(b) A photopeak is due to only photoelectric effect of g-rays, or due to
all g-rays that deposit full energy in the detector. True or false?- (a) Describe the function of a pulse-height analyzer (PHA).
(b) Do the following factors affect the size (pulse height) of the pho-
topeak pulses?
i. Gain of the amplifier
ii. High voltage of PM tubes
iii. Distance between the source and the detector
iv. Light photons produced in the detector - In a g-ray spectrum, describe the origins of:
(a) Backscatter peak
(b) Compton valley
(c) Characteristic Kx-ray peak
(d) Iodine escape peak
(e) Sum peak - (a) Describe the principles of a liquid scintillation counter.
(b) What is a scintillation solution, and how does it work?
(c) What is the purpose of using a secondary solute to the scintillation
solution?
(d) What are the most common solvents for liquid scintillation
counting?
(e) Can you count^3 H (b−energy =0.018 MeV) and^14 C (b−energy =
0.156 MeV) in the same sample using a liquid scintillation counter
equipped with three PHAs? - (a) Define the energy resolution of a detector.
(b) For a given detector, the energy resolution of low-energy photons
is poorer than that of high-energy photons. True or false?
(c) For NaI(Tl) detectors, the energy resolution should be less than
10% for the 662-keV photon of^137 Cs. True or false? - (a) A point source of 99mTc is placed 10 cm away from a NaI(Tl) detec-
tor that has a diameter of 20 cm. Calculate the geometric efficiency.
(b) What would be the geometric efficiency if the source were placed
on the surface of the detector? - (a) Explain the dead time and pulse pileup of a counter.
(b) What is the distinction between the paralyzable and nonparalyz-
able systems?
(c) What are the typical dead times for Geiger–Müller (GM) counters
and NaI(Tl) counters? - (a) Describe the energy calibration of a NaI(Tl) well counter.
(b) Why does the count rate differ from the disintegration rate of a
sample of a radionuclide?
(c) How does the sample volume affect the count rate? - What are the spillover or crosstalk contributions in a spectrum of
several g-rays? How would you correct for them?
106 8. Scintillation and Semiconductor Detectors