In an $\alpha$-decay,the kinetic energy of the $\alpha$-particle is $48 \, MeV$ and the $Q$-value of the reaction is $50 \, MeV$. The mass number of the mother nucleus is:

$_1H^1 + _1H^1 + _1H^2 \to X + _{+1}e^0 + \text{energy}$. The emitted particle $X$ is:

$A$ chain reaction is continuous due to

Heavy water is

Consider the nuclear fission reaction ${ }_0^1 n+{ }_{92}^{235} U \longrightarrow{ }_{56}^{144} Ba+{ }_{36}^{89} Kr+3{ }_0^1 n$. Assuming all the kinetic energy is carried away by the fast neutrons only and total binding energies of ${ }_{92}^{235} U, { }_{56}^{144} Ba$ and ${ }_{36}^{89} Kr$ to be $1800 \ MeV, 1200 \ MeV$ and $780 \ MeV$ respectively,the average kinetic energy carried by each fast neutron is (in $MeV$):

When a slow neutron goes sufficiently close to a ${U^{235}}$ nucleus,then the process that takes place is