Unknown bump in Bragg curve 5.49 MeV alphas in dry air

Physics, Transport and Magnetic Fields
1

Dear FLUKA experts,

I’ve been simulating a simple 5.49 MeV alpha pencil beam source in a (10 x 10 x 10) cm box of air. I’m using a simple USRBIN to score the energy deposition in the box of air however I’m observing a bump in the right tail of the peak as pointed out in the Figure.

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I’m not sure as to why this is occurring and would expect a smooth decline as seen in the second Figure:

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Thanks!
test1.flair (2.1 KB)
test1.inp (1.6 KB)

4

That’s the effect of the (alpha) transport threshold. If, for the sake of accuracy, you lower the latter from the default value of 100 keV to the minimum value of 4 keV, by means of the PART-THR card, the curve smoothens as expected.

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