The operation of a nuclear reactor is said to be critical when the value of the neutron multiplication factor $K$ is:

The energy of the fast neutrons emitted in a nuclear fission reactor is approximately $\qquad$ .

Which of the following is a fusion reaction?

The process that mainly takes place in stars to produce energy is:

$A$ $\gamma$-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:

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