cancers, it can be much longer.

Risk: Cancer from Radiation• The risk of developing a fatal cancer as a result of

exposure to radiation is thought to be approximately 4% per 1000 mSv

• Consider a person who worked for 50 years and received 20 mSv per year– This person’s total lifetime radiation dose would be

1000 mSv– This person could have an extra 4% chance of

developing a fatal cancer

Risk: Cancer in General

• Note that 25% of all people develop a fatal cancer in their life

• So, this person’s risk of developing cancer becomes 29%, instead of 25%

• No profession is risk free

Deterministic Effects

• A deterministic effect is one which will certainly result from exposure

• There will be a minimum exposure (threshold) above which the effect will occur

• The severity of the effect will depend on the exposure– Example: cataract formation, radiation sickness

Chronic Exposure

• Exposure to low doses of radiation over months or years

• Deterministic effects– Cataracts– Nonspecific life shortening

• Stochastic effects– Cancer– Genetic effects

Acute Exposure

• Exposure to a high dose delivered within seconds, minutes or days

• Possible deterministic effects– Blood changes– Nausea– Diarrhea– Hair-loss– Malaise– Death

Acute EffectsAcute Dose (mSv) Probable Effects

100 None detectable. 250 Only detectable by

chromosome analysis. 500 Minor changes to blood cells.

1000 Possible radiation sickness and skin reddening. Very slight chance of death.

Acute EffectsAcute Dose (mSv) Probable Effects

2500 Radiation sickness. Some

risk of death without medical treatment; recovery very likely with treatment.

4500 50% will die without medical treatment; some risk of death with treatment.

10,000 100% will die without medical treatment; high risk of death with treatment.

Acute Exposure

• The rapidly reproducing cells are most affected by acute radiation:– The skin– The blood-forming tissues– The gonads– The digestive system lining (the

gastrointestinal tract or GI tract)

• Acute Effects= deterministic effects– clear relationship between dose and effect

once threshold is crossed

• Delayed Effects= stochastic effects– dose increases probability of an effect,

rather than its magnitude or severity

Biological Effects

Delayed Effects• The increased risk of a fatal cancer due to

exposure to radiation is 0.004% per mSv.• This is in addition to the 25% risk that all people

have of contracting a fatal cancer.• Thus, an exposure of 1 mSv increases a

person’s risk of dying of cancer from 25% to 25.004%.

• Note: The occupational exposure limit at UNBC is 1 mSv.

Biological Effects – Summary

• Although the risk associated with working with radioisotopes and radiation is low, it is not zero.

• Each individual must decide for themselves if they are willing to accept this risk.

• If someone decides to accept this risk, they should practice ALARA– As Low As Reasonably Achievable

• Radiation safety depends primarily on the user.

REGULATIONS

Federal Regulations

• Canadian Nuclear Safety Commission (CNSC)– Nuclear Safety and Control Act

• Radiation Protection Regulations• General Nuclear Safety and Control Regulations• Nuclear Substances and Radiation Devices

Regulations• Packaging and Transport of Nuclear Substances

Regulations

Federal Regulations

• Canadian Nuclear Safety Commission (CNSC)– Issues licenses to users that permit work with

radioactive materials– License conditions– Penalties for violation

CNSC Dose Limits

Type of Dose

Members of the Public

(mSv/y)

Nuclear Energy Workers (mSv/y)

Effective Dose 1 20

Dose to the Lens of an Eye

15 150

Dose to the Skin 50 500 Dose to the Hands

and Feet 50 500

UNBC Radiation Safety Program

• Radiation Safety Policy

• Committee on Radioisotopes and Radiation Safety

• Radiation Safety Officer

• Individual Users

UNBC Radiation Safety Program

• Radiation Safety Policy– Applies to all teaching and research activities– Outlines responsibilities of:

• Committee on Radionuclides and Radiation Safety• Radiation Safety Officer• Deans, Directors and Department Chairs

UNBC Radiation Safety Program

• Committee on Radioisotopes and Radiation Safety– Develop policies and procedures– Provide advice and make recommendations– Issue Internal Radioisotope Permits to faculty

Internal Radioisotope Permits

• Allow specified radioisotopes to be used for particular purposes in certain locations

• Restrictions ensure (in part) compliance with CNSC licenses

• Each faculty member working with radioisotopes or radiation requires an IRP

• Non-compliance may result in IRP being revoked

UNBC Radiation Safety Program

• Radiation Safety Officer– Reports to CRRS and VP Admin & Finance– Reviews IRP applications– Approve radioisotope orders– Maintain documents– Deliver radiation safety training– Conduct inspections

UNBC Dose limit

The occupational exposure limit at UNBC is 1 mSv.

UNBC Radiation Safety Program

• Individual users– Comply with safety policies and procedures– Seek guidance from immediate supervisor– Attend safety training or meetings– Immediately report accidents or hazardous conditions

to immediate supervisor

• Supervisors are also responsible for ensuring that students are adequately supervised and instructed in laboratory safety

UNBC Policy for Pregnant Women

• The UNBC Committee on Radioisotopes and Radiation Safety recommends that the dose to the abdomen of a pregnant woman not exceed that of the general population

• Women are encouraged to disclose their pregnancy to their Department Head, in confidence, as early as possible

• Department Head will notify the worker’s Supervisor and the Radiation Safety Officer

UNBC Policy for Pregnant Women

• The woman’s radiation work will be reviewed to determine if the dose rate can be reduced to near background levels

• If the dose rate cannot be reduced to about background, cessation of the work will likely be recommended

• Lab entry will be denied to any pregnant worker approaching her dose limit

UNBC Policy for Pregnant Women

• A pregnant woman may indicate that she wants to continue with her radiation work by signing a form indicating she is aware of the potential risks but wishes to continue– this form is available from the RSO

• All actions regarding pregnant worker’s will be reviewed by the UNBC Committee on Radioisotopes and Radiation Hazards