Ncert Exercises & Solutions

Tritium is an isotope of hydrogen whose nucleus triton contains \(2\) neutrons and \(1\) proton. Free neutrons decay into\(p+e^{-1}+\nu^{-1}.\) If one of the neutrons in Triton decays, it would transform into \(\mathrm{He}^{3}\) nucleus. This does not happen. This is because:

1.	triton energy is less than that of a \(\mathrm{He}^{3}\)nucleus.
2.	the electron created in the beta decay process cannot remain in the nucleus.
3.	both the neutrons in Triton have to decay simultaneously resulting in a nucleus with \(3\) protons, which is not a \(\mathrm{He}^{3}\)nucleus.
4.	free neutrons decay due to external perturbations which is absent in Triton nucleus.

(1) Hint: The transformation requires energy.

Step 1: Find the change in energy in the transformation.

Tritium (₁He³) contains 1 proton and 2 neutrons. A neutron decays as

n \to p + \bar{e} + \bar{ν}

, the nucleus may have 2 protons and one neutron, i.e., tritium will transform into

{}_{2}{He}_{3}

(2 protons and 1 neutron)

Triton energy is less than that of

{}_{2}{He}_{3}

nucleus, i.e., transformation is not allowed energetically.

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