What is nuclear fission and nuclear fusion?

The mass of a nucleus ${ }_Z^A X$ is less than the sum of the masses of $(A-Z)$ neutrons and $Z$ protons. The energy equivalent to this mass difference is the binding energy. $A$ heavy nucleus of mass $M$ can break into two light nuclei of masses $m_1$ and $m_2$ only if $M > (m_1+m_2)$. The masses of some neutral atoms are given in the table below:

${ }_1^1 H$: $1.007825 u$	${ }_1^2 H$: $2.014102 u$	${ }_1^3 H$: $3.016050 u$	${ }_2^4 He$: $4.002603 u$
${ }_3^6 Li$: $6.015123 u$	${ }_3^7 Li$: $7.016004 u$	${ }_{30}^{70} Zn$: $69.925325 u$	${ }_{34}^{82} Se$: $81.916709 u$
${ }_{64}^{152} Gd$: $151.919803 u$	${ }_{82}^{206} Pb$: $205.974455 u$	${ }_{83}^{209} Bi$: $208.980388 u$	${ }_{84}^{210} Po$: $209.982876 u$

$1.$ The correct statement is:
$(A)$ The nucleus ${ }_3^6 Li$ can emit an alpha particle.
$(B)$ The nucleus ${ }_{84}^{210} Po$ can emit a proton.
$(C)$ Deuteron $({ }_1^2 H)$ and alpha particle $({ }_2^4 He)$ can undergo complete fusion.
$(D)$ The nuclei ${ }_{30}^{70} Zn$ and ${ }_{34}^{82} Se$ can undergo complete fusion.
$2.$ The kinetic energy (in $keV$) of the alpha particle, when the nucleus ${ }_{84}^{210} Po$ at rest undergoes alpha decay, is:
$(A)$ $5319$ $(B)$ $5422$ $(C)$ $5707$ $(D)$ $5818$

$A$ nuclear reactor generates power by fission of ${}_{92}U^{235}$ into two equal fragments of ${}_{46}Pd^{116}$ with the emission of two $\gamma$-rays of $5.2 \text{ MeV}$ each and three neutrons. The average binding energies per nucleon of ${}_{92}U^{235}$ and ${}_{46}Pd^{116}$ are $7.2 \text{ MeV}$ and $8.2 \text{ MeV}$ respectively. The usable energy released per fission event is ......... $\text{MeV}$.

The number of neutrons released when ${}_{92}^{235}U$ undergoes fission by absorbing ${}_{0}^{1}n$ and products ${}_{56}^{144}Ba$ and ${}_{36}^{89}Kr$ are formed,is:

What is a moderator? Name the material used as a moderator in a nuclear reactor.

Consider the $D-T$ reaction (deuterium-tritium fusion):
$_{1}^{2} H +_{1}^{3} H \rightarrow_{2}^{4} He + n$
$(a)$ Calculate the energy released in $MeV$ in this reaction from the data:
$m(_{1}^{2} H) = 2.014102 \; u$
$m(_{1}^{3} H) = 3.016049 \; u$
$(b)$ Consider the radius of both deuterium and tritium to be approximately $2.0 \; fm$. What is the kinetic energy needed to overcome the Coulomb repulsion between the two nuclei? To what temperature must the gas be heated to initiate the reaction?