Ionising Radiation

Question 1

What are the natural sources of radiation

Answer 1

Cosmic radiation, animals, rocks, buildings, soil, plants, food, water, people, radon gas

Question 2

What are the artificial sources of radiation

Answer 2

X-ray machines, nuclear power, nuclear missiles, nuclear weapons testing

Question 3

Characteristics of ionising radiation

Answer 3

Penetrating (absorbed and scattered in a medium)

Invisible (to the eye)

Reduces in intensity with half-value layer & inverse square law

Can cause radiation-induced tissue damage/biological effects

Radioactive materials (isotopes) have activity (half-life)

Question 4

Describe the half-value layer (HVL)

Answer 4

Thickness of a substance which will transmit one 1/2 of the intensity of the radiation incident upon it

Question 5

Describe the half-life

Answer 5

Time taken for half of the atoms to decay

Question 6

Inverse square law

Answer 6

I = 1/d2

Question 7

Three practical principles of radiation safety

Answer 7

Time - time spent near the source of radiation

Distance - distance from the source of radiation

Shielding - shielding can be used if source is too intensive

Question 8

Lead (Pb) Equivalent

Answer 8

Thickness of lead which would absorb the same amount of radiation as the given material when exposed to radiation of the same type

Question 9

Lead (Pb) Equivalence shielding

Answer 9

Mobile X-ray procedures
- 0.25mm lead equivalence

Fluoroscopic procedures
- 0.5mm lead equivalence

Question 10

What is radon gas

Answer 10

Formed by radioactive decay of small amounts of uranium naturally occurring in rocks and soil

Question 11

Radioactive foods - Banana dose equivalent

Answer 11

Informal way of comparing ionising radiation to the dose received by eating a single banana

Question 12

Alpha decay

Answer 12

Spontaneous emission of an alpha particle from a nucleus (2 protons & 2 neutrons)

Most strongly ionising and destructive form of ionising radiation

Question 13

Beta decay

Answer 13

Spontaneous emission of a fast-moving particle with the mass of an electron from a nucleus

-ve and +ve beta particles are produced by the decay of either a proton or a neutron

Question 14

Radioactive decay

Answer 14

Process by which an unstable atomic nucleus loses energy by emitting radiation, such as an alpha particle, beta particle or gamma ray

Question 15

Gamma decay

Answer 15

Spontaneous emission of a high energy photon (no mass) from a nucleus

Question 16

How is radiation stopped

Answer 16

Alpha radiation - stopped by a sheet of paper

Beta radiation - stopped by an aluminium plate

Gamma radiation - absorbed as it penetrates a dense material (lead)

Question 17

Radiation-induced tissue damage

Answer 17

Direct action or damage - ionisation of macromolecules (DNA, RNA, proteins, enzymes) = abnormal replication/cell death effects somatic cells or reproductive cells

Indirect action or damage - free radicals produced by ionisation of water (breaking chemical bonds)

Question 18

Compton scatter

Answer 18

Ejected electron goes on to interact with other atoms via ionisation and excitation

Question 19

Linear energy transfer (LET)

Answer 19

Amount of energy transferred per unit length

High - +ve charged particle attracts electrons & ejects them from their atoms

Low - -ve charged particle repels electrons & ejects them from their atoms

Question 20

Biological effects of ionising radiation

Answer 20

Tissue reactions - non-cancer damaging effects that will definitely result from high dose radiation (threshold)

Stochastic effects - cancer and genetic effects that may result or develop (no threshold)

Question 21

Radiation quantities and units

Answer 21

Absorbed dose - energy deposited per unit mass - measured in J/kg-1 or SI unit gray (Gy)

Equivalent dose = absorbed dose x radiation weighting factor - measured in sievert (Sv)

Effective dose = sum of (equivalent dose x tissue weighting factor) - measured in sievert (Sv)