NeSST: A Python Tool for Neutron Spectra and Synthetic Diagnostics in Inertial Confinement Fusion

TL;DR

NeSST is an open-source Python tool that rapidly generates and analyzes neutron spectra from inertial confinement fusion implosions, incorporating scattering effects, asymmetries, and detector response modeling.

Contribution

NeSST introduces a comprehensive, flexible Python package for neutron spectrum simulation and diagnostics in ICF, integrating nuclear data, scattering physics, and detector modeling.

Findings

Efficiently computes primary and scattered neutron spectra from ICF implosions.

Incorporates areal density asymmetries and ion velocity effects into spectral analysis.

Includes a full forward model for detector signal prediction with configurable instrument response.

Abstract

We present the Neutron Scattered Spectra Tool (NeSST), an open-source Python package for rapidly constructing primary and singly scattered neutron spectra from inertial confinement fusion (ICF) implosions. NeSST evaluates primary spectra for deuterium-tritium (DT), deuterium-deuterium (DD) and tritium-tritium (TT) reactions. Differential and total nuclear cross sections are read directly from Evaluated Nuclear Data File (ENDF) libraries. This enables elastic ($n$D, $n$T) and inelastic [D$(n,2n)$p, T$(n,2n)$D] scattering from DT fuel, as well as scattering from additional ablator materials such as $^{12}$C, to be treated within a common framework. Relativistic corrections to elastic scattering kinematics are included. Areal density asymmetries are incorporated through a Legendre mode expansion of the neutron-averaged projected areal density, allowing the spectral signatures of implosion non-uniformities to be computed and fitted. The effect of scattering ion velocities on the neutron backscatter edge shape is handled through pre-computed ion-velocity-dependent scattering kernels. A synthetic neutron time-of-flight (nToF) module converts energy spectra into detector signals with a full forward model that includes configurable instrument response functions (IRFs), energy-dependent scintillator sensitivity, and beamline attenuation. The code is publicly available at https://github.com/aidancrilly/NeSST