HW5-5-7a - 5-5 The averagelifetime is -1 t = "X=...

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Unformatted text preview: 5-5 The averagelifetime is -1 t = "X= 1.86 X 10 y. 9 From Fig. 5.5, the probability of /3+ decayis 0.8984+ 0.00006 = 0.8990. Thus the decay constant for positron decayis >'{J+ = 0.8990 x>. = 0.2395 y-l, From Fig. 5.5, the probability of electron capture is 0.101, Thus the decay constant for positron decayis Afj+ = 0.101 x A = 0.0269 y-l, The total decay constant is A = Ap+ + AEC = 0.2664 y-l 7. The activity of a radioisotope is found to decreaseby 30% in one week. What are the values of its (a) decayconstant, (b) half-life, and (c) mean life? Solution: (a) From the radioactive decay law A(t)jA(O) = exp( -At), upon solving for t, the time required to reach a specified value of A(t)jA(O) is 1 t = -A In [ A(O) ] . A(t) Here we are given A(t = 1 wk)/A(O) = 0.7. From the above result we find 2.12 X 10-3 h-1 July 24, 2002 = 5.90 X 10-7 S-l ...
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This note was uploaded on 02/01/2010 for the course ECE 4130 taught by Professor Cady during the Spring '06 term at Cornell University (Engineering School).

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