[en] The role of ultracold neutrons (UCN) as a very useful probe for studying the problems of fundamental physics is considered. The capabilities for UCN production in a spallation source and its realization at the Manuel Lujan Neutron Scattering Center (MLNSC) are discussed. In a spallation source a proton beam strikes a high-Z target in which approximately 1 neutron per 30 MeV of beam power is produced. The spallation source at MLNSC uses the 800 MeV proton beam from the LANSCE linear accelerator to produce neutrons by spallation on a tungsten target. The long (600-800 μsec) pulse from the linac is first compressed in a storage rind to a pulse width of 270 nsec. The beam extracted from the storage ring is incident on split tungsten target surrounded by four moderators in a flux trap geometry. There are three water moderators and a liquid hydrogen moderators. The beam line being used for UCN production views the liquid hydrogen moderator. The leakage from the moderator peaks at a value of 1 neutron/(eV-sr-proton) and an energy of 0.004 eV (800 m/sec). The moderation time for 400-m/sec neutrons is approximately 100 μsec. The preliminary data gained in the course of testing indicate that the density of UCN at the production point is almost 1/cc

[en] A prototype of a solid deuterium (SD₂) source of Ultra-Cold Neutrons (UCN) is currently being tested at LANSCE. The source is contained within an assembly consisting of a 4 K polyethylene moderator surrounded by a 77 K beryllium flux trap in which is embedded a spallation target. Time-of-flight measurements have been made of the cold neutron spectrum emerging directly from the flux trap assembly. A comparison is presented of these measurements with results of Monte Carlo (LAHET/MCNP) calculations of the cold neutron fluxes produced in the prototype assembly by a beam of 800 MeV protons incident on the tungsten target. A UCN detector was coupled to the assembly through a guide system with a critical velocity of 8 m/s (⁵⁸Ni). The rates and time-of-flight data from this detector are compared with calculated values. Measurements of UCN production as a function of SD₂ volume (thickness) are compared with predicted values. The dependence of UCN production on SD₂ temperature and proton beam intensity are also presented

[en] Ultra-cold neutrons (UCN), neutrons with energies low enough to be confined by the Fermi potential in material bottles, are playing an increasing role in measurements of fundamental properties of the neutron. The ability to manipulate UCN with material guides and bottles, magnetic fields, and gravity can lead to experiments with lower systematic errors than have been obtained in experiments with cold neutron beams. The UCN densities provided by existing reactor sources limit these experiments. The promise of much higher densities from solid deuterium sources has led to proposed facilities coupled to both reactor and spallation neutron sources. In this Letter we report on the performance of a prototype spallation neutron-driven solid deuterium source. This source produced bottled UCN densities of 145±7 UCN/cm³, about three times greater than the largest bottled UCN densities previously reported. These results indicate that a production UCN source with substantially higher densities should be possible

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[en] In this paper, we describe the performance of the Los Alamos spallation-driven solid-deuterium ultra-cold neutron (UCN) source. Measurements of the cold neutron flux, the very low energy neutron production rate, and the UCN rates and density at the exit from the biological shield are presented and compared to Monte Carlo predictions. The cold neutron rates compare well with predictions from the Monte Carlo code MCNPX and the UCN rates agree with our custom UCN Monte Carlo code. The source is shown to perform as modeled. The maximum delivered UCN density at the exit from the biological shield is 52(9) UCN/cc with a solid deuterium volume of ∼1500 cm³.

[en] We describe a simple drift tube counter that has been used as a cosmic ray veto for the UCNA experiment, a first-ever measurement of the neutron beta-asymmetry using ultra-cold neutrons. These detectors provide an inexpensive alternative to more conventional scintillation detectors for large area cosmic ray anticoincidence detectors.

[en] We present the first measurements of the survival time of ultracold neutrons (UCNs) in solid deuterium (SD₂). This critical parameter provides a fundamental limitation to the effectiveness of superthermal UCN sources that utilize solid ortho-deuterium as the source material. These measurements are performed utilizing a SD₂ source coupled to a spallation source of neutrons, providing a demonstration of UCN production in this geometry and permitting systematic studies of the influence of thermal up-scatter and contamination with para-deuterium on the UCN survival time

[en] We report the first measurement of an angular correlation parameter in neutron β decay using polarized ultracold neutrons (UCN). We utilize UCN with energies below about 200 neV, which we guide and store for ∼30 s in a Cu decay volume. The interaction of the neutron magnetic dipole moment with a static 7 T field external to the decay volume provides a 420 neV potential energy barrier to the spin state parallel to the field, polarizing the UCN before they pass through an adiabatic fast passage spin flipper and enter a decay volume, situated within a 1 T field in a 2x2π solenoidal spectrometer. We determine a value for the β-asymmetry parameter A₀=-0.1138±0.0046±0.0021

[en] The Russian-American experiment SAGE began to measure the solar neutrino capture rate with a target of gallium metal in December 1989. Measurements have continued with only a few brief interruptions since that time. In this article we present the experimental improvements in SAGE since its last published data summary in December 2001. Assuming the solar neutrino production rate was constant during the period of data collection, combined analysis of 168 extractions through December 2007 gives a capture rate of solar neutrinos with energy more than 233 keV of 65.4_-3.0^+3.1 (stat) _-2.8^+2.6 (syst) SNU. The weighted average of the results of all three Ga solar neutrino experiments, SAGE, Gallex, and GNO, is now 66.1±3.1 SNU, where statistical and systematic uncertainties have been combined in quadrature. During the recent period of data collection a new test of SAGE was made with a reactor-produced ³⁷Ar neutrino source. The ratio of observed to calculated rates in this experiment, combined with the measured rates in the three prior ⁵¹Cr neutrino-source experiments with Ga, is 0.87±0.05. A probable explanation for this low result is that the cross section for neutrino capture by the two lowest-lying excited states in ⁷¹Ge has been overestimated. If we assume these cross sections are zero, then the standard solar model including neutrino oscillations predicts a total capture rate in Ga in the range of 63 SNU to 66 SNU with an uncertainty of about 4%, in good agreement with experiment. We derive the current value of the neutrino flux produced in the Sun by the proton-proton fusion reaction to be φ_pp^·=(6.0±0.8)x10¹⁰/(cm² s), which agrees well with the pp flux predicted by the standard solar model. Finally, we make several tests and show that the data are consistent with the assumption that the solar neutrino production rate is constant in time.