Radiation Measurement and Instrumentation Flashcards
7 cards from real CHP practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Radiation Measurement and Instrumentation flashcards as text
In pulse-height analysis, the 'full-energy peak efficiency' of a HPGe detector refers to:
Answer: The fraction of photons entering the detector that deposit all their energy in the active volume
Full-energy peak (or photopeak) efficiency is the fraction of gamma rays incident on the detector that are fully absorbed and contribute counts to the photopeak.
A scintillation detector's photomultiplier tube multiplies signal by using:
Answer: Secondary electron emission from a series of dynodes held at increasing positive voltages
A PMT amplifies the photoelectron current through successive secondary-emission dynodes, each held at a higher voltage, yielding typical gains of 10⁶–10⁷.
Which correction factor must be applied to an ionization chamber reading to account for changes in ambient conditions?
Answer: Temperature-pressure correction factor (kTP)
The temperature-pressure correction kTP = (273.15 + T) × P₀ / [(273.15 + T₀) × P] adjusts the air mass in the cavity to reference conditions.
The minimum detectable activity (MDA) of a measurement system is most directly improved by:
Answer: Reducing background count rate or increasing counting time
MDA is proportional to √(background counts) / counting efficiency; reducing background or counting longer both lower the MDA.
In neutron dosimetry, a rem meter (e.g., Andersson-Braun design) is constructed so that its response approximates:
Answer: The ICRP fluence-to-dose-equivalent conversion function for neutrons
Rem meters use polyethylene moderation and absorbing shells shaped to match the ICRP fluence-to-H*(10) conversion coefficients across a broad neutron energy range.
Gamma-ray buildup factors in shielding calculations account for:
Answer: Scattered photons that still contribute to dose at the detector point
Buildup factors correct for the fact that scattered (degraded-energy) photons still contribute to dose, causing actual dose rates to exceed the narrow-beam (uncollided) estimate.
An electret ionization chamber used for long-term radon measurement stores charge on a:
Answer: Permanently charged polymer disk (PTFE) that acts as a voltage source
The electret is a permanently polarized PTFE disk whose surface voltage decreases as ions produced by radon progeny neutralize it, and the voltage drop is proportional to cumulative exposure.