Limitations on the Photo-disintegration Process as a Source of VHE Photons

We consider whether photo-disintegration is ever able to provide an effective mechanism for the production of VHE $\gamma$-ray emission from astrophysical sources. We find that the efficiency of this process is always smaller by a factor $A/Z^{2}$ ($\sim 4/A$) than that of nuclei cooling through Bethe-Heitler pair-production. Furthermore, for sources optically thin to TeV emission, we find that the efficiency of this process can be no more than $3\times 10^{-5}(R_{\rm source}/R_{\rm Larmor})$, where $R_{\rm source}$ is the source size and $R_{\rm Larmor}$ is the CR nuclei Larmor radius. We conclude that this process is unable to provide an effective mechanism for VHE $\gamma$-ray emission from astrophysical sources.