5. Radiation Protection

Question 1

what are the 2 types of personal dosimeters badges and what must be done before the dose can be read

what kind of dose do they measure

Answer 1

thermolumiscent or film types

requires processing to reveal cumulative dose received

Question 2

what are the 4 types of personal dosimeters

Answer 2

film badge

pocket ionizing chambers

thermoluminescent dosimeters

optically simulated luminescence

Question 3

how do film badges work and what change do they undergo when its exposed to radiation

what is it measured with and what can be used to identify energy range

Answer 3

radiation darkens the developed x-ray film
amount of darkening increases with absorbed dose

measured with a densitometer

filters used to identify energy range

Question 4

what is the crystal in thermiluminescent dosimeters

how does it work and what causes it to luminescence

amount of radiation dose is proportional to what

Answer 4

lithium fluoride crystal

traps and stores energy from ionising radiation
will luminescence if heated

measure intensity of light emitted and amount of light is proportional to radiation dose

Question 5

what is the crystal in optically stimulated luminesce dosimeters

how does it work and what causes it to luminescence

amount of radiation dose is proportional to what

Answer 5

aluminum oxide crystal

traps and stores energy from ionising radiation
will luminescence if illuminated

measure intensity of light emitted and amount of light is proportional to radiation dose

Question 6

what is the difference between what causes the luminescence for TLD and OSL dosimeters

Answer 6

TLD will luminescence if heated

OSL will luminescence if illuminated

Question 7

how does the pocket ionisation chamber work as a dosimeter

what is the absorbed dose proportional to

is processing required

can it be reused and reset

Answer 7

radiation incident on chamber produces ionisation

voltage difference is produced as gas is ionised
voltage is directly proportional to the absorbed dose

dose is read directly from dosimeter, no processing required

yes can be reset and reused

Question 8

what 2 types of radiation does a pocket ionisation chamber dosimeter measure

Answer 8

gamma

x-ray

Question 9

what 3 types of radiation does a film badge dosimeter measure

Answer 9

beta
gamma
x-ray

Question 10

what 3 types of radiation does a TLD measure

Answer 10

beta
gamma
x-ray

Question 11

what 3 types of radiation does a OSLmeasure

Answer 11

beta
gamma
x-ray

Question 12

what are 2 advantages to using a pocket ionisation chamber dosimeter

Answer 12

immediate reading

reasonably accurate

Question 13

what are 4 advantages to using a film badge chamber dosimeter

Answer 13

permanent legal record
most common
cheap
can re-read

Question 14

what are 2 advantages to using a TLD dosimeter

Answer 14

more accurate than film

durable, resistant to humidity

Question 15

what are 3 advantages to using a OSL dosimeter

Answer 15

more accurate than film

durable resistant to heat and humidity

can be re-read

Question 16

what are 5 disadvantages to using a pocket ionisation chamber dosimeter

Answer 16

no permanent legal record

reading can be lost

must be read each day

false readout if jarred/dropped

expensive

Question 17

what are 3 disadvantages to using a film badge dosimeter

Answer 17

must be measured

affected by heat and humidity

accuracy limited

Question 18

what are 4 disadvantages to using a TLD dosimeter

Answer 18

no permanent/legal record

must be measured

cant reread

more expensive than film

Question 19

what are 3 disadvantages to using a OSL dosimeter

Answer 19

no permanent/legal record

must be measured

more expensive than film

Question 20

the effective dose must be well below what limits over how long

Answer 20

well below 20mSv per year averaged over 5 consecutive years or a max of 50mSv in any single year

Question 21

what kind of dose is especially a problem and why

Answer 21

cumulative dose is a problem as the more radiation exposed to overtime = more mutations likely to occur

Question 22

what are the 3 components to ALARA

Answer 22

shielding
distance
time

Question 23

what is the equation for X-ray attenuation

Answer 23

I = Io e^(-ux)

I = radiation intensity after shielding
Io = radiation intensity before shielding
u = linear attenuation coefficient 
x= thickness of shielding material (cm)

Question 24

what is the linear attenuation coefficient

Answer 24

the constant that describes the fraction of x-ray photons that are absorbed or scattered per unit thickness of a material

Question 25

which is more attenuating - soft tissue or bone?

Answer 25

soft tissue

Question 26

what does it mean in terms of preventing penetration of x-ray beams if there is a High linear attenuation coefficient

Answer 26

High linear attenuation coefficient = more effective at removing x rays and stopping them from passing though materials

Question 27

what is the HVL

Answer 27

the thickness of material required to reduce the intensity of a radiation beam by half

Question 28

what is the equation for HVL

Answer 28

HVL = ln(2)/u = 0.693/u

Question 29

what is the relationship between HVL and u

Answer 29

inverse

Question 30

HVL changes with what?

Answer 30

Half value changes with energy

HVL increase as x ray energy goes up

Question 31

what is the inverse square law

Answer 31

x-ray intensity is inversely proportional to the square of the distance from the source

I is proportional to 1/d^2

Question 32

what is the equation used when comparing the x-ray intensity at 2 distances

Answer 32

I2/I1 = (d1)^2/(d2)^2

Question 33

what is exposure control in terms of distance

Answer 33

small changes in distance and location can make a significant difference to cumulative dose recieved

Question 34

what is the principle of justification

Answer 34

any decisions that alters the radiation exposure situation should do more good than harm

Question 35

what is the principle of optimisation of protection

Answer 35

the likelihood of incurring exposure the number of people exposed and the magnitude of their individual doses should all be kept as low as reasonably achievable taking into account economic and societal factors

Question 36

what is the principle of application of dose limits

Answer 36

total dose to any individual from regulated sources in planned exposure situations other than medical exposures of patients should not exceed the appropriate limits specified by the commission

Question 37

what is the purpose of structural shielding of imaging facilities

Answer 37

limit radiation exposures of employees and members of the public to acceptable levels

Question 38

what do the primary and secondary exposure of an individual in an adjacent area to be protected mainly depends on what 5 factors

Answer 38

the amount of radiation produced by the source

the distance between the patient and the radiation source

time spent in adjacent area

the amount of protective shielding between sources and individual

distance between source and the individual

Question 39

what 3 factors are considered the structural shielding of imaging facilities

Answer 39

location of x-ray sources

orientation and location of x-ray beam for various acquisitions

adjacent areas with typical occupancy and shielding design goals

Question 40

in terms of primary and secondary radiation, the barrier thickness is a function of which equation

Answer 40

N x T/(P x d^2)

T = how many people are there at one time
P = goal of how small do you want to limit it to
N = # of patients per week
D = distance (meters) from radiation source

Question 41

what are the DRLs and what are they

Answer 41

diagnostic reference levels

radiation dose levels for typical x-ray examinations for standard sized patients using standard equipment