Question

Calculate the activity of a pure 7.4-μg sample of 3215P (T12=1.23×106s).

Answer 1

one may use the definition of activity, which is: A = λN, where λ is the decay constant, and N is the number of atoms.

λ = 0.693/ haf life

λ = 0.693/ 1.23×10^6

λ = 0.5634 *10^-6 /s

Activity , A = λ *N

N is the number of atoms

1 mole is equal to 1 moles Phosphorus, or 30.973761 grams.

7.4*10^-6 gms contain (1/30.973 )*7.4*10^-6 moles = (1/30.973 )*7.4*10^-6 * 6.023*10^23 = 1.439*10^17 atoms

So, N = 1.439*10^17 atoms

Activity , A = λ *N = 0.5634 *10^-6 * 1.439*10^17 = 0.810*10^11 dps