Neutron Detection by Noble Gas Excimer Scintillation

Abstract

The field of neutron detection has many essential applications, from nuclear reactor instrumentation, oil-well logging, radiation safety, and, in recent years, homeland security. Due to the shortage and increasing cost of the neutron absorber used in most conventional gas-filled proportional counters, there has been an increased motivation for the development of alternative methods of neutron detection that do not rely on <super>3</super>He. Excimer-based neutron detection (END) is a potential alternative with many advantages, notably the lack of dependence on <super>3</super>He. Similar to traditional proportional counters, END operates on the interaction of a neutron with a neutron absorbing nucleus (<super>10</super>B, <super>6</super>Li, or <super>3</super>He). The energetic charged particles produced in these reactions lose energy in the surrounding gas background and cause ionization and excitation of the noble gas molecules. The difference between END and traditional gas-filled detectors, which collect the ionized charge to produce a detectable signal, is the formation of noble gas excimers (Ar₂<super>*</super>, Kr₂<super>*</super>, or Xe₂<super>*</super>). These excited dimers decay from an excited state back to ground level and emit far-ultraviolet (FUV) radiation in the form of photons which can be collected using a photomultiplier tube (PMT) or other photon detector. The most important advantage to these potential detectors is the fact that they do not rely on the use of <super>3</super>He.

The excimer scintillation yield from rare noble gases following the <super>10</super>B neutron capture reaction in both <super>10</super>B enriched BF₃ gas and reticulated vitreous carbon foam (RVC) coated with a layer of B₄C is the focus of this thesis. Experimental data were collected at the National Institute of Standards and Technology (NIST) and on a recently established thermal neutron beamline at the Maryland University Training Reactor (MUTR). The comparison of these data to data from previous thin-film experiments provides the groundwork for the continuation of future END work using these materials, which will be used to develop and optimize a deployable neutron detector based on excimer emission.