The neutron typically beta decays into a proton, electron, and antineutrino. In some decays, it can be accompanied by a high energy photon. We recently performed the rst observation of the radiative beta decay branch for the free neutron with photons of energy 15 keV to 340 keV. We performed the experiment in the bore of a superconducting magnet where electron, proton, and photon signals were measured. A bar of bismuth germanate scintillating crystal coupled to an avalanche photodiode served as the photon detector that operated in the cryogenic, high magnetic eld environment. The branching ratio for this energy region was measured to be (3:130:34)103 and is consistent with theoretical calculations. An experiment is underway to measure the branching ratio with an improved precision of 1 % relative standard uncertainty and to measure the photon energy spectrum. In this paper, the apparatus modi cations to reduce the systematic uncertainties will be described. Central to these improvements is the development of a 12-element detector based on the original photon detector design that will improve the statistical sensitivity. During data acquisition, a detailed calibration program will be performed to improve the systematic uncertainties. The development of these modi cations are currently underway, and the second run of the experiment will commence in July 2008.
Citation: Nuclear Instruments & Methods
Pub Type: Journals
beta decay, neutron, photodiode, radiative