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Part II > Instrumentation and measurement trivia > Flashcards

Instrumentation and measurement trivia Flashcards

1
Q

The function of a cascade impactor is to seperate

A

Particles according to mass

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2
Q

Purpose of an ‘annular kinetic impactor head’ is to trap

A

Airborne particles. Does not collect radon and thoron

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3
Q

What scintillator material has a high efficiency for alpha measurement?

A

ZnS. NaI is used for gamma spec.

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4
Q

Approximate efficiency for radioiodines on an activated charcoal filter at the appropriate flow rate

A

95%

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5
Q

Disadvantage of a long sample counting time for optimization of counting statistics?

A

Background may change

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6
Q

Approximate eifficiency for the detection of Xenon-133 on activated charcoal

A

1%. It is a noble gas, so it doesn’t want to interact with anytihng

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7
Q

Primary function of proportional counters is to

A

Measure and distinguish alpha from beta

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8
Q

A low energy alpha detector is usually effective if the detector is _____ distance from the source

A

1/4 inch. Low energy alphas can only travel less than 1/2 inch in air

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9
Q

Proportional counters have gas amplification that are

A

greater than 1.

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10
Q

Ion chambers have gas amplification factors of:

A

equal to 1

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11
Q

A proportional counter has enough voltage to cause

A

Secondary electrons with short range avalanche

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12
Q

What radiation instrument operates on the principal of discharging of a capacitor to estimate radiation dose?

A

Pocket ion chamber

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13
Q

An ionization chamber has voltage great enough to cause

A

Ions before recombination; no secondary electrons

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14
Q

A geiger counter has enough voltage to cause

A

Secondary electrons with a long range avalanche

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15
Q

A scintillation counter takes advantage of properties of materials that _____, after being exposed to energy from radioactive sources

A

Fluoresce

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16
Q

Semi-conductor detectors are used primarily for their:

A

High energy resolution

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17
Q

Cost effective means available to test for radon gas in a building

A

Alpha track detector, Charcoal cannister

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18
Q

Very thin windowed GM detectors can detect what types of ionizing radiation

A

Alpha, Beta, Gamma

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19
Q

Full Width Half Maximum (FWHM) of the photopeak is a measurement of

A

Resolution

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20
Q

What is the effective half life in the human body for Co-60, if the biological half-life is eight days?

A

7.97 days. The effective half-life is never greater than the biological half-life. Teff= (Tb*Tr)/(Tb+Tr)

21
Q

Absolute efficiency

A

Number of pulses recorded/number of radiation quanta emitted by source

22
Q

Intrinsic efficiency

A

Number of pulses recorded/number of radiation quanta incident on the detector

23
Q

Relationship between E-absolute and E-intrinsic

A

E-Intrinsic = E-absolute * (4(pi)/Solid angle of detector)

24
Q

% resolution formula for photo-peaks

A

% resolution = (FWHM/Energy Peak)*100

25
Q

Constituents of fill gas P-10

A

90% argon 10% methane. Used in gas-filled detectors in the proportional and G-M regions. The argon serves as the ionization gas, the methane is an organic quench gas.

26
Q

Formula for standard deviation in counting

A

1 Sigma = (Sample Count Rate/Sample Count Time)^1/2

27
Q

Quality factor is a function of the

A

Collision stopping power of the radiation in water

28
Q

Why is sulfur used in criticality accident dosimetry?

A

The S-32(n,P)P-32 reaction produces measurable beta activity.

29
Q

Resolving time/Dead time correction

A

True count rate = recorded count rate/(1-Recorded rate*dead time)

30
Q

Isokinetic sampling

A

Constant velocity sampling. V1(D2)^2=V2(D1)^2

31
Q

95% confidence level

A

2 sigma= 1.96[(bkg rate /time)+(sample rate /sample time))]^.5

32
Q

What is the ionizing region

A

The region of voltage over which the saturation current is produced. Saturation current is when one electron reaches the detector electrode for each electron released by ionization in the detector.

33
Q

What instrument has a good sensitivity to neutrons while providing the best discrimination against gammas?

A

BF-3 proportional counter in polyethylene moderator. The proportional region of the detector is set at an alpha voltage to detect the B-10(n,alpha)Li-7 reaction.

34
Q

The most energetic Compton electron results from a 180 degree backscatter of the incident photon. This electron is called

A

Compton edge.

35
Q

Compton edge will occure at _____ of the photopeak energy

A

Photopeak energy - 250 keV

36
Q

To avoid excessive dead time on multi-channel gamma analyzers you should keep samples below:

A

10mR/hr at 2 inches.

37
Q

A semi-conductor is distinguished from an insulator or conductor by its:

A

Band Gap. Insulator gaps are large, 5 eV or more. In a semi-conductor the gap is in the range of 0.7-2.1 eV

38
Q

Dead time for proportional counters is approximately:

A

0.5 microseconds. GM counter dead times can exceed 100 microseconds.

39
Q

A sample with mixed alpha and beta emitting nuclides is counted with a gas flow proportional counter at the alpha voltage (A) and at the beta voltage (B). The alpha and beta count rates, respectively, may be estimated from these count rates as:

A

A and B-A

40
Q

Usual FWHM for the Cs-137 photopeak is

A

50 keV

41
Q

The term “tissue Equivalent” when used to describer ionization chamber construction means that theRev. 1

A

Chemical composition of the wall material and gas filling the ion chamber are selected such that the response of the ion chamber will be a measure of the absorbed dose in tissue

42
Q

A polyethylene-walled ion chamber filled with ethylene gas willRev. 1

A

Measure the absorbed dose from photons and will give an over-estimate of the absorbed dose from neutrons

43
Q

Initial recombination of ion pairs produced in an ionization chamber gas isRev. 1

A

Independent of dose rate. Recomb depends on LET

44
Q

Volume recombination (recombination during drift towards electrodes) in the ion chamber gas isRev. 1

A

Dependent on dose rate

45
Q

Initial recombination in a high pressure tissue equivalent ionization chamber can be used to:Rev. 1

A

Determine the average quality factor in a mixed neutron and photon field. (think LET dependence)

46
Q

The number of ion pairs collected in an air-filled aluminum walled ionization chamber depends primarily on:Rev. 1

A

Absorbed dose rate

47
Q

Ion pair collection in ionization chambers used to monitor pulsed radiation depends on:Rev. 1

A

Ion pairs produced during the pulse

48
Q

An aluminum ion chamber filled with CO2 will best measure:Rev. 1

A

the high energy neutron fluence in mixed radiation fields.

49
Q

The efficiency for collecting ion pairs produced in an ionization chamber is greater using:Rev. 1

A

Parallel plate electrodes. (electrical field is stronger compared to cylindrical or spherical electrodes)

Part II (25 decks)

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