71 research outputs found
Investigating solid N as a new source of ultra-cold neutrons
The dynamical structure factor of solid N in the phase
(K) is measured at the IN4 time-of-flight spectrometer at the Institut
Laue Langevin, and the potential performance of this substance as a UCN
converter is assessed. The cross-section to down-scatter neutrons to ultra-cold
neutron energies is determined as a function of incident energy, as well as the
up-scattering mean free path. The UCN production cross-section is found to be
approximately 20% of that of deuterium. However, UCN with energy 181 neV have
an up-scattering mean free path of 46 cm at K, which is times
larger than deuterium. Therefore, a large volume N source
may produce an improved UCN density if sufficient isotopic purity can be
achieved.Comment: 7 pages, 6 figure
New Understanding of Ultra-Cold Neutron Production in Solid Deuterium
Our recent neutron scattering measurements of phonons and other
quasi-particle excitations in solid deuterium (sD) and the extraction of
the density of states for phonons and rotational transitions in sD2 have led us
to a new understanding of the production of ultra-cold neutrons (UCN) in sD2.
This new picture is somehow different to earlier published results for sD2. The
cross section for UCN production in sD2 has been determined by using the
density of states G1(E) in combination with the incoherent approximation and by
a direct calibration of our measured neutron cross sections with the known
cross section of the J=1 -> 0 rotational transition in deuterium. Both methods
deliver new data on this cross section and agree quite well with direct
measurements of this energy averaged UCN production cross section.Comment: 4 pages, 6 figure
Neutron velocity distribution from a superthermal solid 2H2 ultracold neutron source
We have determined for the first time the velocity distribution of neutrons from a solid 2H2 ultracold neutron (UCN) source. The spectrum rises sharply above 4.5m/s and has a maximum around 7m/s after transport in an 8m long guide. The number of neutrons in the UCN velocity range (< 7m/s) may be increased by a factor of two by placing the experiment 1m above the UCN source leve
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
Testing isotropy of the universe using the Ramsey resonance technique on ultracold neutron spins
Physics at the Planck scale could be revealed by looking for tiny violations
of fundamental symmetries in low energy experiments. In 2008, a sensitive test
of the isotropy of the Universe using has been performed with stored ultracold
neutrons (UCN), this is the first clock-comparison experiment performed with
free neutrons. During several days we monitored the Larmor frequency of neutron
spins in a weak magnetic field using the Ramsey resonance technique. An
non-zero cosmic axial field, violating rotational symmetry, would induce a
daily variation of the precession frequency. Our null result constitutes one of
the most stringent tests of Lorentz invariance to date.Comment: proceedings of the PNCMI2010 conferenc
An Improved Neutron Electric Dipole Moment Experiment
A new measurement of the neutron EDM, using Ramsey's method of separated
oscillatory fields, is in preparation at the new high intensity source of
ultra-cold neutrons (UCN) at the Paul Scherrer Institute, Villigen, Switzerland
(PSI). The existence of a non-zero nEDM would violate both parity and time
reversal symmetry and, given the CPT theorem, might lead to a discovery of new
CP violating mechanisms. Already the current upper limit for the nEDM
(|d_n|<2.9E-26 e.cm) constrains some extensions of the Standard Model.
The new experiment aims at a two orders of magnitude reduction of the
experimental uncertainty, to be achieved mainly by (1) the higher UCN flux
provided by the new PSI source, (2) better magnetic field control with improved
magnetometry and (3) a double chamber configuration with opposite electric
field directions.
The first stage of the experiment will use an upgrade of the RAL/Sussex/ILL
group's apparatus (which has produced the current best result) moved from
Institut Laue-Langevin to PSI. The final accuracy will be achieved in a further
step with a new spectrometer, presently in the design phase.Comment: Flavor Physics & CP Violation Conference, Taipei, 200
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
- …