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Science Forum Index » Physics Forum » Observation of the radiative decay mode of the free neutron
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 Posted: Thu May 01, 2008 9:05 am |
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Nature 444, 1059-1062 (21 December 2006) | doi:10.1038/nature05390;
Received 31 August 2006; Accepted 25 October 2006
Observation of the radiative decay mode of the free neutron
Jeffrey S. Nico1, Maynard S. Dewey1, Thomas R. Gentile1, H. Pieter
Mumm1, Alan K. Thompson1, Brian M. Fisher2, Isaac Kremsky2, Fred E.
Wietfeldt2, Timothy E. Chupp3, Robert L. Cooper3, Elizabeth J. Beise4,
Kristin G. Kiriluk4, James Byrne5 & Kevin J. Coakley6
Physics Laboratory, National Institute of Standards and Technology,
Gaithersburg, Maryland 20899, USA
Department of Physics, Tulane University, New Orleans, Louisiana
70118, USA
FOCUS and Physics Department, University of Michigan, Ann Arbor,
Michigan 48109, USA
Department of Physics, University of Maryland, College Park, Maryland
20742, USA
Department of Physics and Astronomy, University of Sussex, Brighton
BN1 9QH, UK
Information Technology Laboratory, National Institute of Standards and
Technology, Boulder, Colorado 80305, USA
Correspondence to: Jeffrey S. Nico1 Correspondence and requests for
materials should be addressed to J.S.N. (Email: jnico@nist.gov).
Abstract
The theory of quantum electrodynamics (QED) predicts that beta decay
of the neutron into a proton, electron and antineutrino should be
accompanied by a continuous spectrum of soft photons. While this inner
bremsstrahlung branch has been previously measured in nuclear beta and
electron capture decay, it has never been observed in free neutron
decay. Recently, the photon energy spectrum and branching ratio for
neutron radiative decay have been calculated using two approaches: a
standard QED framework1, 2, 3 and heavy baryon chiral perturbation
theory4 (an effective theory of hadrons based on the symmetries of
quantum chromodynamics). The QED calculation treats the nucleons as
point-like, whereas the latter approach includes the effect of nucleon
structure in a systematic way. Here we observe the radiative decay
mode of free neutrons, measuring photons in coincidence with both the
emitted electron and proton. We determined a branching ratio of (3.13
0.34) 10-3 (68 per cent level of confidence) in the energy region
between 15 and 340 keV, where the uncertainty is dominated by
systematic effects. The value is consistent with the predictions of
both theoretical approaches; the characteristic energy spectrum of the
radiated photons, which differs from the uncorrelated background
spectrum, is also consistent with the calculated spectrum. This result
may provide opportunities for more detailed investigations of the weak
interaction processes involved in neutron beta decay. |
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