Question

Why is $\mathrm{U}-235$ used in nuclear weapons?

Answer 1

Uranium:

• It is a heavy metal and it is used as a source of energy for over 50-60 years now.
• It was discovered by Martin Klaproth in the year 1789. He was a German scientist and he discovered it from a mineral called pitchblende.

Isotopes of Uranium:

There are majorly two isotopes of Uranium we have:

• Uranium-238 $\left(99.3\%\right)$ and Uranium-235 $\left(0.7\%\right)$.
• Here, Uranium-235 $\left(0.7\%\right)$ is important because when it breaks a lot of energy comes out.
• And Uranium-238 decays very slowly and it is barely radioactive.
• The nucleus of Uranium-235 is called “fissile” and Uranium-238 is called “fertile”.
• This means that U-235 on the strike of a neutron gives a tremendous amount of energy.

Critical Energy:

• It is the minimum excitation energy level above which fission could happen.

Reason why U-235 used in nuclear weapons

• The critical energy of fissile isotopes, such as U-235, is at or below the excitation of the nucleus after it has absorbed a neutron. As a result, every neutron received can trigger fission in these nuclei, and due to which fission could take place, which is again very sustainable and a lot of energy comes out.