A sample of radioactive element has a mass of 10g at an instant t=0. The approximate mass of this element in the sample after two mean lives is
1-1.35g
2-2.50g
3-3.70g
4-6.30g
t = 2 * tau(average or mean life) = 2 * 1.44T = 2.88T
As, N/N0 = m/m0 = (1/2)t/T = (1/2)2.88
Therefore, m = m0 (1/2)2.88 = 10 (1/2)2.88 = 10 * 0.1358 = 1.358 g .
As, N/N0 = m/m0 = (1/2)t/T = (1/2)2.88
Therefore, m = m0 (1/2)2.88 = 10 (1/2)2.88 = 10 * 0.1358 = 1.358 g .