Detection and Measurement Flashcards

Which statement best describes the response of an ionization chamber survey meter in a pulsed radiation field (such as near an accelerator)?

Answer: It may over-respond due to ion collection efficiency losses at high instantaneous dose rates

High instantaneous dose rates in pulsed fields can cause ion recombination before collection, reducing ion collection efficiency and causing the meter to over- or under-respond depending on design.

The 'backscatter peak' seen in a gamma-ray spectrum is caused by:

Answer: Photons that Compton-scattered backward from shielding and entered the detector

Photons scattered at approximately 180° from surrounding materials enter the detector with reduced energy (~200-250 keV), creating a backscatter peak at the low-energy end of the spectrum.

For measuring skin dose (shallow dose equivalent, Hp(0.07)), the dosimeter placement and sensitivity should be optimized for:

Answer: Low-energy beta particles and photons in the first 0.007 cm of tissue

Hp(0.07) quantifies dose to the sensitive basal layer of skin at 0.007 cm depth, so detectors must respond to the low-energy beta and photon radiation that deposits dose in this shallow layer.

A portable X-ray fluorescence (XRF) analyzer used for radionuclide identification operates on which principle?

Answer: Exciting atoms with primary X-rays or gamma rays and detecting characteristic secondary X-ray emissions

XRF excites atomic electrons to higher energy levels; when they return to ground state, they emit characteristic X-rays whose energies uniquely identify the elements and sometimes isotopes present.

Electronic personal dosimeters (EPDs) are primarily used in addition to passive dosimeters because they:

Answer: Provide real-time dose rate and accumulated dose readout during the work task

EPDs provide immediate feedback on dose rate and cumulative dose, allowing workers and supervisors to make real-time decisions to stay within dose constraints during a task.

The 'figure-8' or 'dumbbell' angular response pattern of a directional gamma detector indicates:

Answer: Maximum sensitivity when radiation is incident along the detector axis and minimum at 90°

A figure-8 response pattern means the detector is most sensitive to radiation coming from the front and back (axial directions) with reduced response to side-incident radiation.

When using a multi-channel analyzer (MCA) for gamma spectroscopy, the gain setting determines:

Answer: The relationship between pulse amplitude and channel number, setting the energy range displayed

MCA gain maps pulse amplitudes (proportional to photon energy) onto the channel number scale, so changing the gain adjusts the energy range and resolution of the displayed spectrum.