He3 LEND Cross Sections

Hello all,

I am trying to simulate and compare the responses of He3 and BF3 neutron detectors. I’ve recently switched to using the LEND data set as, from my understanding, they provide the most accurate low energy behavior. I also utilize G4TermalNeutrons to account for low energy scattering in the materials surrounding the detectors to appropriately model their moderation prior to detection. I am currently using my own physics list (PhysicsList.cc), and I score the neutrons with G4PSEnergyDeposit and appropriate filters for the produced ions (tritons, protons, alphas, etc.).

I am seeing some interesting responses from the He3 detector where there are no captures inside the He3 gas with no tritons produced and therefore no 760 keV peak. When I switch to a reference physics list, e.g. QGSP_BIC_HP, I do see many more counts in the detectors with the appropriate capture peak at, however the total number of events is about 30% lower than some previous work has shown it should be for the geometry I am testing, which is why I switched to LEND. Additionally, when I switch to using the BF3 gas with the LEND data set I see the response as expected with the capture peaks at 2.3 and 2.7 MeV and reasonable numbers of events, so it appears the only issue is when He3 is used.

I stumbled across a post recently concerning inaccurate mass values of ions in the LEND data files (Incorrect output energy using LEND), which I fixed to get the appropriate BF3 response, and I assumed it was a similar situation in the He3. After looking through the data files however, I can’t find any other errors and all of the cross sections appear correct based off of ENDF-VII. Does anyone know if there is an issue I may be missing with the LEND data or if there is some other known discrepancies between LEND and QGSP? I am using G4 v11.0.2 and have recreated this on Mac OS as well as Ubuntu. I’d be happy to provide any other information that would be useful as well, I was just hoping to keep this concise.

Any help would be greatly appreciated!

PhysicsList.cc (4.6 KB)

Hello everybody,

I also have the exact same issue:
Until now I successfully used _HP & ThermalScattering packages to simulate 3He & BF3 counters embedded into polyethylene block getting quite good results.
Recently I wanted to compare with results produced with LEND package, but unfortunately it seems that n + 3He → p + t reaction does not occur when using LEND. I took a look inside LEND_GND1.3_ENDF.BVII.1/neutrons/002_He_003/002_He_003.000.xml database file and everything seems ok as far as I am able to understand the format. In case of BF3 counters it seems the reaction n + 10B → 7Li + alpha does occur and I get the 2 typical peaks in the BF3 counters spectrum at 2.31 MeV and 2.79 MeV although (in LEND case) I get a strange value for Q ~= 5.35 MeV.
Concerning fission: when using _HP packages I clearly see fission events and fission products, while in the case of LEND the fission does not occur.
One last remark: I searched examples in the last GEANT4.11-v11.1.1 distribution showing how to use LEND package in neutron induced reactions and I could’t find. As I understand the examples using LEND package (Hadr03, 05, 06, 07) are used only for gamma photon incident particles. Can somebody provide an example also for neutron incident?
Before starting to dig deeper in the LEND source for this issue can somebody help us with some hint or some working example?

To confirm what you are seeing,

I have a simulation that measures deposited energy in a He3 ionization chamber. It uses the QGSP_BERT_HP physics list and reproduces the chamber response to neutrons and gamma rays quite well. Notably, the thermal neutron peak at 763keV due to 3He(n,p)T is clearly seen. When I switch to the ShieldingLEND physics list, the peak is no longer present.

To confirm that LEND was not implementing the 3He(n,p)T reaction, I modified example Hadr03 to use G4HadronPhysicsShieldingLEND for Hadron Inelastic physics. The output of the unmodified version shows the 3He(n,p)T reaction for incident 25meV neutrons and protons and tritons of the appropriate energy (~572 keV and ~191 keV) for 100% of the 10^7 events. The modified version shows no such reaction, protons or tritons.

Clearly LEND does not support the 3He(n,p)T reaction, at least as implemented in ShieldingLEND.

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