COMEDK Exam 2013 Solved Paper

In radioactive decay, the decay rate is proportional to the amount of substance. So, for change of count rate from 240 per min to 30 per min, let N be the number of half-life passed in one hour. Then,

240

2N

=30
⇒2N=8
⇒N=3
Half - life, t

1

2

=

1h

3

=

60

3

min=20min