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

In the proton-proton cycle in the Sun,the energy released when an electron and its antiparticle combine is $\qquad$ .

Slowing down of neutrons: In a nuclear reactor,a neutron of high speed (typically $10^{7} \; m s^{-1}$) must be slowed to $10^{3} \; m s^{-1}$ so that it can have a high probability of interacting with isotope $^{235}_{92}U$ and causing it to fission. Show that a neutron can lose most of its kinetic energy in an elastic collision with a light nucleus like deuterium or carbon,which has a mass of only a few times the neutron mass. The material making up the light nuclei,usually heavy water $(D_{2}O)$ or graphite,is called a moderator.

The binding energy per nucleon of ${}_3^7Li$ and ${}_2^4He$ nuclei are $5.60 \, MeV$ and $7.06 \, MeV$, respectively. In the nuclear reaction ${}_3^7Li + {}_1^1H \to 2 \, {}_2^4He + Q$, the value of energy $Q$ released is ............ $MeV$.

$A$ star initially has $10^{40}$ deuterons. It produces energy via the processes:
$_1H^2 + _1H^2 \to _1H^3 + p$
$_1H^2 + _1H^3 \to _2He^4 + n$
The masses of the nuclei are as follows:
$M(H^2) = 2.014 \, amu; \, M(p) = 1.007 \, amu;$
$M(n) = 1.008 \, amu; \, M(He^4) = 4.001 \, amu$
If the average power radiated by the star is $10^{16} \, W$, the deuteron supply of the star is exhausted in a time of the order of:

When two deuteron nuclei fuse to form a helium nucleus,energy is released because the mass of the helium nucleus is .....