Neutron detection using far ultraviolet radiation from noble-gas excimers

When triggered in a noble gas medium at around atmospheric pressure, low-energy neutron-absorption reactions such as $^3$He(n,tp) \footnote{P. P. Hughes, {\em et al., Appl. Phys. Lett.} {\bf 97}, 234105 (2010)} and $^{10}$B(n,$\alpha$)$^7$Li \footnote{J. C. McComb, { \em et al., J. Appl. Phys. } {\bf 115}, 144504 (2014)} can generate tens of thousands of far ultraviolet photons per neutron absorbed. In some cases, up to 30\% of the $\approx$ MeV nuclear reaction energy is channeled into far ultraviolet emission. The far ultraviolet photons are produced by noble-gas excimer radiation, to which the noble gas medium is transparent, facilitating efficient optical detection. We report progress in the development of the Neutron Observatory, http://j.mp/N3utr0n , an absolute neutron detector stationed at the fundamental physics beamline at the NIST Center for Neutron Research. Our reaction initiators consist of arrays of thin films of $^{10}$B and boron-coated vitreous carbon foams \footnote{C. M. Lavelle, {\em et al., Nuc. Inst. Meth. A} {\bf 729}, 346 (2013)}