Efficient conversion of $^{3}$He($n$,\textit{tp}) and $^{10}$B($n$,\textit{$\alpha $}$^{7}$Li) reaction energies into far-ultraviolet radiation by noble gas excimers

Previous work$^{1,2 }$showed that the $^{3}$He($n$,\textit{tp}) reaction in a cell of $^{3}$He at atmospheric pressure generated tens of far-ultraviolet (FUV) photons per reacted neutron. Here we report amplification of that signal by factors of 1000 when noble gases are added to the cell. Calibrated filter-detector measurements show that this large signal is due to noble-gas excimer emissions, and that the nuclear reaction energy is converted to FUV radiation with efficiencies of up to 30{\%}. Our results have been placed on an absolute scale through calibrations at the NIST SURF III Synchrotron and Center for Neutron Research.$^{3}$ We have also seen large neutron-induced FUV signals when the $^{3}$He gas in our system is replaced with a $^{10}$B film target; an experiment on substituting $^{3}$He with BF$_{3}$ is underway. Our results suggest possibilities for high-efficiency, non-$^{3}$He neutron detectors as an alternative to existing proportional counters. $^{1}$A. K. Thompson, \textit{et al., J. Res. Natl. Inst. Stand. Technol.} \underline {\textbf{113}}\underline {, 69} (2008) $^{2}$M. A. Coplan, A. K. Thompson and C. W. Clark, \underline {U.S. Patent No. 7,791,045} (2010) $^{3}$P.P. Hughes, \textit{et al.,} \underline {arXiv:1009.4707} (\textit{Appl. Phys. Lett. }in press, 2010)