Characterizing a new scintillator detector array for neutron spectroscopy with spectrum unfolding

Neutron spectroscopy plays an important role in many areas of physics research, including astrophysics, nuclear structure, and nuclear non-proliferation. In non-proliferation, it allows for nondestructive assay (NDA) measurements, as neutrons can easily escape the sample material. Comparing this neutron spectrum with spectra of known reactions can help determine the makeup of the sample. However, due to their lack of charge, neutrons are inherently difficult to detect. The traditional method of neutron spectroscopy, time of flight (TOF), involves the time it takes each neutron to cross a known distance. There are several drawbacks to this method: firstly, an initial timing signal is not always available, as is the case with NDA. Also, the energy resolution for TOF depends on detector distance, but an increased distance leads to poor measurement statistics. Spectrum unfolding is a novel method of neutron spectroscopy that eliminates these issues. By utilizing TOF to carefully characterize the relationship between neutron energy and the light response over a wide range of neutron energies, this data, in the form of a response matrix, can be used to unfold neutron spectra from the detector without the need for TOF. An array of deuterated organic scintillators has been acquired at LLNL for a variety of uses, but first it must be characterized for spectrum unfolding. This includes pulse shape discrimination characterization for separation of neutron and gamma events, and the acquisition of response matrices.