~70 additional electrons appearing in beta decay


I am trying to generate the electron spectrum in radioactive decay, in particular regarding the isotope Se83, the decay chain is as follows

Se83 → Br83 + e + nu_e
Br83 → Kr83 + e + nu_e

The set-up is very simple, I divided the space into two regions, a sphere and a spherical shell surrounding, the isotopes are created in the center at rest; everything is made of vacuum except the black hole surrounding everything.

I used the RADDECAY card to activate the decay, and USRBDX cards (connected to a DCYSCORE card) to score the electron spectrum, you can find the input card in the attached file.

As a cross check, I scored also the total number of electrons emitted, I was expecting of seeing 2 electrons/primary, however I found ~76 electrons per primary, for which I have absolutely no physical explanation. Did I make some stupid mistake?
Everything is vacuum, so they cannot be produced by interaction with the matter…

By doing some additional checks, it seems to me that the problem is the Br83 decay: if I simulate directly that isotope, I get ~75 electrons/primary, ~74 of them have very low energy (below 30 keV), the other one has the spectrum that I would expect in a beta decay, reaching up to 1 MeV (which is the Q-value for this decay).

Does anyone knows where these electrons are coming from?

RadDecay-vacuum.inp (3.2 KB)

Hi Emilio,

Good catch!

Indeed, I can see that there are a few erroneous branching ratios in the decay products yields database used by FLUKA. The XR and Auger/CE yields are too high with respect to what data suggests and this would cause the surplus of low-energy electrons you are seeing. We have identified all 8 nuclides/isomers to be patched (among which 83m-Kr); they will be corrected for the September 4.3 release.

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