Fast neutrons can be easily slowed down by:

Suppose we think of the fission of a $^{56}_{26} Fe$ nucleus into two equal fragments,$^{28}_{13} Al$. Is the fission energetically possible? Argue by working out the $Q$-value of the process.
Given: $m(^{56}_{26} Fe) = 55.93494 \; u$ and $m(^{28}_{13} Al) = 27.98191 \; u$.

Assertion: Energy is released when heavy nuclei undergo fission or light nuclei undergo fusion.
Reason: For heavy nuclei,binding energy per nucleon increases with increasing $Z$,while for light nuclei,it decreases with increasing $Z$.

Nuclear fission is best explained by
[$AIPMT$ $2000$]

Nuclear fusion is common to the pair:

$A$ $^{235}U$ nuclear reactor generates energy at a rate of $3.70 \times 10^7 \text{ J/s}$. Each fission liberates $185 \text{ MeV}$ of useful energy. If the reactor has to operate for $144 \times 10^4 \text{ s}$, the mass of the fuel needed is (Assume Avogadro's number $= 6 \times 10^{23} \text{ mol}^{-1}$, $1 \text{ eV} = 1.6 \times 10^{-19} \text{ J}$) (in $\text{ kg}$)