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Question: Answered & Verified by Expert
A radioactive nucleus of mass $M$ emits a photon of frequency $v$ and the nucleus recoils. The recoil energy will be
PhysicsNuclear PhysicsNEETNEET 2011 (Screening)
Options:
  • A $h^2 v^2 / 2 M c^2$
  • B zero
  • C $h \mathrm{~V}$
  • D $M c^2-h v$
Solution:
1586 Upvotes Verified Answer
The correct answer is: $h^2 v^2 / 2 M c^2$
Momentum of a photon
$$
p=\frac{h v}{c}
$$
Hence, Recoil energy
$$
E=\frac{p^2}{2 M}
$$
$$
\begin{aligned}
& \therefore \quad E=\frac{\left(\frac{h v}{c}\right)^2}{2 M} \\
& \text { or } \quad E=\frac{h^2 v^2}{2 M c^2} \\
&
\end{aligned}
$$

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