Magnetic trapping of ultracold neutrons

Abstract

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 4 He. 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 500 ± 155 neutrons are magnetically trapped in each loading cycle, consistent with theoretical predictions. The lifetime of the observed signal, 660 s +290 −170 s, is consistent with the neutron beta-decay lifetime.

Framework for maximum likelihood analysis of neutronβdecay observables to resolve the limits of theV−Alaw

“…Indeed, in such experiments, there are no threshold effects, and the entire proton recoil spectrum is empirically accessible [61,62]. On the other hand, experimental concepts which detect the decay electrons have been under development [63,64].…”

Spin flip loss in magnetic confinement of ultracold neutrons for neutron lifetime experiments

“…In the latter work we used a 1D model for the trapping field. In the present article we have extended this analysis to arbitrary orbits in arbitrary fields in 3D space and report calculations of mean spin-flip rates for the UCNτ system and for multipole fields such as the cylindrical octupole of the HOPE project [25,26] and the Ioffe-type quadrupole trapping fields of [23,34,35]. In all cases relevant to magnetic UCN storage we have established agreement between the semi-classical approach, solving the spin-dependent SE for the time-dependent field seen by the particle in a classical orbit, and a fully quantum mechanical analysis based on the space and spin dependent SE solved in WKB approximation.…”

“…2 if we use values of holding field close to their minima: 0.08 T/0.1 T for HOPE (vertical configuration with B min = 0.013 T/horizontal with B min = 0.09 T) [26] and 0.1 T (0.6 T) for NIST mark 2 (mark 3) with B min ≈ 0.1 T (0.6 T) [34,35].…”

“…(b) Two horizontal Ioffe type quadrupole magnets have been used at NIST [34,35] (versions mark 2 and mark 3). For mark 2 (mark 3) we use maximal fields of, axially: 1.4 T (4.0 T), and radially: 1.3 T (3.9 T), a trap radius of 5 cm (5 cm) and a separation of 0.4 m (0.76 m) between the centers of the end field solenoids; for mark 2, the latter include "bucking" coils [34,35] causing the axial field to drop off more quickly to a minimum of 0.1 T at the trap center.…”

Facile Synthesis of Highly Crystalline and Large Areal Hexagonal Boron Nitride from Borazine Oligomers

“…Difference in electronegativity between boron and nitrogen give rise to permanent dipole such that the h-BN is electrically insulating while graphite is conducting5. The h-BN also has a variety of useful properties such as low dielectric constant6, high thermal conductivity7, thermal and chemical stability8, superior lubrication9, neutron shielding10 and piezoelectricity11. Recently, h-BN films, often dubbed as “white graphene” have been given a considerable attention since graphene was discovered in 200412.…”