Question

The half-life of a radiosotope is four hours. If the initial rate of the isotope was 200 dpm , the rate after 24 hours is:

• A. 6.25 dpm
• B. 2.084 dpm
• C. 3.125 dpm
• D. 4.167 dpm

Answer 1

Answer: (C)

3.125 dpm

We have,

$\frac{t_1}{2}$=4 hours

$N=\frac{\frac{T}{t_1}}{2}$=$\frac{24}{4}$

$=6$

N=$N_0(\frac{1}{2}{)}^n$ where n is the haf life

$N=200(\frac{1}{2}{)}^6$

$=\frac{200}{64}$=3.125 dpm