Can stimulated emission happen in nuclear energy states? We know that stimulated emission of photons can occur when photons induce an electron in a metastable state to drop down, creating a new photon which is identical to the original photon in terms of frequency, phase, and polarization.
I'm wondering, can the phenomenon of stimulated emission be extended to nuclear transitions as well? The existence of nuclear stimulated emission could mean that gamma ray lasers are possible.
 A: It seems that research has reached the stage of creating a gamma ray laser, a proposal:

In the study, which is published in a recent issue of Physical Review Letters, Tkalya explains that a nuclear gamma-ray laser has to overcome at least two basic problems: accumulating a large amount of isomeric nuclei (nuclei in a long-lived excited state) and narrowing down the gamma-ray emission line. The new proposal fulfills these requirements by taking advantage of thorium’s unique nuclear structure, which enables some of the photons from an external laser to interact directly with thorium’s nuclei rather than its electrons.

This involves nuclear transitions , but the output is electromagnetic .
If you mean whether  a proton, or alpha , laser is possible , i.e. incoming protons stimulating emission on an isotope with the same energy level protons  , this involves the strong interactions and electromagnetism and I would think it very hard to achieve even if there exist long lived isotopes .
Neutrons are difficult to control but this might interest you.
