- A radioactive sample has two g-ray photons of 130- and 120-keV ener-
gies. If a NaI(Tl) crystal has an energy resolution of 10% at 125 keV,
could the two photons be detected as separate photopeaks? - Both gas-filled detectors and semiconductor detectors operate by ion-
ization of atoms by radiation. Why do semiconductor detectors give
better energy resolution than gas-filled detectors? - A patient is given orally a 10-mCi^131 I-NaI capsule. Before administra-
tion, the count rate of the capsule in a thyroid phantom is 297,000 cpm.
The 24-hour count rate of the patient’s thyroid is 168,000 cpm. If
the room background is 200 cpm and the patient’s thigh count rate is
1000 cpm, calculate the thyroid uptake. - High-activity sources such as radiopharmaceutical dosages and x-ray
exposure outputs are better measured with ionization chambers than
GM counters and NaI(Tl) well counters. Why? - Which of the following counters can detect individual events of the
radiation interacting with the detector?
(a) Ionization chamber
(b) GM counter
(c) NaI(Tl) well counter - What type of Compton scattering causes the Compton edge of a g-ray
spectrum? - Discuss the properties of newer detectors. Explain why BGO is prefer-
ably used in PET cameras.
Suggested Readings
Bushberg JT, Seibert JA, Leidholdt EM Jr, Boone JM.The Essential Physics of
Medical Imaging. 2nd ed. Philadelphia: Lippincott Williams & Wilkins; 2002.
Cherry SR, Sorensen JA, Phelps ME.Physics in Nuclear Medicine. 3rd ed. Philadel-
phia: W.B. Saunders; 2003.
Cradduck TD. Fundamentals of scintillation counting.Semin Nucl Med. 1973;
3:205–223.
Hendee WR, Ritenour ER.Medical Imaging Physics. 4th ed. New York: Wiley-Liss;
2002.
Hine GJ. Sodium iodide scintillators. In: Hine GJ, eds.Instrumentation in Nuclear
Medicine. New York: Academic Press; 1967;I:95–117.
Peng CT, Horrocks DL, Alpen EL, eds.Liquid Scintillation Counting. New York:
Academic Press; 1980; I, II.
Rollo FD, ed.Nuclear Medicine Physics, Instrumentation and Agents. St. Louis:
Mosby; 1977.
Suggested Readings 107