Question

tetrahedral Si 92 230 30.975 26h How many hours are needed for a sample of Si - 31 with an activity of 20 Ci to decay to stry arch

Answer 1

Part L: As si - 31 is a radioactive sample so its activity varies with time as A = A_0 e^-lambda t equation (1) where A is activity of sample at time t A_0 is initial activity lambda is decay constant t is the time taken to decay. For radioactive si - 31, lambda = ln2/t_1/2 t_1/2 For si - 31 = 2.6 h Therefore lambda = ln 2/2.6 A = 2.0 mu ci A_0 = 20 mu c_1 Substituting in equation (1), we get 2 = 20 e^-(ln 2/2.6)t 1/10 = e^-(ln2/2.6)t t = 8.6 hrs