The scored value seems not correct

[cesc (Francesc Salvat Pujol)]

Dear Xiong,

@xiongbp

Firstly, the PROD card is based on the following principle: a neutron generates secondary particles through Li (n, a)T reaction, ionizes and deposits 4.786Mev energy in ZnS (Ag) scintillator, and the number of photons generated is 1.6e+05. It is assumed that the wavelength of all photons is 450nm,
Then fraction = (1.6e + 5) * 2.756/4.786=0.0921, where E is the energy of photons, E(ev)=1240/450= 2.756, is there no problem with this calculation?

Unless I overlook something, there is a mess of units: the 4.786 are in MeV, whereas the 2.756 should be eV, so there appears to be a factor 1000 dancing (which probably cancels out with a missing number of primaries, 1000 in your case, and you get the a consistent result in an accidental way).

One check you can do is to write down the following quantities (pick values up from the *001.out fie):

• Energy deposited per primary (Edep)
• Fraction of deposited energy that goes into optical fotons (fr)
• Total (unweighted!) number of optical photons generated (Noph). Note that this is indeed an absolute number, not divided per primary.
• Number of primaries (Nprim).
• The optical photon energy (Egamma), which in your case is unique.

You could then check that Noph = Edep * Nprim * fr / Egamma

NB: this quick check works because you have a single optical photon frequency.

@xiongbp

In USRBDX, the output is set to < x > * y, X Norm is set to 1/ev, and X and Y do not set log. Why does the number of photons displayed on the output Y axis exceed 1.6e + 5, about 4e+05?

(The primary energy is not of terrible concern to answer the question, but do note that in the post above you claimed 10 MeV energy, which turned out to be 1 MeV, and now we have ~thermal energies instead… just make sure you run with you intend to run.)

The point of displaying quantities as <x> * y is to have a faithful representation of the considered spectrum in a (at least horizontal) log scale, as carefully elaborated upon in this post: Understanding USR-1D plot - #11 by xiongbp

Selecting <x> you de facto request a proper treatment of the Jacobian for going from linear to log horizontal scale. If you plot <x>*y in a linear horizontal scale, this defeats the purpose. I now fail to see how one could extract quantitative info from such a representation.

Also, note that your USRBDX looks at whatever optical photons go from region MIXTURE (which is just the very first segment of your target!) to region BLANK. You may want to revise this.

@xiongbp

In order to simulate the detection efficiency, I want to get the calculation results under multiple incident neutrons instead of per primary. How should I set it?

You’d simply need to scale your Monte Carlo results (given per primary) by the intensity of the neutron beam (all you need to know is how many neutrons impinge on your sample to scale the results accordingly).

With kind regards,

Cesc