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

Magnetic trapping of neutrons

Accurate measurement of the lifetime of the neutron (which is unstable to beta decay) is important for understanding the weak nuclear force and the creation of matter during the Big Bang. Previous measurements of the neutron lifetime have mainly been limited by certain systematic errors; however, these could in principle be avoided by performing measurements on neutrons stored in a magnetic trap. Neutral and charged particle traps are widely used tool for studying both composite and elementary particles, because they allow long interaction times and isolation from perturbing environments. Here we report the magnetic trapping of neutrons. The trapping region is filled with superfluid 4-He, which is used to load neutrons into the trap and as a scintillator to detect their decay. Neutrons have a lifetime in the trap of 750 +330/-200 seconds, mainly limited by their beta decay rather than trap losses. Our experiment verifies theoretical predictions regarding the loading process and magnetic trapping of neutrons. Further refinement of this method should lead to improved precision in the neutron lifetime measurement