# How in Cesium 137 spectroscopy Barium X-rays being detected?

Iv been looking at gamma ray spectroscopy of late for a project that I am currently researching and going to be doing in the lab, but what I cannot seem to figure is how the barium x-rays are being shown in the spectrum?

Looking at the decay scheme and comparing it to a c137 spectrograph I cant see how the x-ray photons are being generated. My only reasoning is that there is some sort of characteristic x-ray being formed from during the transition gamma photo being ejected during the decay.

• Look at your energy level diagram - 94.6% of the decays go to the excited level of the Barium nucleus. This excited level then decays by emission of the 662keV gamma. That gamma has more than enough energy to knock out an electron from a Ba atom, leading to characteristic x-rays. Why do you not think that is possible? – Jon Custer Oct 9 '18 at 21:27
• @BenCrowell I did not realize that internal conversion was the same as what Jon described, so I learned something and removed my comments. – Pieter Oct 10 '18 at 7:12

Beta decay changes $$Z$$ which may produce a hole in the K shell ("shake-up"). That hole then decays. But that is then the K-shell of the progeny nucleus: barium.
Edit: probably more important: the metastable state of $$^{137}$$Ba decays by internal conversion in which a K electron was emitted.
• @BenCrowell Skake-up: a sudden change in $Z$ projects the $1s$ orbitals on a slightly different potential. Overlap is not perfect. – Pieter Oct 10 '18 at 0:21
• I see. Sorry, in earlier comments I was thinking "electron conversion" when you wrote "internal conversion." This seems like the most likely of the reasons we've discussed, since it explains why K is preferred. The order of magnitude of the probability of x-ray emission seems about right for this process as well; internal conversion is most probable for low-energy gamma decay, and this one is a fairly high energy, so it makes sense that the probability appears to be $<\sim 0.1$. – user4552 Oct 10 '18 at 0:31