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Huda > Chapter 6 Radiation Protection > Flashcards

Chapter 6 Radiation Protection Flashcards

1
Q

explain how solid state dosimeters work

A

-crystals store energy absorbed during expsure in electron traps
-in TLD, these electrons are released by application of heat and release visible light
-OSLD use laser light to release stored energy
-OSLD can be read out several times whereas TLD can only be read out once
-can measure 0.01 mGy to 10,000 mGy

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2
Q

typical TLD material in radiology

A

lithium fluoride
reponse independent of x-ray energy

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3
Q

explain how ion chambers work

A

measure charge liberated when x-ray photons ionize the gas inside the chamber
-anode is used to collect electrons; need large enough voltage
-not very sensitive but very accurate

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4
Q

explain how geiger counters work

A

-ion chamber with very high voltage across chamber
-incident photon interaction produces small number of free electrons, which are accelrated towards the positive anode, gaining energy
-energetic electrons cause more electrons to be ejected from gas atoms, which are also accelerated, ejecting more electrons (i.e. avalanche)
-any incident beta particle or photon results in similar signal
-very sensitive, used to detect contamination
-each detected photon gives a click
-cannot measure dose rate or tube output, same response regardless of incident photon or particle energy

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5
Q

explain pocket dosimeters

A

ion chambers that look like large pens
-use a positively charged quartz fiber suspended in an air-filled chamber
-x-rays incident on chamber produce ions that neutralize the charge and cause the fiber to move
-0-2 mGy
-can be recharged
-gives immediate readings

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6
Q

what types of doses are measured for radiation workers?

A

-skin dose (shallow)
-eye lens dose (can use dosimeter on glasses)
-deep dose

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7
Q

convert mrem to mSv

A

100 mrem = 1 mSv

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8
Q

for what time period is worker exposure recorded?

A

current period
current quarter
current year
lifetime

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9
Q

what is NCRP

A

National committee council on radiological protection and measurements

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10
Q

what does NCRP recommend we take as the effective dose to the worker (from the dosimeter)

A

0.18 of the dose recorded by dosimeter worn on collar
if worker also wears dosimeter on waist then, 1.5 Hwaist + 0.04 Hcollar

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11
Q

good way to estimate dose to extremities

A

dosimeter on a finger

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12
Q

regulatory organizations

A

ICRU (International commission on radiological units and measurements)
UNSCEAR (UN Scientific committee on effects of atomic radiation)
BEIR (National academy of sciences committee on biological effects of ionizing radiation)
ICRP (International commission on radiological protection)
NCRP (National Council on radiation protection)
NRC (Nuclear regulatory commission) - responsible for regulating radioactive materials in US

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13
Q

occupational dose limits

A

-exclude those from medical exams or background radiation
-100 mSv/5 years with no more than 50 mSv in a given year
-NCRP uses lifetime effective dose limit of 10 times the individual’s age

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14
Q

tyoical dose actually received by radiation workers

A
  • 5 mSv/year unless emergency occupational exposure
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15
Q

eye lens dose limit for radiation worker

A

-150 mSv/year
-2011 ICRP recommended reducing it to 20 mSv/year but not many countries have adopted this

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16
Q

skin dose limit for radiation worker

A

500 mSv/year
-skin doses are to be averaged over the most highly exposed 1 cm2

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17
Q

extremity dose limit for radiation worker (ex hands)

A

500 mSv/year

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18
Q

dose limit for members of public

A

1 mSv/year
-excludes natural background radiation and medical tests

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19
Q

dose limit for pregnant workers

A

0.5 mSv/month during pregnancy (5 mSv total)
monitored by dosimeter worn on abdomen

In Canada 4 mSV for duration

20
Q

US population average dose from diagnostic medical exams

A

3 mSv
-population doses from diagnostic radiology increased 6 fold in one generation
-CT scans account for 17 % of diagnostic x-ray exams, but half the population medical dose

21
Q

what is DAM

A

Don’t order tests that don’t affect management
-patient medical exams have to be justified

22
Q

ALARA

A

As low as reasonably achievable
-eliminate unecessary radiation
-eyes, lens, gonads, and breasts may be shielded for some applications
-decrease exposure time, increase distance, use shielding

23
Q

medical exams on pregnant women

A

-when x-ray beam does not directly irradiate the fetus or embryo, the corresponding dose will be low
-if a woman has exam and is unaware she is pregnant:
-no medical action for unintended dose up to 100 mGy as risks are low compared to pregnancy
-high doses during organogenesis may warrant consideration of abortion

24
Q

what is radiation protection in workers designed to do (2 things)

A

-prevent deterministic effects
-reduce stochastic risks

25
Q

what is scatter dose level from patients at 1 m?

A

0.1% of entrance skin dose

26
Q

benefit of using last minute hold technique during fluoro

A

patients receive no radiation exposure

27
Q

ways to reduce exposure during fluoro

A

-last minute hold technique
-pulsed fluoro rates of 15 frames/s or less
-reduce number of spot images or photospot images where possible
-maximize distance between worker and source
-because of IS law increasing distance is more effective than reducing exposure time

28
Q

how much Pb do x-ray rooms usually contain in their walls?

A

1.6 mm (2 m)

29
Q

what is more effective? shielding, time or distance?

A

shielding
then distance
then time

30
Q

60 kV Pb HVL and TVL

A

0.1 mm and 0.35 mm

31
Q

80 kV HVL and TVL

A

0.2 mm and 0.65 mm

32
Q

130 kV HVL and TVL

A

0.3 mm and 0.9 mm

33
Q

sources of workers radiation dose

A

-dose to 90% of x-ray technologists are below detection limit
-sources of doses include fluoro, interventional radiology, nuclear medicine

34
Q

fluoro worker yearly dose

A

1 mSv

35
Q

nuc med worker yearly dose

A

2-3 mSv

36
Q

how thick are Pb aprons

A

0.25 or 0.5 mm
less effective for higher energies

37
Q

dose nuclear power workers get yearly

A

5 mSv

38
Q

dose air crew workers get yearly

A

5 mSv

39
Q

US public exposure from consumer products and activities per year

A

0.1 mSv
-a third is from tobacco
-a quarter is from radioactivity in building materials
-another quarter is from commercial aviation

40
Q

medicine and aviation account for what % of the population dose from occupational exposure?

A

80%

41
Q

what do occupational doses contribute to US population doses per year?

A

0.01 mSv

42
Q

what does nuclear fuel cycle contribute to US population dose per year?

A

< 0.01 mSv

43
Q

patient skin dose for lateral skull x-ray

A

1 mGy

44
Q

patient skin dose for 1 min fluoro

A

10 mGy

45
Q

patient skin dose for CT scan

A

40 mGy

Huda (20 decks)

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