AmBe / PuBe source-term simulation

The centrepiece of my PhD. Instead of simulating $^{241}$Am $\alpha$ decay interacting with $^{9}$Be through a Geant4 physics list, this simulation uses the measured differential cross sections of the $^{9}$Be($\alpha$,n)$^{12}$C reaction to generate neutrons and $^{12}$C ions directly in the PrimaryGenerator class.

Produces Doppler-broadened 4.4 MeV and 3.2 MeV $\gamma$ rays from $^{12}$C de-excitation, so the excited-state ratio per neutron can be verified.
Each stage is validated against accepted data, including the $^{241}$Am spontaneous-fission fragment mass distribution and the emergent neutron spectrum.
Includes a (less extensively verified) $^{239}$PuBe implementation, and the source term plus a simulation template are released publicly with the paper.

Published as (Falezza et al., 2025).

References

2025

NIM A
Simulation and analysis of an AmBe source

Filippo Falezza, Jack Bishop, Tzany Kokalova, and 4 more authors

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2025

Abs DOI Bib

This article details a comprehensive Geant4 simulation based on an analytical approach to the PrimaryGenerator class. Rather than simulating the interaction of 241Am alpha decay with 9Be through the in-built Geant4 physics list, this simulation uses the differential cross sections of the 9Be(alpha,n)12C reaction to directly produce neutrons and 12C ions while simultaneously increasing computational efficiency. The advantage of this is the ability to generate Doppler broadened 4.4 MeV and 3.2 MeV gamma rays from 12C decay and hence the verification of the excited states ratio per neutron emission. Each stage of the simulation has been verified against commonly accepted results, including the mass distribution of the 241Am fission fragments. The features of the emerging neutron spectrum have been compared to commonly accepted data, confirming the validity of the simulation. The source term and the simulation template are made publicly available in conjunction with this article. Although not extensively verified, the 239PuBe neutron source has also been implemented, making it a straightforward framework for implementing further sources.
@article{Falezza2025_AmBe, title = {Simulation and analysis of an AmBe source}, author = {Falezza, Filippo and Bishop, Jack and Kokalova, Tzany and Wheldon, Carl and Pirrie, Stuart and Conroy, Max and Curtis, Neil}, journal = {Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment}, volume = {1085}, pages = {171233}, year = {2025}, issn = {0168-9002}, doi = {10.1016/j.nima.2025.171233}, url = {https://www.sciencedirect.com/science/article/pii/S0168900225010356}, keywords = {AmBe, Neutron, Source, Geant4, Source term, Analytical, Fission, Monte Carlo, Alpha-induced, Generator}, dimensions = {true}, }