First observation of trapped high-field seeking ultracold neutron spin states

Ultracold neutrons were stored in a volume, using a magnetic dipole field shutter. Radial confinement was provided by material walls. Low-field seeking neutrons were axially confined above the magnetic field. High-field seeking neutrons are trapped inside the magnetic field. They can systematically shift the measured neutron lifetime to lower values in experiments with magnetic confinement

Losses and depolarization of ultracold neutrons on neutron guide and storage materials

At Institut Laue-Langevin (ILL) and Paul Scherrer Institute (PSI), we have measured the losses and depolarization probabilities of ultracold neutrons on various materials: (i) nickel-molybdenum alloys with weight percentages of 82/18, 85/15, 88/12, 91/9, and 94/6 and natural nickel Ni100, (ii) nickel-vanadium NiV93/7, (iii) copper, and (iv) deuterated polystyrene (dPS). For the different samples, storage-time constants up to ∼460s were obtained at room temperature. The corresponding loss parameters for ultracold neutrons, η, varied between 1.0×10−4 and 2.2×10−4. All η values are in agreement with theory except for dPS, where anomalous losses at room temperature were established with four standard deviations. The depolarization probabilities per wall collision β measured with unprecedented sensitivity varied between 0.7×10−6 and 9.0×10−6. Our depolarization result for copper differs from other experiments by 4.4 and 15.8 standard deviations. The β values of the paramagnetic NiMo alloys over molybdenum content show an increase of β with increasing Mo content. This is in disagreement with expectations from literature. Finally, ferromagnetic behavior of NiMo alloys at room temperature was found for molybdenum contents of 6.5 at.% or less and paramagnetic behavior for more than 8.7 at.%. This may contribute to solving an ambiguity in literature

Improved measurement of the neutron absorption cross section for very low velocities

The absorption cross section of natural Gd and isotopic enriched 157Gd for ultra-cold neutrons (UCN) as a function of the velocity has been measured within a time-of-flight-experiment. Particular attention is paid to small velocities in the region of a few m/s. This is intended to determine the validity of the 1/v-law governing absorption cross sections in this region and the resulting divergence at v=0. The experiment does not show any significant violation of 1/v for v>3 m/s

A magnetic trap for high-field seeking neutron spin states

A first experimental demonstration of a new type of magnetic trap for ultra-cold neutrons is presented. High-field seeking spin-states are trapped in a potential formed by the magnetic field of a straight wire and a repulsive coating on the wire surface. Life-times of the trapped neutrons of 60 s could be observed. This configuration can in principle be used to form bound states of the wave function on the surface of the wire to probe new forces at short distances. Further applications include the use as a guide and selector for perfectly polarized neutrons

A magnetically shielded room with ultra low residual field and gradient

A versatile and portable magnetically shielded room with a field of (700 ± 200) pT within a central volume of 1 m × 1 m × 1 m and a field gradient less than 300 pT/m, achieved without any external field stabilization or compensation, is described. This performance represents more than a hundredfold improvement of the state of the art for a two-layer magnetic shield and provides an environment suitable for a next generation of precision experiments in fundamental physics at low energies; in particular, searches for electric dipole moments of fundamental systems and tests of Lorentz-invariance based on spin-precession experiments. Studies of the residual fields and their sources enable improved design of future ultra-low gradient environments and experimental apparatus. This has implications for developments of magnetometry beyond the femto-Tesla scale in, for example, biomagnetism, geosciences, and security applications and in general low-field nuclear magnetic resonance (NMR) measurements