Ionising Radiation Flashcards
What are the natural sources of radiation
Cosmic radiation, animals, rocks, buildings, soil, plants, food, water, people, radon gas
What are the artificial sources of radiation
X-ray machines, nuclear power, nuclear missiles, nuclear weapons testing
Characteristics of ionising radiation
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)
Describe the half-value layer (HVL)
Thickness of a substance which will transmit one 1/2 of the intensity of the radiation incident upon it
Describe the half-life
Time taken for half of the atoms to decay
Inverse square law
I = 1/d2
Three practical principles of radiation safety
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
Lead (Pb) Equivalent
Thickness of lead which would absorb the same amount of radiation as the given material when exposed to radiation of the same type
Lead (Pb) Equivalence shielding
Mobile X-ray procedures
- 0.25mm lead equivalence
Fluoroscopic procedures
- 0.5mm lead equivalence
What is radon gas
Formed by radioactive decay of small amounts of uranium naturally occurring in rocks and soil
Radioactive foods - Banana dose equivalent
Informal way of comparing ionising radiation to the dose received by eating a single banana
Alpha decay
Spontaneous emission of an alpha particle from a nucleus (2 protons & 2 neutrons)
Most strongly ionising and destructive form of ionising radiation
Beta decay
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
Radioactive decay
Process by which an unstable atomic nucleus loses energy by emitting radiation, such as an alpha particle, beta particle or gamma ray
Gamma decay
Spontaneous emission of a high energy photon (no mass) from a nucleus
How is radiation stopped
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)
Radiation-induced tissue damage
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)
Compton scatter
Ejected electron goes on to interact with other atoms via ionisation and excitation
Linear energy transfer (LET)
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
Biological effects of ionising radiation
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)
Radiation quantities and units
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)
