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HW6-18 - 5-13 18 The averagemass of potassium in the human...

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5-13 18. The average mass of potassium in the human body is about 140 g. From the abundance and half-life of 40K (see Table 5.2), estimate the average activity (Bq) of 40K in the body. Solution: From Table 5.2, the atomic abundance of40K is 140 = 0.000117. The number of potassium atoms in the body N K is N K = ~ = .(140)(6.022 X 1023) = 2.156 X 1024 atoms. 39.0983 The number of 4oK atoms is N40 = 0.000117NK = 2.523 X 1020 atoms. This number of 4oK atoms has an activity A40 = A40N40. The decay constant for 40K is In2 A40 = - T = 1.73 X 10-17 S-1 1/2 Thus the 40K activity in the body is A40 = A40N40 = (1.73 x 10-17)(2.523 x 1020) = 4,360 Bq. 19. The naturally occurring radionuclides 222Rn and 220Rndecay by emitting a particles which have a range of only a few centimeters in air. Yet there is con- siderable concern about the presence of these radioisotopes in interior spaces. Explain how these radioisotopesenter homes and workspaces and why they are
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