Space to Air High-Altitude Region Adjoint Neutron Transport
Abstract
The goal of this work was to use the adjoint transport equation to characterize the energy spectrum of a neutron source located in the upper atmosphere using the time-energy fluence at the satellite. This adjoint approach directly solves for the source spectrum thereby potentially enabling device reconstruct ion. The adjoint method also could improve computational efficiency over the forward method. The adjoint transport equation was solved via Monte Carlo methods in a new program called SAHARA written in Python 3.7. A new adjoint source event estimator was developed to improve the computational efficiency. This work explores SAHARA's development, and its performance for mono-energetic and continuous energy sources. In general, the identified source spectra were shifted towards lower energies approximately five percent, but were able to capture the source spectrum shapes. Additionally, continuous energy sources still passed a 2-D Kolmogorov-Smirnov (K -S) test. Lastly, SAHARA was applied to the real-world neutron energy spectra of Fat Man and Little Boy. Although these spectra were also noticeably shifted towards lower energies, the spectral features are still recognizable and the spectra passed a 2-D K-S test. SAHARA provides a new tool for estimating the source spectrum from space- based neutron measurements.
Document Details
- Document Type
- Technical Report
- Publication Date
- Mar 01, 2021
- Accession Number
- AD1145714
Entities
People
- Zachary W. Lamere
Organizations
- Air Force Institute of Technology