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12 September 2016 Improving the time response of a gamma/neutron liquid detector
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A pulsed neutron source is used to interrogate a target, producing secondary gammas and neutrons. In order to make good use of the relatively small number of gamma rays that emerge from the system after the neutron flash, our detector system must be both efficient in converting gamma rays to a detectable electronic signal and reasonably large in volume. Isotropic gamma rays are emitted from the target. These signals are converted to light within a large chamber of a liquid scintillator. To provide adequate time-of-flight separation between the gamma and neutron signals, the liquid scintillator is placed meters away from the target under interrogation. An acrylic PMMA (polymethyl methacrylate) light guide directs the emission light from the chamber into a 5-inch-diameter photomultiplier tube. However, this PMMA light guide produces a time delay for much of the light. Illumination design programs count rays traced from the source to a receiver. By including the index of refraction of the different materials that the rays pass through, the optical power at the receiver is calculated. An illumination design program can be used to optimize the optical material geometries to maximize the ray count and/or the receiver power. A macro was written to collect the optical path lengths of the rays and import them into a spreadsheet, where histograms of the time histories of the rays are plotted. This method allows optimization on the time response of different optical detector systems. One liquid scintillator chamber has been filled with a grid of reflective plates to improve its time response. Cylindrical detector geometries are more efficient.
Conference Presentation
© (2016) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Robert M. Malone, Robert A. Buckles, Anemarie DeYoung, Irene Garza, Daniel K. Frayer, Morris I. Kaufman, George L. Morgan, Andrew W. Obst, Robert S. Rundberg, Jim Tinsley, Tom B. Waltman, and Vincent W. Yuan "Improving the time response of a gamma/neutron liquid detector", Proc. SPIE 9969, Radiation Detectors: Systems and Applications XVII, 99690D (12 September 2016);

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