Measurements of the $^{27}{\rm Al}(\alpha,n)$ Thick Target Yield Near Threshold

TL;DR

This study provides detailed measurements of the $^{27}{ m Al}( ext{alpha},n)$ yield near threshold energies, resolving previous data discrepancies and enhancing understanding for applications in neutrino, dark matter detection, and plasma diagnostics.

Contribution

The paper offers new, precise thick-target yield measurements for $^{27}{ m Al}( ext{alpha},n)$ near threshold, addressing gaps and inconsistencies in existing data sets.

Findings

General agreement with existing data at certain energies.

Resolved discrepancies between previous data sets.

Lower yields observed below 3.5 MeV compared to prior data.

Abstract

We present results from direct measurements of the $^{27}{\rm Al}(\alpha,n)$ thick target yield from laboratory incident energies $E_{\alpha}\approx$ 3$-$5~MeV, performed with the $^{3}$HeBF$_{3}$ Giant Barrel (HeBGB) neutron detector at the Edwards Accelerator Laboratory. Our measurements have a small energy cadence in order to address discrepancies and sparseness of thick-target yield data sets existing for this energy region. We find general agreement with existing data sets, including yields derived from cross section data, while resolving a discrepancy between existing thick-target yield data sets for $E_{\alpha}\approx4-5$~MeV. However, for $E_{\alpha}<3.5$~MeV, our results are substantially lower than previous thick-target yield data and somewhat larger than yields calculated from existing cross section data. Our data complete the energy-range needed for estimates of the $^{27}{\rm Al}(\alpha,n)$ contribution to neutrino and dark matter detector backgrounds and result in increased viability of $^{27}{\rm Al}(\alpha,n)$ as a plasma diagnostic tool at fusion facilities such as the National Ignition Facility.