Remeasurement of the $^{239}$Pu(n,f)/$^{235}$U(n,f) Cross-Section Ratio with the NIFFTE fission Time Projection Chamber Using Vapor-deposited Targets

TL;DR

This study remeasured the $^{239}$Pu(n,f)/$^{235}$U(n,f) cross-section ratio using the NIFFTE fissionTPC with vapor-deposited targets, confirming previous results and improving measurement precision across 0.1-100 MeV neutron energies.

Contribution

It introduces a remeasurement with vapor-deposited targets, enhancing accuracy and confirming prior findings within uncertainties.

Findings

Results agree with previous measurements within uncertainties.

High-precision cross-section ratio obtained across 0.1-100 MeV.

Detailed uncertainty analysis performed using 3D fission-fragment reconstruction.

Abstract

The NIFFTE fission Time Projection Chamber (fissionTPC) has been used to measure the $^{239}$Pu(n,f)/$^{235}$U(n,f) cross-section ratio for neutron-induced fission in the range of 0.1 - 100 MeV, with high precision. A white neutron source was provided by the Los Alamos Neutron Science Center, where the experiment was conducted as a remeasurement to evaluate a roughly 2% discrepancy of the previous fissionTPC results with ENDF/B-VIII.0. A detailed accounting of measurement uncertainties was performed, based on the fissionTPC's novel ability to provide three-dimensional reconstruction of fission-fragment ionization profiles. Current results obtained using a vapor-deposited, highly uniform $^{239}$Pu target, in comparison to the measurement published in 2021, where a $^{239}$Pu electroplated target was used, are presented and discussed. The remeasurement presented here is in agreement with the previous fissionTPC result within measurement uncertainties.