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Question about a specific line on a gamma spectrum, here. Below is a background gamma spectrum observed by a Ge[li] detector.

spectrum

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?

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    $\begingroup$ Did you have a look at nucleardata.nuclear.lu.se/database/nudat ? There, you get a large tables of isotopes emitting 477keV: nucleardata.nuclear.lu.se/Scripts/database/nudat/… . However, you have to check which isotopes are reasonable, most seem to be a bit exotic. (Also, I wonder why Be7 is not listed...) $\endgroup$
    – sweber
    Commented Aug 27, 2015 at 8:57
  • $\begingroup$ Very close, I use this one: nucleardata.nuclear.lu.se/toi/… As it was more regularly updated. You can find Be-7 there. $\endgroup$
    – Matt
    Commented Aug 27, 2015 at 9:20
  • $\begingroup$ Beyrillium-7 is pretty exotic and can be made in cosmogenic processes, but the rate is tiny (events per square-cm per year...). It worth taking the lines you are confident that you have identified and checking the energy calibration of the device. My experience suggests that a fairly modest miscalibration in energy can lead to unnecessary struggles in identifying lines. $\endgroup$
    – dmckee --- ex-moderator kitten
    Commented Aug 27, 2015 at 14:32

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Be-7 is common atmospheric radionuclide produced by cosmic ray spallation of nitrogen and oxygen. Ground level concentration of Be-7 is in order of ~mBq per cubic meter of air. Main deposition process of Be-7 is a wet scavenging which yields to ~Bq per litre of rainwater. It is therefore possible to find Be-7 in background (depends on location of measurement, obviously).

You could also check the spectrum for 1275 keV line coming from Na-22, which has the same cosmogenic origin as Be-7.

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