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Flashcards in Instrumentation and Detection Deck (41):
1

The function of a cascade impactor is to seperate

Particles according to mass

2

Purpose of an 'annular kinetic impactor head' is to trap

Airborne particles. Does not collect radon and thoron

3

What scintillator material has a high efficiency for alpha measurement?

ZnS. NaI is used for gamma spec.

4

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

95%

5

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

Background may change

6

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

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

7

Primary function of proportional counters is to

Measure and distinguish alpha from beta

8

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

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

9

Proportional counters have gas amplification that are

greater than 1.

10

Ion chambers have gas amplification factors of:

equal to 1

11

A proportional counter has enough voltage to cause

Secondary electrons with short range avalanche

12

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

Pocket ion chamber

13

An ionization chamber has voltage great enough to cause

Ions before recombination; no secondary electrons

14

A geiger counter has enough voltage to cause

Secondary electrons with a long range avalanche

15

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

Fluoresce

16

Semi-conductor detectors are used primarily for their:

High energy resolution

17

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

Alpha track detector, Charcoal cannister

18

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

Alpha, Beta, Gamma

19

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

Resolution

20

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

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

21

Absolute efficiency

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

22

Intrinsic efficiency

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

23

Relationship between E-absolute and E-intrinsic

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

24

% resolution formula for photo-peaks

% resolution = (FWHM/Energy Peak)*100

25

% resolution formula for photo-peaks

% resolution = (FWHM/Energy Peak)*100

26

Constituents of fill gas P-10

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.

27

Formula for standard deviation in counting

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

28

Quality factor is a function of the

Collision stopping power of the radiation in water

29

Why is sulfur used in criticality accident dosimetry?

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

30

Resolving time/Dead time correction

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

31

Isokinetic sampling

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

32

95% confidence level

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

33

What is the ionizing region

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.

34

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

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.

35

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

Compton edge.

36

Compton edge will occure at _____ of the photopeak energy

Photopeak energy - 250 keV

37

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

10mR/hr at 2 inches.

38

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

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

39

Dead time for proportional counters is approximately:

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

40

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 and B-A

41

Usual FWHM for the Cs-137 photopeak is

50 keV