Question about a specific line on a gamma spectrum, here. Below is a background gamma spectrum observed by a Ge[li] detector.
I've been able to identify all the lines with mostly certainty, apart from one, highlighted, at 477 keV. I'm not sure whether I can attribute it to Be-7 as I don't understand why that would be present in the environment. I also can't see any process by which it could be being created. However, I can't find any other candidate isotopes. No other isotopes have emissions at energies which fit this spectrum.
Does anyone know of some process that might be producing Be-7? Does anyone have any other ideas?