Discussion Forum



1)

The activity of a radioactive sample is measured as 9750 counts per minute at t = 0 and as 975 counts per minute at t = 5 minutes. The decay constant is approximately


A) 0.922 per minute

B) 0.691 per minute

C) 0.461 per minute

D) 0.230 per minute

Answer:

Option C

Explanation:

$\frac{dN}{dt} = KN$

$9750 = KN_{0}$ .....(i)

975 = KN  .................(ii)

Dividing (i) by (ii)

$\frac{N}{N_{0}} = \frac{1}{10}$

$K=\frac{2.303}{t}\log{}{\frac{N_{0}}{N}}$

= $\frac{2.303}{5}\log{}{10}$ = 0.4606 =  0.461 per minute