Jason Newby

New Organic Crystals for Pulse Shape Discrimination

Efficient, readily-available, low-cost, high-energy neutron detectors can play a central role in detecting illicit nuclear weapons since neutrons are a strong indication for the presence of fissile material such as Plutonium and Highly-Enriched Uranium. The main challenge in detecting fast neutrons consists in the discrimination of the signal from the gamma radiation background. At present, the only well-investigated organic crystal scintillator for fast neutron detection, in a n/gamma mixed field, is stilbene, which while offering good pulse shape discrimination, is not widely used because of its limited availability and high cost.

Neutron detection with single crystal organic scintillators

Detection of high-energy neutrons in the presence of gamma radiation background utilizes pulse-shape discrimination (PSD) phenomena in organics studied previously only with limited number of materials, mostly liquid scintillators and single crystal stilbene. The current paper presents the results obtained with broader varieties of luminescent organic single crystals. The studies involve experimental tools of crystal growth and material characterization in combination with the advanced computer modeling, with the final goal of better understanding the relevance between the nature of the organic materials and their PSD properties. Special consideration is given to the factors that may diminish or even completely obscure the PSD properties in scintillating crystals. Among such factors are molecular and crystallographic structures that determine exchange coupling and exciton mobility in organic materials and the impurity effect discussed on the examples of trans-stilbene, bibenzyl, 9,10- diphenylanthracene and diphenylacetylene.

Demonstration of Emitted-Neutron Computed Tomography to Quantify Nuclear Materials

In this document, we report demonstration of emitted-neutron computed tomography using fast fission neutrons to infer the geometry of sources of special nuclear material (SNM). The imaging system employed in the demonstration is based on a newly constructed array of pixelated neutron detectors that are suitable for arrangement in a close-packed imaging array and whose active volume consists of liquid scintillator EJ-309 which allows neutron-gamma discrimination via pulse shape to enable essentially pure fast-neutron imaging. The system is capable of high quality fast-neutron imaging where tomographic reconstruction of slices through an object resolves neutron sources similar in dimension to a fuel pellet, or about 1 cm. During measurements of Pu MOX fuel rodlet arrays in soup cans at the INL ZPPR facility, the position of a partial defect of a single rodlet containing Pu replaced by one containing depleted uranium (DU) was detected.

Position-Sensitive Fast-Neutron Detector Development in Support of Fuel-Cycle R&D MPACT Campaign

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A PHENIX perspective on soft observables in Heavy Ion Collisions

We present an overview of measurements from the PHENIX experiment focusing on soft observables in nucleus-nucleus collisions. The excellent particle identification of the PHENIX detector at low and intermediate transverse momentum provide an extensive set of measurements in nucleus-nucleus collisions and baseline measurements in p+p and d+Au collisions. Thermalized particle spectra, strong elliptic and radial flow, and HBT measurements reveal the global features of the hot QCD medium produced at RHIC energies while fluctuation measurements probe critical behavior near a phase transition. Collectively these measurements reveal a hot, dense medium with partonic degrees of freedom undergoing a locally-thermalized hydrodynamic expansion.