Radioactive `138I` has a half-life of 8.0 days .A sample containing `138I` has activity `20 mu Ci`at t=0.(a) What is its activity at t=4.0 days?(b) What is its decay constant at t=4.0 days?

Answer

A, B, C, D

Explanation

Given ` t_(1/2) = 8.0 days` ,
` A_(0) = 20 mu Ci `
` (a) t = 4.0 days , lambda = (0.693)/(8) `
`:. A = A_(0) e^(-lambda t) `
` = 20 xx 10^(-6) xx e^((-0.693)/(8) xx 4) `
` = 1.41 xx 10^(-6) Ci = 14 mu Ci `
` (b) lambda = (0.693)/([8 xx 24 xx 3600)] `
`= 1.0026 xx 10^(-6)`.