$A$ $\gamma$-ray photon creates an electron-positron pair. If the rest mass energy of an electron is $0.51 \, MeV$ and the total kinetic energy of the electron-positron pair is $0.78 \, MeV$,then the energy of the $\gamma$-ray photon in $MeV$ is:

One of the fusion reactions in the sun is given by ${ }_{1}^{2} H+{ }_{1}^{1} H \rightarrow{ }_{2}^{3} He+\gamma+Q$. Calculate the energy $Q$ released in the reaction. (in $MeV$)

$A$ nuclear fuel rod generates energy at a rate of $5 \times 10^8 \,W/m^3$. It is in the shape of a cylinder of radius $4.0 \,mm$ and length $0.20 \,m$. $A$ coolant of specific heat $4 \times 10^3 \,J \cdot kg^{-1} \cdot K^{-1}$ flows past it at a rate of $0.2 \,kg/s$. The temperature rise in this coolant is approximately ............ $^{\circ}C$.

The binding energy per nucleon for deuteron $(_1H^2)$ and helium $(_2He^4)$ are $1.1 \, MeV$ and $7 \, MeV$ respectively. When two deuterons fuse to form a helium nucleus,the energy released is ........... $MeV$.

Complete the reaction: $n + _{92}^{235}U \to _{56}^{144}Ba + .... + 3n$

When a $_4Be^9$ atom is bombarded with $\alpha$-particles,one of the products of nuclear transmutation is $_6C^{12}$. The other product is: