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Title: A Technique for Determining Neutron Beam Fluence to 0.01% Uncertainty

The achievable uncertainty in neutron lifetime measurements using the beam technique has been limited by the uncertainty in the determination of the neutron density in the decay volume. In the Sussex-ILL-NIST series of beam lifetime experiments, the density was determined with a neutron fluence mon itor that detected the charged particle products from neutron absorption in a thin layer of 6Li or lOB. In each of the experiments, the absolute detection efficiency of the neutron monitor was determined from the measured density of the neutron absorber, the thermal neutron cross section for the absorbing ma terial, and the solid angle of the charged particle detectors. The efficiency of the neutron monitor used in the most recent beam lifetime experiment has since been measured directly by operating it on a monochromatic neutron beam in which the total neutron rate is determined with a totally absorbing neutron detector. The absolute nature of this technique does not rely on any knowl edge of neutron absorption cross sections or a measurement of the density of the neutron absorbing deposit. This technique has been used to measure the neutron monitor efficiency to 0.06% uncertainty. VVe show that a new monitor and absolute neutron detector employingmore » the same technique would be capable of achieving determining neutron fluence to an uncertainty of 0.01%.« less
 [1] ;  [2] ;  [2] ;  [3] ;  [4] ;  [5] ;  [6] ;  [7]
  1. University of Maryland and NIST
  2. National Institute of Standards and Technology (NIST), Gaithersburg, MD
  3. National Institute of Standards and Technology (NIST)
  4. Los Alamos National Laboratory (LANL)
  5. University of Tennessee (UTK) and Oak Ridge National Laboratory (ORNL)
  6. Indiana University, Center for the Exploration of Energy and Matter (CEEM)
  7. Tulane University
Publication Date:
OSTI Identifier:
DOE Contract Number:
Resource Type:
World Scientific Publishing Co. Pte. Ltd., Singapore City, Singapore
Research Org:
Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States). Spallation Neutron Source
Sponsoring Org:
USDOE Office of Science (SC)
Country of Publication:
United States
Neutron lifetime; neutron fluence