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Plastic scintillators are in wide use in radiation portal monitors because of their low cost and availability in large sizes. However, due to their low density and atomic number (Z), they offer low intrinsic efficiency and little to no spectroscopic information. The addition of high-Z constituents to these plastics can greatly increase both their total stopping power and the amount of photo-electric absorption, leading to full-energy deposition and thus spectroscopic information in plastics. In this work, we present the performance of the largest bismuth-loaded plastics to date, showing useful spectroscopic information up to relatively high energy (~1 MeV) and their high stopping power compared the current commercially available plastics. These Bi-loaded plastics are based on 20 wt% Bi-pivalate (8 wt% elemental Bi) dissolved in a polyvinytoluene (PVT) matrix and conventional fast fluors (<10 ns decay time). A comparison of performance between slab and cylindrical plastics of similar volumes is presented and large performance improvements (greater than 9 times the sensitivity to 241Am) are shown when used as a drop-in replacement to conventional PVT based portal monitors.
This work was performed under the auspices of the U.S. DOE by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344, and has been supported by the US DOE, Office of NNSA, NA-22.LLNL-ABS-767130.
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