Question

The activity of 1 mg sample of ${}_{37}S{r}^{90}$ whose half-life period is 28yr is

• A. 7.83x 10${}^{18}$ dps
• B. 6.69 x10${}^9$ dps
• C. 5.24x 10${}^9$ dps
• D. 6.69x 10${}^{18}$ dps

Answer 1

Answer: (C)

5.24x 10${}^9$ dps

Half life $=28years$
$\lambda =\frac{ln2}{28\times 365\times 24\times 3600}se{c}^{-1}$

$90$ grams of sr contains $6.022\times {10}^{23}atoms$

$1$ gram of sr contains $\frac{6.022}{9}\times {10}^{22}atoms$

$\frac{1}{1000}$ grams of sr contains $\frac{6.022}{9}\times {10}^{19}atoms$
Activity $=\lambda N=\frac{ln2\times 6.022\times {10}^{19}}{28\times 365\times 24\times 3600\times 9}dps$

$=5.25\times {10}^{9}dps$