Ultracold neutron production and up-scattering in superfluid helium between 1.1 K and 2.4 K

Abstract

Ultracold neutrons (UCNs) were produced in a 4 liter volume of superfluid helium using the PF1B cold neutron beam facility at the Institut Laue-Langevin and then extracted to a detector at room temperature. With a converter temperature of 1.08 K the number of accumulated UCNs was counted to be $91,700\pm 300$. From this, we derive a volumetric UCN production rate of $(6.9\pm 1.7)\mathrm{c}{\mathrm{m}}^{-3}{\mathrm{s}}^{-1}$, which includes a correction for losses in the converter during UCN extraction caused by a short storage time, but not accounting for UCN transport and detection efficiencies. The up-scattering rate of UCNs due to excitations in the superfluid was studied by scanning the temperature between 1.2-2.4 K. Using the temperature-dependent UCN production rate calculated from inelastic neutron scattering data in the analysis, the only UCN up-scattering process found to be present was from two-phonon scattering. Our analysis rules out contributions from the other scattering processes to $\lesssim 10\%$ of their predicted levels.

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• Neutron lifetime measurements and effective spectral cleaning with an ultracold neutron trap using a vertical Halbach octupole permanent magnet array
• Optimizing neutron moderators for a spallation-driven ultracold-neutron source at TRIUMF
• Upgrade of the ultracold neutron source at the pulsed reactor TRIGA Mainz
• A next-generation inverse-geometry spallation-driven ultracold neutron source
• Neutrons on a surface of liquid helium
• The neutron electric dipole moment experiment at the Spallation Neutron Source
• High-power closed-cycle ${}^4$He cryostat with top-loading sample exchange
• Estimated performance of the TRIUMF ultracold neutron source and electric dipole moment apparatus