The rest mass of an electron as well as that of a positron is $0.51 \, MeV$. When an electron and a positron annihilate, they produce gamma-rays of wavelength(s):

$A$ nucleus with mass number $220$ initially at rest emits an $\alpha -$ particle. If the $Q$ value of the reaction is $7.8 \, MeV$ and subsequently after the emission of the $\alpha -$ particle,a photon of energy $1.2 \, MeV$ is also emitted. The kinetic energy of the $\alpha -$ particle is ? .......... $MeV$

Nuclear fusion is common to the pair:

The average number of prompt neutrons produced per fission of ${U^{235}}$ is

$_{1}^{2} H + _{1}^{3} H \to _{2}^{4} He + _{0}^{1} n$
If the binding energies of $_{1}^{2} H, _{1}^{3} H$ and $_{2}^{4} He$ are $a, b$ and $c$ (in $MeV$) respectively, then the energy released in the reaction is:

The energy released when $\frac{7}{17.13} \text{ kg}$ of $^7_3\text{Li}$ is converted into $^4_2\text{He}$ by proton bombardment is $\alpha \times 10^{32} \text{ eV}$. The value of $\alpha$ is . . . . . . . (Nearest integer) (Mass of $^7_3\text{Li} = 7.0183 \text{ u}$,mass of $^4_2\text{He} = 4.004 \text{ u}$,mass of proton $= 1.008 \text{ u}$,$1 \text{ u} = 931 \text{ MeV/c}^2$,and Avogadro number $N_A = 6.0 \times 10^{23} \text{ mol}^{-1}$)