Physics U3 (Rad Protection & Equipment)

exposure

number of ionizations in air

how is exposure measured?

Coulombs per kilogram (C/kg)

air kerma

energy of ionizations in air

how is air kerma measured?

gray (or joules/kg)

what is air kerma useful for?

measuring tube output, leakage radiation and scatter

absorbed dose

the amount of energy absorbed per unit mass

how is absorbed dose measured?

gray (or joules/kg)

what is absorbed dose useful for?

predicting short term radiation injuries

equivalent Dose (EqD)

takes into consideration the type of ionizing radiation that was absorbed

How is equivalent dose determined?

absorbed dose x Wr (weight factor)

what is equivalent Dose measured in?

sieverts

effective dose

takes into consideration the relative radiation sensitivities of different tissue types

what is effective dose used for?

to predict the risk of long term radiation induced injuries

what is effective dose measured in?

sieverts

whole body exposure limits

5 rem/yr (50 mSv)

who is personnel monitoring provided to?

workers who accumulate 1/10 of recommended dose limit

where should devices be worn?

collar, waist, or ring

dosimetry

measurement of ionizing radiation doses to personnel

what detector is used in OSL badges?

aluminium oxide

how is an OSL processed?

using laser light to cause luminescence

disadvantage of OSL

expensive

what detector is used in TLD badges?

lithium fluoride crystals

how are TLDs processed?

released stored energy when heated as visible light

disadvantage of TLDs

sensitive to heat

disadvantage of pocket dosimeters

poor accuracy, must be recharged

purpose of dosimetry report

provide personnel with regular feedback reguarding protection practices

primary barriers

protect against direct exposure to the primary beam

secondary barriers

scatter and leakage radiation

cardinal principles of radiation control

time, distance, shielding

beam limitation

1/2 inch of collimation, field size never larger than IR

how can we minimize dose w technique?

highest kVp, lowest mAs

filteration

removes low energy photons

where is a filter placed?

between tube and patient

where are grids placed?

between the patient and IR

what grid ratio should be used?

the lowest possible

when is the fetus most radiosensitive?

8-15 weeks of gestation

pregnancy dose limit

0.5 rem if declared