Question

A radioactive isotope has initial activity of `28` dpm Its activity is reduced to `14` dpm after half an hour. The initial number of nuclide in sample was:
A. `200`
B. `400`
C. `600`
D. `1211`

Answer 1

Correct Answer - `(d)`
Rate `= lambda N`, Also `t = (2.303)/(lambda) log ((r_(0))/(r))`,
`:. 30 = (2.303)/(lambda) log ((28)/(14))`
or `lambda = (2.303)/(30) xx 0.3010`,
No `28 = (2.303xx0.3010)/(30) xx N`
`:. N = 1211` atoms