HW15-8 - Si(Li), or CZT for (a) lOO-keV gamma rays, and (b)...

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8. If the energy resolution of a NaI(TI) detector is 8%, what is the FWHM of the full-energy peak for a 137Cs source? Solution: NOTE: Chapter 8 does not define resolution although it is discussed frequently. Consequently, this question is somewhat beyond the text. The resolution of a spectroscopic energy peak is define as Res(%) = 100 ~~ Emax where Emax is the energy at the which the peak is a maximum and FWHM is the width of the peak at one-half the maximum height. From Ap. D, 137Cs emits a 0.662 MeV gamma ray. This the FWHM of the 0.662-MeV peak in a N aI spectrum is 8 ~~ = 0.662 - 100 FWHM = Ernax = 0.00662 MeV. 9. Which detector has the greatest full-energy peak efficiency: NaI(TI), HPGe,
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Unformatted text preview: Si(Li), or CZT for (a) lOO-keV gamma rays, and (b) for I-MeV gamma rays? Justify your answer. Solution: The full-energy peak efficiency is the probability an incident gamma ray will interact in the crystal and also deposit all its energy in the crystal (i.e., no secondary radiation escapes). Thus, the efficiency is the product of (1) the probability Pint the gamma ray interacts at all and (2) the probability Pdep that the interaction leads to total energy deposition in the crystal. The probability of interaction is Pint ~ 1 -e-IJ.X where x is the crystal thickness and JL the total interaction coefficient. July 24, 2002...
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