Performance of Large Neutron Detectors Containing Lithium-Gadolinium-Borate Scintillator

Abstract

This paper describes the development and testing of a neutron counter, spectrometer, and dosimeter that is compact, efficient, and accurate. The 1.3 liter detector head for this instrument is a composite detector with an organic scintillator containing uniformly distributed 6 Li6 nat Gd 10 B3O9:Ce (LGB:Ce) microcrystals. Moderating neutrons that have slowed sufficiently in the plastic, capture in one of the Lithium-6, Boron-10, or Gadolinium-157/155 atoms in the LGB:Ce scintillator, which then releases the capture energy in a characteristic cerium emission pulse. The measured captured pulses indicate the presence of neutrons. When a scintillating fluor is present in the plastic, the light pulse resulting from the neutron moderating in the plastic is paired with the LGB:Ce capture pulse to identify the energy of the neutron. This data was used to assist in the unfolding of the neutron spectra. The unfolded spectra were then validated with known spectra, at both neutron emitting isotopes and fission/accelerator facilities, Los Alamos Neutron Science Center (LANSCE), Edwards Accelerator Laboratory (EAL) at Ohio University. The instrument can measure neutrons and their spectra over the range between 0.8 MeV and 150 MeV with an average uncertainty in neutron rate of only +/-8%.

Tuning the index of refraction of a polyvinyl toluene and polystyrene copolymer toward a heterogenous, index‐matched neutron detector

“…The most common practice is to buy partially polymerized monomer formulations (called resins in the neutron detection industry) from Eljen Technologies from which plastic scintillators are bulk‐polymerized into the desired shape; but this results in translucent (not transparent) plastic when combining different resins (such as PS and PVT). Some studies propose the use of glass/polymer composite designs, but due to a focus on neutronics, they have not discussed the effect or importance of refractive index to these designs 11,14,34 . Yet, these studies still acknowledge that benefits exist to a composite detector design.…”

“…Some studies propose the use of glass/polymer composite designs, but due to a focus on neutronics, they have not discussed the effect or importance of refractive index to these designs. 11,14,34 Yet, these studies still acknowledge that benefits exist to a composite detector design. One of the most similar studies to our work is the dissertation of Foster 23 in which a 6 Li bearing glass scintillator that was doped with cerium (GS-20, Scintacor) was cast within a PVT matrix to form a composite detector.…”

“…The photons from these two pulses need to be accurately and sensitivity detected, often by a photomultiplier tube at one end of the detector. The key shortcoming of current heterogeneous capture‐gated neutron detectors is inefficiency of light transmission due to the cloudiness of the material, as seen in previous work with lithium gadolinium borate (LGB) crystals suspended in a composite matrix 11–14 . The mismatch in the index of refraction severely limits the ability of pulses of light to reach the photodetector, limiting the sensitivity of the detector.…”

OPTICAL PROPERTIES AND RADIATION RESPONSE OF Li ION-DOPED CsI SCINTILLATOR CRYSTAL

“…For neutron detection, a constituent ion with a high neutron absorption section such as 6 Li is necessary. Another attractive feature of Li is its very low cross section for gamma interactions [7]. The neutron active material initiates the light production by releasing energy charged particles or gamma rays when the neutron is captured.…”