11) What is the length of the half-life in minutes, of anisotope, if after 1.00

Question

11) What is the length of the half-life in minutes, of anisotope, if after 1.00 hours, 20% of the starting materialremains? 12) A sample originally contained 50 Ci (microcuries) ofP-32. Today it contains only 15 Ci. If the half-life of P-32is 14.3 days, how old is the sample? 11) What is the length of the half-life in minutes, of anisotope, if after 1.00 hours, 20% of the starting materialremains? 12) A sample originally contained 50 Ci (microcuries) ofP-32. Today it contains only 15 Ci. If the half-life of P-32is 14.3 days, how old is the sample?

Explanation / Answer

[A] = [A_0] *exp(-k*t] [A]/[A0] = 0.20 = exp(-k*1 hr) k = 1.69 hr^-1 t_half = ln(2)/k = 0.431 hrs b) d[A]/dt = [A0]*exp(-k*t)*k k = ln(2)/ 14.3 = 0.0484718308 15 = 50*exp(-0.0485*t) t = ln(15/50)/(-0.0485) = 24.838608 days ~ 24.8 days

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