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Title: Precision determination of absolute neutron flux

A technique for establishing the total neutron rate of a highly-collimated monochromatic cold neutron beam was demonstrated using an alpha–gamma counter. The method involves only the counting of measured rates and is independent of neutron cross sections, decay chain branching ratios, and neutron beam energy. For the measurement, a target of 10B-enriched boron carbide totally absorbed the neutrons in a monochromatic beam, and the rate of absorbed neutrons was determined by counting 478 keV gamma rays from neutron capture on 10B with calibrated high-purity germanium detectors. A second measurement based on Bragg diffraction from a perfect silicon crystal was performed to determine the mean de Broglie wavelength of the beam to a precision of 0.024%. With these measurements, the detection efficiency of a neutron monitor based on neutron absorption on 6Li was determined to an overall uncertainty of 0.058%. We discuss the principle of the alpha–gamma method and present details of how the measurement was performed including the systematic effects. We further describe how this method may be used for applications in neutron dosimetry and metrology, fundamental neutron physics, and neutron cross section measurements.
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  1. National Inst. of Standards and Technology (NIST), Gaithersburg, MD (United States)
  2. Indiana Univ., Bloomington, IN (United States)
  3. Univ. of Tennessee, Knoxville, TN (United States); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  4. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Publication Date:
Report Number(s):
Journal ID: ISSN 0026-1394
Grant/Contract Number:
AC52-06NA25396; SC0005925; FG02- 03ER41258; PHY-1306942; 70NANB14H299
Accepted Manuscript
Journal Name:
Additional Journal Information:
Journal Volume: 55; Journal Issue: 4; Journal ID: ISSN 0026-1394
Research Org:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org:
USDOE Office of Science (SC). Nuclear Physics (NP) (SC-26); National Inst. of Standards and Technology (NIST), Gaithersburg, MD (United States); National Science Foundation (NSF)
Country of Publication:
United States
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY; alpha counting; absolute neutron counting; cold neutron; neutron beam; neutron wavelength
OSTI Identifier: