Abstract
The Alpha-Gamma device at the National Institute of Standards and Technology (NIST) utilizes neutron capture on a totally absorbing 10B deposit to measure the absolute neutron flux of a monochromatic cold neutron beam. Gammas produced by the boron capture are counted using high purity germanium detectors, which are calibrated using a well-measured 239Pu alpha source and the alpha-to-gamma ratio from neutron capture on a thin 10B target. This device has been successfully operated and used to calibrate the neutron flux monitor for the BL2 neutron lifetime experiment at NIST. It is also being used for a measurement of the 6Li(n,t)4He cross section. We shall present its principle of operation along with the current and planned projects involving the Alpha-Gamma device, including the recalibration of the U.S. national neutron standard NBS-1 and (n,f) cross section measurements of 235U.
Highlights
Principle of operationPrecision experiments with low energy neutrons have provided extensive insight into the fundamental physics of particles and other basic and applied areas of scientific discovery
The Alpha-Gamma device installed at the monochromatic beam station NG-6M at the NIST Center for Neutron Research (NCNR) is an absolute neutron flux measurement device that is used in precision calibration of neutron flux monitors, including the one used in the BL2 apparatus
The cold neutron beam will interact with the deposit and the resulting fission product rate will provide a measure of cross section
Summary
Precision experiments with low energy neutrons have provided extensive insight into the fundamental physics of particles and other basic and applied areas of scientific discovery. In addition to its primary focus on neutron scattering experiments, the NCNR guide hall houses experiments in imaging, calibration, and fundamental neutron physics; most notably, a second run of the beam lifetime experiment, BL2, is currently underway as discussed by Hoogerheide, et al elsewhere in these proceedings [1]. The Alpha-Gamma device installed at the monochromatic beam station NG-6M at the NCNR is an absolute neutron flux measurement device that is used in precision calibration of neutron flux monitors, including the one used in the BL2 apparatus. 2. Current measurement campaigns as well as projects planned for the immediate future will be discussed in Sect.
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