Dear Francesco,
Thank you for clarifying the conditions.
By the way, as a quite off-topic question, as far as I know, the output unit of FLUKA
is 1/GeV/sr for USRYIELD. How did you get the output in cross section unit of (mb/MeV). Is such unit applicable for thick targets as well?
Thank you.
Not too off-topic question, actually.
I used indeed the USRYIELD scoring, not on a geometry boundary, rather at interaction level (EMERGING yield), and I asked - as recommended - for plain double differential yield. As second differential quantity, I used charge (over the unit interval from -0.5 to 0.5, which is suitable for neutrons), rather than angle (note, however, that you can always integrate over the second quantity interval and eventually get 1/GeV). Moreover, I did not perform a regular FLUKA run, but I directly simulated interactions only, and I normalized off-line with the photon reaction cross section (260 mb for the case of interest). You can mimic this by modelling a thin target and biasing the inelastic interactions with LAM-BIAS. This way you will obtain the differential yield per impinging photon, from which you can get the differential cross section by multiplying by the ratio between the reaction cross section and the interaction probability, that is
A[g/mol] / ( rho [g/cm^3] N_Av [1/mol] t )
where t is the target thickness (A the molar mass, rho the material density and N_Av the Avogadro constant).
This is not applicable to thick targets, where the projectile energy changes and its cross section too.