Question

Which one of the following is fissionable?

${}_{92}{}^{235}Uor{}_{92}{}^{238}U$.

Answer 1

A nuclear reaction in which a heavier nucleus is split into lighter nuclei with a simultaneous release of a large amount of energy is called nuclear fission reaction.

For example, the fission of uranium-235 nucleus is written as:

${}_{92}{}^{235}\mathrm{U}+{}_0{}^1\mathrm{n}\to {}_{56}{}^{139}\mathrm{Ba}+{}_{36}{}^{94}\mathrm{Kr}+3{}_0{}^1\mathrm{n}+\mathrm{Energy}$

U-235 is fissionable because it can split into smaller molecules when a lower energy neutron[slow neutron] is fired at it but in U-238, it undergoes nuclear fission but the neutrons fired at it would need more energy[fast neutron] in order for fission to take place.

Thus, ${}_{92}{}^{235}U$ is fissionable.