Question

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The 137Cs source used for gamma rays in the Compton scattering experiment has a half-life of 30.17 years. Suppose that the initial absolute activity of a source N years ago was lo 5.46 mCi (milli-Curies) 202 million disintegrations/s. Suppose that the initial absolute activity of the 137Cs source (lo 5.46 mCi) occurred N-16.3 years ago. The expected absolute activity today, N years later, is mCi. mci You want to deduce the total gamma-ray activity from the 137Cs source without overwhelming the photomultiplier tube (PMT). The procedure is to shield most of the PMT using a brick that allows gamma rays through only a small circular window of diameter D 1.27 cm. You place the 137Cs source at a distance of R 33.0 cm from the window. Assume that the source sends gamma rays equally in all directions, so that the small area of the window greatly reduces the photon flux into the PMT. The PMT measures a count rate of a 0.012 million disintegrations/s. You deduce that the total gamma-ray activity from the 13 Cs source is A- disintegrations/s million

Answer 1

2 0. 693 112 63 3 R(+) = 3.2548 m Ci

PMT 33 Cm PMT 0. 012million tatal Phatan 2 disl see 12.9 . 64. mullon dis/se