Plastic scintillators utilizing iridium complex fluorophores offer substantial improvements in light yield, and their light yield is not significantly quenched in compositions with bismuth metalorganic loading, at a loading level of 21 wt% bismuth metal. This new bismuth plastic (Ir-Bi-Plastic) offers improved detection efficiency over commercial plastic scintillators. One application for Ir-Bi-Plastic is in low-cost, portable, and durable dual-particle imaging (DPI) systems supporting nuclear safety, security, and safeguards. However, new materials must undergo investigation using industry standards to quantify their capabilities. In this work, an Ir-Bi-Plastic was experimentally evaluated as a small, pixelated radiographic array in a fast neutron environment, with individual pixel dimensions of 2×2×19 mm. For comparison, identical evaluations were conducted for two similarly sized arrays made from EJ-200 and EJ-256. A separate Ir-Bi-Plastic array with 5×5×20 mm pixels was also evaluated. ASTM methods were leveraged to determine the modulation transfer function and spatial resolution for each array. Edge response measurements of a 2-in thick tungsten block were recorded by pressure coupling all four arrays to a commercial a-Si digital radiographic panel. Experimental results were then compared for all four arrays, and the results demonstrated that the Ir-Bi-Plastic outperforms similar arrays made from EJ-200 and EJ-256 (5 wt% Pb). These findings suggest that DPI systems utilizing Ir-Bi-Plastic hold promise for continued development over older, more traditional, alternatives.
Scintillators are important materials for radiation detection applications such as homeland security, geological exploration, and medical imaging. Scintillators for nuclear nonproliferation applications in particular must have excellent energy resolution in order to distinguish the gamma-ray signatures of potentially dangerous radioactive sources, such as highly enriched uranium or plutonium, from non-threat radioactive sources such as radioactive tracers used in medical imaging. There is an established need for scintillators with energy resolution in the 1-2% range at 662 keV. However, there are challenges surrounding the development of this new generation of high light yield/high resolution scintillators; for example, the high cost of production due to low crystal yield and slow growth process, and crystal inhomogeneity. We will discuss efforts focused on developing recently discovered high performance scintillators K(Sr,Ba)2I5:Eu, Cs4(Ca,Sr)I6:Eu and Cs2Hf(Cl,Br)6 that have potential for meeting nuclear security needs. Growth parameters for these materials have been optimized, allowing the growth of excellent quality single crystals measuring up to one-inch in diameter via the vertical Bridgman technique at translation rates between 1 and 5 mm/h. These scintillators materials have excellent properties with light yields between 30,000 and 120,000 ph/MeV, and energy resolutions between 2.3 and 4.6% at 662 keV.
Eu-doped strontium iodide single crystal growth has reached maturity and prototype SrI2(Eu)-based gamma ray
spectrometers provide detection performance advantages over standard detectors. SrI2(Eu) offers a high, proportional light
yield of >80,000 photons/MeV. Energy resolution of <3% at 662 keV with 1.5” x 1.5” SrI2(Eu) crystals is routinely
achieved, by employing either a small taper at the top of the crystal or a digital readout technique. These methods overcome
light-trapping, in which scintillation light is re-absorbed and re-emitted in Eu2+-doped crystals. Its excellent energy
resolution, lack of intrinsic radioactivity or toxicity, and commercial availability make SrI2(Eu) the ideal scintillator for
use in handheld radioisotope identification devices. A 6-lb SrI2(Eu) radioisotope identifier is described.
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