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Improved Determination of the Neutron Lifetime

A. T. Yue, M. S. Dewey, D. M. Gilliam, G. L. Greene, A. B. Laptev, J. S. Nico, W. M. Snow, and F. E. Wietfeldt
Phys. Rev. Lett. 111, 222501 – Published 27 November 2013
Physics logo See Synopsis: Discrepancy in Neutron Lifetime Still Unresolved

Abstract

The most precise determination of the neutron lifetime using the beam method was completed in 2005 and reported a result of τn=(886.3±1.2[stat]±3.2[syst])s. The dominant uncertainties were attributed to the absolute determination of the fluence of the neutron beam (2.7 s). The fluence was measured with a neutron monitor that counted the neutron-induced charged particles from absorption in a thin, well-characterized Li6 deposit. The detection efficiency of the monitor was calculated from the areal density of the deposit, the detector solid angle, and the evaluated nuclear data file, ENDF/B-VI Li6(n,t)He4 thermal neutron cross section. In the current work, we measure the detection efficiency of the same monitor used in the neutron lifetime measurement with a second, totally absorbing neutron detector. This direct approach does not rely on the Li6(n,t)He4 cross section or any other nuclear data. The detection efficiency is consistent with the value used in 2005 but is measured with a precision of 0.057%, which represents a fivefold improvement in the uncertainty. We verify the temporal stability of the neutron monitor through ancillary measurements, allowing us to apply the measured neutron monitor efficiency to the lifetime result from the 2005 experiment. The updated lifetime is τn=(887.7±1.2[stat]±1.9[syst])s.

  • Figure
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  • Received 6 September 2013

DOI:https://doi.org/10.1103/PhysRevLett.111.222501

© 2013 American Physical Society

Synopsis

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Discrepancy in Neutron Lifetime Still Unresolved

Published 27 November 2013

Precision measurements of the neutron lifetime differ by about 8 seconds.

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Authors & Affiliations

A. T. Yue1,2,3,*, M. S. Dewey2, D. M. Gilliam2, G. L. Greene3,4, A. B. Laptev5,6, J. S. Nico2, W. M. Snow7, and F. E. Wietfeldt5

  • 1Institute for Research in Electronics and Applied Physics, University of Maryland, College Park, Maryland 20742, USA
  • 2National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA
  • 3University of Tennessee, Knoxville, Tennessee 37996, USA
  • 4Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
  • 5Tulane University, New Orleans, Louisiana 70118, USA
  • 6Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
  • 7Indiana University, Bloomington, Indiana 47408, USA

  • *andrew.yue@nist.gov

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Issue

Vol. 111, Iss. 22 — 27 November 2013

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