Reason for difficulty in detecting presence of antineutrino during $\mathit{\beta }$ decay
Define decay constant of radioactive nucleus
Derive expression for mean life in terms of decay constant
● Penetrating power is high
● Do not interact with matter (weak interaction) (any one)
● Decay constant is the reciprocal of the time duration in which undecayed radioactive nuclei reduce to $1∕\mathrm{e}$ times the nuclei present initially.

$\mathit{\tau }=\frac{\underset{0}{\overset{\mathit{\infty }}{\int }}\mathit{t}\mathit{d}\mathit{N}}{{\mathit{N}}_0}$
$\mathit{\tau }=\frac{\underset{0}{\overset{\mathit{\infty }}{\int }}\mathit{t}\left({\mathit{N}}_0\mathit{\lambda }{\mathit{\epsilon }}^{-\mathit{\lambda }\mathit{t}}\mathrm{dt}\right)}{{\mathit{N}}_0}=\mathit{\lambda }\int \mathit{t}{\mathit{e}}^{-\mathit{\lambda }\mathit{t}}\mathrm{dt}$
$\mathit{\tau }=\frac{1}{\mathit{\lambda }}$
OR
(a) Stating distinguishing feature of nuclear force.
(b) Drawing a plot showing variation of potential energy.
(c) Marking the regions.
(1) Short rang force
(2) Strongest force
(3) Attractive in nature
(4) Does not depend on charge (any two)
(b) : repulsive force
$\mathit{r}>{\mathit{r}}_0:$ attractive force