Question

A radioactive nucleus decays by two different processes. The half life for the first process is $10 s$ and that for the second is $100 s$. the effective half life of the nucleus is close to:

• A. 9 sec
• B. 55 sec
• C. 6 sec
• D. 12 sec

Answer 1

Answer: (A)

9 sec

Answer 2

$\frac{1}{ T _{ eff }}=\frac{1}{ T _{1}}+\frac{1}{ T _{2}}$
$T _{ eff }=\frac{ T _{1} T _{2}}{ T _{1}+ T _{2}}$
$=\frac{1000}{110}=\frac{100}{11}=9.09$
$T _{ eff } \cong 9$