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Radiative Beta Decay of the Free Neutron



R L. Cooper, T E. Chupp, Maynard S. Dewey, Thomas R. Gentile, Hans Pieter Mumm, Jeffrey S. Nico, Alan Keith Thompson, B M. Fisher, I Kremsky, F E. Wietfeldt, E J. Beise, H Breuer, K G. Kiriluk, J Bryne, Kevin Coakley, Changbo Fu


The theory of quantum electrodynamics predicts that the beta decay of the neutron into a proton, electron, and antineutrino is accompanied by a continuous spectrum of emitted photons described as inner bremsstrahlung. While this phenomenon has been observed in nuclear beta decay and electron capture decay for many years, it has only been recently observed in free neutron decay. We present a detailed discussion of an experiment in which the radiative decay mode of the free neutron was observed. In this experiment, the branching ratio for this rare decay was determined by recording photons that were correlated with both the electron and proton emitted in neutron decay. We determined the branching ratio for photons with energy between 15 keV and 340 keV to be (3:09+- 0:32) x 10-3 (68% level of con fidence) where the uncertainty is dominated by systematic e ffects. This value for the branching ratio is consistent with the theoretical predictions. The characteristic energy spectrum of the radiated photons, which diff ers from the uncorrelated background spectrum,is also consistent with the theoretical spectrum.
Physical Review C (Nuclear Physics)


bremsstrahlung, neutron decay, photon detection, photon detector calibration


Cooper, R. , Chupp, T. , Dewey, M. , Gentile, T. , Mumm, H. , Nico, J. , Thompson, A. , Fisher, B. , Kremsky, I. , Wietfeldt, F. , Beise, E. , Breuer, H. , Kiriluk, K. , Bryne, J. , Coakley, K. and Fu, C. (2009), Radiative Beta Decay of the Free Neutron, Physical Review C (Nuclear Physics), [online], (Accessed February 24, 2024)
Created February 1, 2009, Updated October 12, 2021