dosimetry equipment

Question 1

what is Hp(d)

Answer 1

personal dose equivalent

Question 2

what is short for personal dose equivalent

Answer 2

Hp(d)

Question 3

what is Hp(0.07)

Answer 3

skin dose

Question 4

what is Hp(3)

Answer 4

lens of eye dose

Question 5

what is short for dose to lens of eye

Answer 5

Hp(3)

Question 6

what is short for dose to skin

Answer 6

Hp(0.07)

Question 7

how can Hp(d) be measured

Answer 7

dosimeter at surface of body covered with an appropriate layer of tissue equivalent material

Question 8

what kind of quantity is personal dose equivalent

Answer 8

operational

Question 9

essential design of a good dosimeter 6

Answer 9

1. it can detect radiation
2. relevant dose quantity
3. appropriate range (energy/dose and doserate)
4. linear response with dose
5. flat response with energy and doserate

Question 10

how does an ion chamber work

Answer 10

air in chamber at natural atmospheric pressure
air ionised by the radiation and charge pairs accelerated across high voltage field between two electrodes
current proportional to dose`

Question 11

ion chamber good (4)

Answer 11

linear response across large dynamic range

can vary chamber size for specificity/spatial res

stable over time

dose accumulates

Question 12

ion chamber bad (3)

Answer 12

electrometer used for readout limited by leakage current

requires temp/pressure corrections

requires careful calibration

Question 13

GM tubes how they work

Answer 13

sealed chamber with low pressure gas
ion pairs created
acceleration of electrons by high voltage cause further ionisation (chain reaction) of gas molecules and large pulse measured

Question 14

what unit does GM tube measure in

Answer 14

current per second
can be calibrated to microSV/hr within specific energy range

Question 15

GM tubes good (4)

Answer 15

greater sensitivity

detection of all radiation types

low dose measurements

cheap

Question 16

GM tubes uses (2)

Answer 16

spillages, monitoring

Question 17

GM tubes bad (2)

Answer 17

dead time - poor at high doserates - means that indicated rate is lower than actual

poor energy response output (pulse the same regardless of energy)

Question 18

what is dead time

Answer 18

insensitive period after each ionisation of the gas where further ionising radiation will not result in a current

Question 19

what scintillation detectors use as detector material

Answer 19

phosphor

Question 20

how do scintillation detectors work

Answer 20

when irradiated give of flash of light

amplified by PM tubes and measured

Question 21

why do scintillation detectors give off a flash of light when irradiated

Answer 21

because of their arrangement of outer shell electrons

Question 22

why are GM tubes and scintillations greater sensitivity

Answer 22

can detect individual events

Question 23

what are scintillation devices used for

Answer 23

low level radiation

Question 24

what must scintillation material match

Answer 24

radiation type

Question 25

scintillation device good

Answer 25

sensitivity - low level measurement can determine the energy of the radiation through the size of the pulses

Question 26

scintillation device bad

Answer 26

must match radiation type

Question 27

how do semiconductor detectors work

Answer 27

radiation produces free electrons and holes ion the detector electric field applied and electrons and holes travel to electrodes on either sides of the detector this results in a measurable voltage pulse

Question 28

what is the number of electron hole pairs proportional to

Answer 28

the energy of the radiation

Question 29

what does irradiation of TLD cause to happen to electrons

Answer 29

they get stored in a meta stable state within the crystal structure (latent signal)

Question 30

how are stored electrons released from traps inside TLD crystal

Answer 30

heated to a few hundred degrees

Question 31

what happens when electrons are released from TLD crystal traps

Answer 31

series of light scintillations which can be measured using PM tubes

Question 32

two uses of luminescence (e.g. TLD) dosimetry

Answer 32

personal monitoring RT patient dose monitoring

Question 33

what happens when gafchromic film exposed to radiation

Answer 33

dye changes colour

Question 34

what can be characterised using gafchromic film

Answer 34

level of exposure beam shape

Question 35

advantage of gafchromic film over conventional x ray film development

Answer 35

no developing process - instant results

Question 36

disadvantage of gafchromic film

Answer 36

poor response below 1cGy

Question 37

what is gafchromic film useful for

Answer 37

RT and primary beam