According to activity law R=R0e−λt...........(i) where R0= initial activity at t=0 R=activity at time t λ=decay constant According to given problem R0=N0 couts per minute R=
N0
e
counts per minute t=5 minutes Substituting these values in equation (i), we get
N0
e
=N0e−5λ e−1=e−5λ 5λ=1 or λ=
1
5
per minute At t=T
1
2
the activity R reduces to
R0
2
where T
1
2
= half life of a radioactive sample From equation (i), we get
R0
2
=R0e−λT
1
2
eλT
1
2
=2 Taking natural logarithms on both sides of above equation,we get λT
