Efficiency Calibration for Measuring the 12C(n, 2n)11C Cross Section
One possible inertial confinement fusion diagnostic involves tertiary neutron activation via the 12C(n, 2n)11C reaction. A recent experiment to measure this cross section involved coincidence counting annihilation gamma rays produced by the positron decay of 11C. This requires an accurate value for the full-peak coincidence efficiency of the NaI detector system. The GEANT 4 toolkit was used to develop a Monte-Carlo simulation of the detector system which can be used to calculate the required efficiencies. For validation, simulation predictions have been compared with the results of three experiments. In the first, full-peak coincidence positron annihilation efficiencies were measured for 22Na positrons that annihilate in a small plastic scintillator. In the second and third, NIST-calibrated 22Na and 68Ge sources were placed between copper and graphite disks. A comparison of calculated with measured efficiencies, as well as 12C(n, 2n)11C cross sections, are presented.
57th Annual Meeting of the APS Division of Plasma Physics, Savannah, GA, Nov. 16-20, 2015; XXXV Annual Rochester Symposium for Physics Students, University of Rochester, Rochester, NY., April 2, 2016; Omega Laser User’s Group Meeting, Laboratory for Laser Energetics, Rochester, NY, April 27-29, 2016; 2015 APS Division of Plasma Physics Outstanding Undergraduate Poster Award.
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