Magnetically Stabilized Luminescent Excitations in Hexagonal Boron Nitride

Magnetically stabilized luminescence is observed in hexagonal boron nitride. The luminescence is induced by absorption of cold neutrons and is in the visible region. In the absence of a magnetic field, the photon emission level is observed to decay over several hundred seconds. A fraction of this luminescence can be suppressed if the temperature is T <~ 0.6 K and the magnetic field is B >~ 1.0 T. Subsequent to irradiation and suppression, luminescence can be induced by an increase in T or lowering of B. Possible explanations include stabilization of triplet states or the localization and stabilization of excitons.Comment: 11 pages, 7 figures, to appear in the Journal of Luminescenc

Detecting ionizing radiation in liquid helium using wavelength shifting light collection

Detectors for counting low energy less than 1 MeV ionizing events in liquid helium are developed and characterized. These devices employ wavelength shifting fluors to convert extreme ultraviolet EUV helium scintillation light to the visible, allowing transport of signal light to room temperature. Three technological approaches are developed and tested wavelength shifting fiber, composite acrylic tube, and diffuse reflecting tube of expanded teflon. The tube based detectors have been used to detect magnetically trapped neutrons. All of the technological approaches have utility in other experiments, such as a more sensitive measurement of the neutron electric dipole moment and the monitoring of the low energy solar neutrino flu

Time dependence of liquid helium fluorescence

The time dependence of extreme ultraviolet EUV fluorescence following an ionizing radiation event in liquid helium is observed and studied in the temperature range from 250 mK to 1.8 K. The fluorescence exhibits significant structure including a short 10 ns strong initial pulse followed by single photons whose emission rate decays exponentially with a 1.6 mu s time constant. At an even longer time scale, the emission rate varies as 1 time inversely proportional to the time after the initial pulse . The intensity of the 1 time component from beta particles is significantly weaker than those from alpha particles or neutron capture on 3He. It is also found that for alpha particles, the intensity of this component depends on the temperature of the superfluid helium. Proposed models describing the observed fluorescence are discusse