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Unformatted text preview: 55 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 yl, 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 yl, The total decay constant is A = Ap+ + AEC = 0.2664 yl 7. The activity of a radioisotope is found to decreaseby 30% in one week. What are the values of its (a) decayconstant, (b) halflife, 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 103 h1
July 24, 2002 = 5.90 X 107 Sl ...
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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).
 Spring '06
 CADY

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