The scientific principle that forms the basis of the Tokamak technology is

Fast neutrons can easily be slowed down by

In a nuclear reactor,heavy nuclei are not used as moderators because:

Thermal neutrons are those which

What was the fissionable material used in the bomb dropped at Nagasaki (Japan) in the year $1945$?

$A$ $\gamma$-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: