Portable Gamma and Thermal Neutron Detector Using LiI(Eu) Crystals
Portable Gamma and Thermal Neutron Detector Using LiI(Eu) Crystals Simultaneous detection of gamma rays and neutrons emanating from an unknown source has been of special significance and importance to consequence management and first responders since the earliest days of the program. Bechtel Nevada scientists have worked with 6LiI(Eu) crystals and 6Li glass to develop field-operable dual sensors that detect gamma rays and neutrons simultaneously. The prototype 6LiI(Eu) counter, which has been built and tested, is designed to collect data for periods of one second to more than eight hours. The collection time is controlled by thumbwheel switches. A fourpole, high pass filter at 90 KHz reduces microphonic noise from shock or vibration. 6LiI(Eu) crystals generate completely separable gamma-ray and thermal neutron responses. The 6LiI(Eu) rate meter consists of a single crystal 3.8 x 3.8 cm (1.5 x 1.5 in) with a 2.54-cm-(1-in-) thick, annular, high-density, polyethylene ring around the cylinder. Special features are (1) thermal and epithermal neutron detection (0.025eV to 250keV) and (2) typical gamma resolution of 8% at 661.6 keV. Monte Carlo N-Particle calculations for characteristics of gamma spectral behavior, neutron attenuation length, relative neutron and gamma detection efficiency are reported.
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