Detection and Measurement Flashcards
7 cards from real NRRPT practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Detection and Measurement flashcards as text
An OSL (optically stimulated luminescence) dosimeter differs from a TLD primarily in that it:
Answer: Uses light (laser) rather than heat to read out stored dose information
OSL dosimeters use laser light stimulation to release stored energy as luminescence, allowing non-destructive readout and the ability to re-read the same dosimeter multiple times.
The Compton edge in a gamma-ray pulse-height spectrum represents:
Answer: The maximum energy transferred to a recoil electron in Compton scattering
The Compton edge is the maximum kinetic energy a recoil electron can receive from Compton scattering, which occurs when a photon backscatters at 180 degrees.
What is the purpose of a moderator in a neutron rem meter (such as the Andersson-Braun rem meter)?
Answer: To slow fast neutrons to thermal energies where detection efficiency is higher
Moderating materials (typically polyethylene) slow fast neutrons through elastic scattering, converting them to thermal neutrons that are efficiently detected by the BF3 or He-3 tube.
A survey meter with a pancake probe is particularly useful for:
Answer: Detecting low-energy beta and alpha contamination on surfaces
The thin window on a pancake GM probe allows low-energy beta particles and alpha particles to enter the detector, making it ideal for surface contamination surveys.
The energy resolution of a germanium (HPGe) detector compared to NaI(Tl) is:
Answer: Significantly better, allowing discrimination of closely spaced gamma energies
HPGe detectors have energy resolution of ~0.1-0.2% FWHM compared to ~7% for NaI(Tl), enabling identification of radionuclides with very similar gamma-ray energies.
When performing a minimum detectable activity (MDA) calculation, the critical level (Lc) represents:
Answer: The net count above background at which a decision is made that a signal is present
The critical level (Lc) is a statistical threshold above which a measured count rate is considered to indicate the presence of radioactivity with defined probability of a false positive.
A portable alpha spectrometry system used for plutonium air sampling requires the sample to be:
Answer: Thin and dry to minimize alpha self-absorption within the sample
Alpha particles have very short ranges in matter, so thick or wet samples cause energy loss and self-absorption, degrading spectral resolution and reducing detected count rate.