Question: Q. 3. Tritium is an isotope of hydrogen whose nucleus Triton contains 2 neutrons and 1 proton. Free neutrons decay into $p+\bar{e}+v$. If one of the neutrons in Triton decays, it would transform into ${ }_{2} \mathrm{He}^{3}$ nucleus. This does not happen. This is because
(a) triton energy is less than that of a $\mathrm{He}^{3}$ nucleus.
(b) the electron created in the beta decay process cannot remain in the nucleus.
(c) both the neutrons in triton have to decay simultaneously resulting in a nucleus with 3 protons, which is not a $\mathrm{He}^{3}$ nucleus.
(d) because free neutrons decay due to external perturbations which is absent in a triton nucleus.
[NCERT Exemplar]
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Solution:
Ans. Correct option : (a)
Explanation: Triton $\left({ }_{1}^{3} \mathrm{H}\right)$ has 1 proton and 2 neutrons.
If a neutron decays as,
$$ n \rightarrow p+\bar{e}+v $$
Then nucleus will have 2 protons and 1 neutron, i.e. triton atom converts in ${ }{2} \mathrm{He}^{3}$ ( 2 proton and 1 neutron). Binding energy of ${ }{1} \mathrm{H}^{3}$ is much smaller than ${ }_{2} \mathrm{He}^{3}$ so transformation is not possible energetically.
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