An organic glass scintillator developed by Sandia National Laboratories was characterized in terms of its light output and pulse shape discrimination (PSD) properties and compared to commercial liquid (EJ-309) and plastic (EJ-276) organic scintillators. The electron light output was determined through relative comparison of the 137Cs Compton edge location. The proton light yield was measured using a double time-of-flight technique at the 88-Inch Cyclotron at Lawrence Berkeley National Laboratory. Using a tunable broad-spectrum neutron source and an array of pulse-shape-discriminating observation scintillators, a continuous measurement of the proton light yield was performed for EJ-309 (200 keV–3.2 MeV), EJ-276 (170 keV–4.9 MeV), and the organic glass (50 keV–20 MeV). Finally, the PSD properties of the organic glass, EJ-309, and EJ-276 were evaluated using an AmBe source and compared via a figure-of-merit metric. The organic glass exhibited a higher electron light output than both EJ-309 and EJ-276. Its proton light yield and PSD performance were comparable to EJ-309 and superior to that of EJ-276. With these performance characteristics, the organic glass scintillator is well poised to replace current state-of-the-art PSD-capable scintillators in a range of fast neutron detection applications.
The light output, time resolution, pulse shape discrimination (PSD), neutron light output, and interaction position reconstruction of melt-cast small-molecule organic glass bar scintillators were measured. The trans-stilbene organic scintillator detects fast neutrons and gamma rays with high efficiency and exhibits excellent PSD, but the manufacturing process is slow and expensive and its light output in response to neutrons is anisotropic. Small-molecule organic glass bars offer an easy-to-implement and cost-effective solution to these problems. These properties were characterized to evaluate the efficacy of constructing a compact, low-voltage neutron and gamma-ray imaging system using organic glass bars coupled to silicon photomultiplier arrays. A complete facility for melt-casting organic glass scintillators was setup at the University of Michigan. 6×6×50 mm3 glass bars were produced and the properties listed above were characterized. The first neutron image using organic glass was produced in simple backprojection.
The light output, time resolution, pulse shape discrimination (PSD), neutron light output, and interaction position reconstruction of melt-cast small-molecule organic glass bar scintillators were measured. The trans-stilbene organic scintillator detects fast neutrons and gamma rays with high efficiency and exhibits excellent PSD, but the manufacturing process is slow and expensive and its light output in response to neutrons is anisotropic. Small-molecule organic glass bars offer an easy-to-implement and cost-effective solution to these problems. These properties were characterized to evaluate the efficacy of constructing a compact, low-voltage neutron and gamma-ray imaging system using organic glass bars coupled to silicon photomultiplier arrays. A complete facility for melt-casting organic glass scintillators was setup at the University of Michigan. 6×6×50 mm3 glass bars were produced and the properties listed above were characterized. The first neutron image using organic glass was produced in simple backprojection.
The multi-institution Single-Volume Scatter Camera (SVSC) collaboration led by Sandia National Laboratories (SNL) is developing a compact, high-efficiency double-scatter neutron imaging system. Kinematic emission imaging of fission-energy neutrons can be used to detect, locate, and spatially characterize special nuclear material. Neutron-scatter cameras, analogous to Compton imagers for gamma ray detection, have a wide field of view, good event-by-event angular resolution, and spectral sensitivity. Existing systems, however, suffer from large size and/or poor efficiency. We are developing high-efficiency scatter cameras with small form factors by detecting both neutron scatters in a compact active volume. This effort requires development and characterization of individual system components, namely fast organic scintillators, photodetectors, electronics, and reconstruction algorithms. In this presentation, we will focus on characterization measurements of several SVSC candidate scintillators. The SVSC collaboration is investigating two system concepts: the monolithic design in which isotropically emitted photons are detected on the sides of the volume, and the optically segmented design in which scintillation light is channeled along scintillator bars to segmented photodetector readout. For each of these approaches, we will describe the construction and performance of prototype systems. We will conclude by summarizing lessons learned, comparing and contrasting the two system designs, and outlining plans for the next iteration of prototype design and construction.
The scintillation anisotropy effect for proton recoil events has been investigated in five pure organic crystalline materials: Anthracene, trans-stilbene, p-terphenyl, bibenzyl, and diphenylacetylene (DPAC). These measurements include the characterization of the scintillation response for one hemisphere of proton recoil directions in each crystal. In addition to standard measurements of the total light output and pulse shape at each angle, the prompt and delayed light anisotropies are analyzed, allowing for the investigation of the singlet and triplet molecular excitation behaviors independently. This paper provides new quantitative and qualitative observations that make progress toward understanding the physical mechanisms behind the scintillation anisotropy. These measurements show that the relationship between the prompt and delayed light anisotropies is correlated with a crystal structure, as it changes between the pi-stacked crystal structure materials (anthracene and p-terphenyl) and the herringbone crystal structure materials (stilbene, bibenzyl, and DPAC). The observations are consistent with a model in which there are preferred directions of kinetic processes for the molecular excitations. These processes and the impact of their directional dependences on the scintillation anisotropy are discussed.
