Error -" Oepsmp-> sampling gave unphysical tail:......."

Dear Fluka Users
I am trying this simulation which is pretty simple- estimate the thickness of lead needed to attenuate gamma rays.
The problem is that I am getting series of errors of following type-
" Oepsmp-> sampling gave unphysical tail: Z= 1 shell= 1 Function= 3
Oepsmp: p_sampled/(alpha x elmass)= 11.216752185731263 p_max/(alpha x elmass)= 10.699999999999999 ".
There doesnt seem to be any error in the geometry. Source routine seems OK too. The particles are transported alright (I think!). can someone please let me know whats happening?
The input file, error file and the source routine areattached. gammatest.inp (9.9 KB) gammatest_01001.err (25.8 KB) source1.f (8.8 KB) spectrum1.dat (68 Bytes)

Dear Saurabh,

These warning messages can be safely ignored: they indicate that on rare occasions (6 in your 6E7 primary-particles run → once every 1E7 photons) a too large electron “momentum” was sampled during a Compton scattering event.

To be a bit more explicit, see the following reference, where the Compton scattering model implemented in FLUKA is described in a bit more detail:

You’ll see that the Compton profile is fitted with Eq 2.14, consisting of a Fermi-Dirac distribution, two Gaussians, and two exponentials. The warning you witness may appear once in a blue moon, allegedly when sampling the tail of the exponentials (excessively high electron “momentum”). Under such situations the attempt is rejected and resampled, so this is not an issue.

I understand your run did not crash; let me know if I misunderstood.



1 Like

Dear Cesc
thanks. No, the run did not crash and it was OK. Thanks also for suggesting the reference.