J. S. Butterworth

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-particle and charged-particle traps are widely used for studying both composite and elementary particles, because they allow long interaction times and isolation of particles from perturbing environments. Here we report the magnetic trapping of neutrons. The trapping region is filled with superfluid 4He, which is used to load neutrons into the trap and as a scintillator to detect their decay. Neutrons in the trap have a lifetime 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.

Fluorescence efficiencies of thin scintillating films in the extreme ultraviolet spectral region

Abstract Fluorescence efficiencies of the organic scintillators tetraphenyl butadiene (TPB), p-terphenyl (TPH), and diphenyl stilbene (DPS) are measured relative to sodium salicylate at incident wavelengths of 58.4 and 74.0 nm. Optimum thickness and dopant concentration are determined for maximum fluorescence yield in evaporated, sprayed, and doped plastic films. Measurements made with alpha (α) particle induced scintillations in gaseous argon (a broad band vacuum ultraviolet light source) were in good agreement with those made using the line source. Transparent scintillator doped plastic films have been developed which yield fluorescence efficiencies comparable to that of sodium salicylate. Evaporated films show the highest fluorescent yields, reaching almost four times the efficiency of sprayed sodium salicylate. On the other hand, doped plastic films offer some advantages.

Magnetic trapping of ultracold neutrons

Three-dimensional magnetic confinement of neutrons is reported. Neutrons are loaded into an Ioffe-type superconducting magnetic trap through inelastic scattering of cold neutrons with

A removable cryogenic window for transmission of light and neutrons

{}^{4}\mathrm{He}.

A demountable cryogenic feedthrough for plastic optical fibers

Scattered neutrons with sufficiently low energy and in the appropriate spin state are confined by the magnetic field until they decay. The electron resulting from neutron decay produces scintillations in the liquid helium bath that results in a pulse of extreme ultraviolet light. This light is frequency downconverted to the visible and detected. Results are presented in which

Invited Article: Development of high-field superconducting Ioffe magnetic traps

500\ifmmode\pm\else\textpm\fi{}155

Magnetically stabilized luminescent excitations in hexagonal boron nitride

neutrons are magnetically trapped in each loading cycle, consistent with theoretical predictions. The lifetime of the observed signal,

RADIATIVE DECAY OF THE METASTABLE HE2(A 3SIGMA +U) MOLECULE IN LIQUID HELIUM

{660}_{\ensuremath{-}170}^{+290} \mathrm{s},

Detecting ionizing radiation in liquid helium using wavelength shifting light collection

is consistent with the neutron beta-decay lifetime.

Progress towards magnetic trapping of ultra-cold neutrons

A demountable, superfluid-tight window for the transmission of neutrons and light has been developed. A fluorocarbon polymer (Teflon) film is both the window and sealing gasket. Transmission of blue light and bursting pressure are measured for films of varying thicknesses.