2H(2H,n) yield as a function of theta incorrect

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Geant4 Version: 10.7.4
Operating System: Ubuntu 22.04/CentOS 7
Compiler/Version: gcc 11.4.0/gcc 7.3.1
CMake Version: 3.22.1/3.17.5

Hello, I am trying to simulate a deuteron beam (+1 charge state) impinging on a deuterium gas filled cell, and I’m having some difficulty in getting the correct neutron yield as a function of theta. Currently, I’m getting a large amount of rear-peaked neutrons, which isn’t making much sense as this reaction shows a large forward peak and I would expect most neutrons to be there (based on diff. cross sections from https://www-nds.iaea.org/public/libraries/drosg2000/). I only care about the measuring the produced neutrons in a detector. I’m stuck with 10.7.4 because I do not control the CentOS machine and I use it to run large batch jobs.

I’m currently using a custom physics list with QGSP_BIC_All_HP and G4IonPhysicsPHP. I’ve tried different things for Hadron Elastic physics as well to no avail (HP,PHP, and LEND). No difference was observed between using the G4NDL and ENDFVIII libraries. I can provide any code snippets needed, as well as any configuration files, if that would be helpful.

I’m stumped. I’m not sure what I need to change to make this work correctly.


what is the energy of incident deuterium?

Initial 1.6 MeV. The deuterons pass through a 2.5 um HAVAR foil to reach the gas volume, nt = ~3 x 10^20 atoms/cm^2.

@jwarren , here is a case: 1.83 MeV deuterium incident 0.1 mm deuterium target with 1 g/cm3.

Maybe, this make sense.

Hi Justin.
I ran the D,d reaction on a gas target using Drosg2000 for a deuteron energy of 1.6MeV.

The reaction yield at backward angles is about 1/3 that of the forward angles, so there is a significant backward component. This also roughly agrees with data in Figure 6 page 10 of the “Handbook of Fast Neutron Generators Vol 1”, Julius Csikai. CRC Press 1987, although the incident energies there are less. The neutron energy versus angle from Drosg agrees with your general curve as expected.

I assume that your plot is from Geant4? If so, I am not clear what about it disagrees with Drosg2000. Assuming the colour scale is for yield, it is difficult to determine what is the relative difference between forward and backward angle yields.

Maybe I am missing something.