Radiation protection

Question 1

why do we need protection?

Answer 1

harmful effects of x-rays were recognised by radiation pioneers, there was a connection found involving biological damage

Question 2

what are the tow types of radiation?

Answer 2

PARTICULATE- high LET, alpha, beta, fast neurons, more destructive.
ELECTROMAGNETIC- low LET, x-ray, gamma

Question 3

Mechanisms of damage

Answer 3

DIRECT ACTION- on the DNA of the material in the nucleus, breaks may occur in the strands
INDIRECT ACTION- radiolysis of water, ionisation of water liberates an electron, producing a free radical that is highly reactive and readily recombines, some cause toxic compounds that may cause cellular damage

Question 4

Nature of damage

Answer 4

• damage is not inevitable
• cells may be unaffected or survive in a modified form
• modification can result in unlimited proliferation, i.e. malignancy

Question 5

radiation effects on cell reproduction

Answer 5

NON-LETHAL DAMAGE- lesions in DNA do not prevent proliferation, heritable mutation, increases sensitivity of future cells
SUB-LETHAL DAMAGE- survival of normal reproductive capacity after recovery time, cellular enzymes locate and eliminate lesions in the DNA
POTENTIALLY LETHAL DAMAGE- survival of normal reproductive capacity provided cells are resting at time of exposure

Question 6

Gray (Gy)

Answer 6

measure of absorbed dose, energy per unit mass of a material

Question 7

sievert (Sv)

Answer 7

measure of efffective dose.
absorbed dose X radiation weighting factor X tissue weighting factor
measure of risk

Question 8

somatic effects

Answer 8

effects on an individual that become apparent within the lifetime of that person

Question 9

genetic effects

Answer 9

effects that are only evident in future generations of the person that has been exposed

Question 10

deterministic effects

Answer 10

• result of cell killing
• severity of damage depends of number of cells lost
• organs renew cells so there is a threshold level for damage

Question 11

stochastic effects

Answer 11

• result of cell alteration
• only a single cell needs to be modified, can result in unlimited proliferation (malignancy)
• no threshold, probability depends on dose

Question 12

radio responsiveness of tissue

Answer 12

RAPID RENEWAL SYSTEM- frequent mitosis, e.g. epidermis. early responding tissue
SLOW RENEWAL SYSTEM- few mitotic cells, e.g. connective tissue. late responding tissue
NON-RENEWAL SYSTEM- no mitosis, e.g. CNS. late responding tissue

Question 13

radio sensitivity of cells at phases in cell cycle

Answer 13

most sensitive during mitosis

most resistant during late s phase

Question 14

what is radio sensitivity of cells in determined by?

Answer 14

• capacity to repair sub-lethal damage
• phase in cell cycle at the time of irradiation
• oxygenation
• type of radiation

Question 15

exposure

Answer 15

measure of the photon flux (flow of photons) to which the point of interest (air) is subjected in a given time. measure of the amount of ionisation produced in a unit mass of air in standard conditions (C.kg-1)

Question 16

radiation exposure measured in air

Answer 16

• ionisation is independent of beam energy
• energy absorbed by human tissue is proportional to the exposure measured in air
• this allows does to be calculated from knowledge of air exposure
• an ionisation chamber is used to measure the charge from the number of ions created within a gas resulting from radiation exposure
• the accumulated charge on the electrodes in the radiation chamber is proportional to exposure

Question 17

geiger-muller counter

Answer 17

• filled with inert gas (helium or neon at low pressure)
• a high voltage is applied
• detects ionisations
• displays count rate (counts per second)
• does not determine energy or type of radiation

Question 18

film badges

Answer 18

• worn at waist height for general monitoring
• finger monitors used for work with live sources
• lithium fluoride is often used
• thermo luminescent properties in result to ionising radiation

Question 19

aims of protection

Answer 19

minimise risk to public, staff and patients

Question 20

three basic principles

Answer 20

SHIELDING- behind shielding from source= less radiation received
TIME
DISTANCE

Question 21

half value layer (HVL)

Answer 21

thickness of a specified material which reduces the intensity of radiation entering the material by half

Question 22

tenth value layer (TVL)

Answer 22

thickness of a specified material that is required to reduce the intensity of the beam to a 10th of its initial value

Question 23

key principles

Answer 23

JUSTIFICATION- no practice should be adopted unless it has a net benefit
LIMITATION- doses to individuals shall not exceed the limits recommended by the commission (ICRP)
OPTIMISATION- alarp