Separate the inelastic and capture reactions in a tally

[Alexander Camargo]

Hello everyone. I have a 14 MeV neutron source and a gamma photon detector at a distance. This detector is for counting photons from inelastic reactions and capture.
How do I configure a tally to output only inelastic and capture reactions separately?

 

[Alex A]

Do you need a count, or do you need an energy spectrum?

Edit, these might be solved the same way - with an fm card. Say you used an f4 tally with the detector containing material 3. Then,
fm4 -1 3 102
Would modify the tally to produce the result for (n,gamma) capture events.
Where,
fm4 -1 3 2
Would modify the tally to produce the result for elastic scattering events.
102 being the ENDF/B capture reaction type and 2 being the elastic cross section reaction type.

 

[Alexander Camargo]

Do you need a count, or do you need an energy spectrum?

Edit, these might be solved the same way - with an fm card. Say you used an f4 tally with the detector containing material 3. Then,
fm4 -1 3 102
Would modify the tally to produce the result for (n,gamma) capture events.
Where,
fm4 -1 3 2
Would modify the tally to produce the result for elastic scattering events.
102 being the ENDF/B capture reaction type and 2 being the elastic cross section reaction type.

Got it. I'm using tally F4. My intention is to calculate the sigma of a given material. I need to separate only the part of the spectrum that comes from capture reactions. In this case, the detector isn't the target material; I need to calculate the material that interacts with the beam, and only then will the detector calculate it. I'll try it out. Thank you very much.

 

[Alexander Camargo]

Do you need a count, or do you need an energy spectrum?

Edit, these might be solved the same way - with an fm card. Say you used an f4 tally with the detector containing material 3. Then,
fm4 -1 3 102
Would modify the tally to produce the result for (n,gamma) capture events.
Where,
fm4 -1 3 2
Would modify the tally to produce the result for elastic scattering events.
102 being the ENDF/B capture reaction type and 2 being the elastic cross section reaction type.

I don't think the reaction number is 102. I simulated it and got this error: "fatal error. Illegal photon reaction number, 102, on FM 24 card."
Is there a reference to where I can find this table?

 

[Alex A]

Oh, is the detector a gamma detector? Not a neutron detector?
You want photoelectric events and Compton events?
Or was the tally supposed to be a neutron tally?

 

[Alexander Camargo]

Ah, o detector é um detector gama? Não é um detector de nêutrons?
Você quer eventos fotoelétricos e eventos Compton?
Ou a contagem deveria ser uma contagem de nêutrons?

When a neutron source interacts with any material, there are reactions that produce photons, namely photons from inelastic reactions and photons from capture reactions. I am counting these photons, I just wanted to separate the capture and inelastic ones into different tallies. To calculate the sigma of a material, I only need the photons from capture reactions; with this, I can calculate the sigma of this material.

 

[Astronuc]

I can calculate the sigma of this material.

Based on the detector (gamma ray spectrometer?) response?

When a neutron source interacts with any material, there are reactions that produce photons, namely photons from inelastic reactions and photons from capture reactions.

True. A neutron scattering off a nucleus (of mass A) may excite an internal state from which a characteristic photon is emitted; the neutron loses some energy to the nuclear excitation and some to the exchange of energy/momentum in the collision by which the nucleus is displaced/recoiled. The neutron with less energy is scattered; high energy neutrons tend to scatter forward (small angle neutron scattering (SANS)). The gamma emissions are characteristic of nucleus of atomic number Z and mass A.

One might also encounter a (n,n') reaction in which the neutron is absorbed and then another neutron is emitted.

https://en.wikipedia.org/wiki/Small-angle_neutron_scattering
https://www.ncnr.nist.gov/programs/sans/pdf/sans_theory.pdf

https://en.wikipedia.org/wiki/Neutron_scattering#Inelastic_neutron_scattering
https://neutrons.ornl.gov/sites/default/files/intro_to_neutron_scattering.pdf
https://www.ncnr.nist.gov/summerschool/ss09/pdf/Lecture_6_Inelastic.pdf
https://www.ansto.gov.au/sites/default/files/news-documents/acs018530.pdf
https://www.oxfordneutronschool.org/2024/Lectures/Garcia Sakai - INS.pdf

The displaced atom will likely be ionized and/or excited, so it would produce some X-rays

Regarding capture, if photons are produced from the reaction, that is known as radiative capture, but unlike inelastic scattering, the internal nuclear energy levels of the excited nucleus are different from the original atom (the difference attributed to A+1(after capture) to A (before capture), with Z unchanged. However, one might obtain a 'spallation' reaction in which proton, deuteron or other nuclear fragment, e.g., alpha particle, are emitted, with some gammas and X-rays involved as well. If a proton is ejected upon neutron capture, then Z decreases by 1 to Z-1, but A remains the approximately the same. Any photons emitted would be different for the Z-1 nucleus than the Z nucleus.

If one is using Monte Carlo code, e.g., MCNP or OpenMC, one is inputting microscopic cross-section(s) from a library, e.g., ENDF/B, so a simulation might help one confirm a set of cross-sections through comparing detector results with those of the simulation calcuations.

I am more familiar with neutron radiography and activation than scattering analysis techniques, but I am working toward the latter.