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 the Triton nucleus.

Hint: The transformation requires energy.

Explanation: Tritium \(\rightarrow{ }_1 \mathrm H^3.\) The nucleus contains \(1\) proton and \(2\) neutrons. If one neutron decays \(n \rightarrow p+e^{-}+\bar{v},\) the nucleus may have \(2\) protons and one neutron, i.e., tritium will transform into \({ }_2 \mathrm{He}^3\) (with 2 protons and one neutron). But this does not happen because triton energy is less than that of \({ }_2 \mathrm{He}^3\) nucleus, i.e., transformation is not allowed energetically.
Hence, option (1) is the correct answer.

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