Answer to Question #282250 in Atomic and Nuclear Physics for BIGIRMANA Elie

Question

2. One (1) gram of aradioactive substance disintegrates at the rate of 3.7 × 1010 per

second. The atomic weight of the substance is 226. Calculate its mean life.

Answer 1

1) Write down the expression for activity of the substance:

$$A=\frac NT.$$

2) Remember what the number of particles is:

$$N=nN_a=\frac mMN_a.$$

3) Express the time:

$$T=\frac{N}A=\frac{mN_a}{MA}=\frac{1·6.02·10^{23}}{226·3.7·10^{10}},\\\space\\ T=7.2·10^{10}\text{ s}.$$