586 research outputs found
Pulsed UCN production using a Doppler shifter at J-PARC
We have constructed a Doppler-shifter-type pulsed ultra-cold neutron (UCN)
source at the Materials and Life Science Experiment Facility (MLF) of the Japan
Proton Accelerator Research Complex (J-PARC). Very-cold neutrons (VCNs) with
136- velocity in a neutron beam supplied by a pulsed neutron
source are decelerated by reflection on a m=10 wide-band multilayer mirror,
yielding pulsed UCN. The mirror is fixed to the tip of a 2,000-rpm rotating arm
moving with 68- velocity in the same direction as the VCN. The
repetition frequency of the pulsed UCN is and the time width
of the pulse at production is . In order to increase the UCN
flux, a supermirror guide, wide-band monochromatic mirrors, focus guides, and a
UCN extraction guide have been newly installed or improved. The
-equivalent count rate of the output neutrons with longitudinal
wavelengths longer than is ,
while that of the true UCNs is . The spatial density at
production is . This new UCN source enables us to
research and develop apparatuses necessary for the investigation of the neutron
electric dipole moment (nEDM).Comment: 32 pages, 15 fugures. A grammatical error was fixe
Experimental Signature of Medium Modifications for rho and omega Mesons in the 12 GeV p + A Reactions
The invariant mass spectra of e+e- pairs produced in 12-GeV proton-induced
nuclear reactions are measured at the KEK Proton-Synchrotron. On the low-mass
side of the omega meson peak, a significant enhancement over the known hadronic
sources has been observed. The mass spectra, including the excess, are well
reproduced by a model that takes into account the density dependence of the
vector meson mass modification, as theoretically predicted.Comment: 4 pages, 3 figures, Version accepted for Physical Review Lette
Relation of n-value to critical current in bent-damaged Bi2223 composite tape
AbstractThe relation of n-value to critical current of bent-damaged (Bi,Pb)2Sr2Ca2Cu3O10+δ (Bi2223) composite tape was studied experimentally and analytically. The experimental results showed that, under bending strain, the n-value decreased rather slightly with decreasing critical current in comparison with the data obtained under applied tensile strain. The experimentally observed slight decrease in n-value with critical current under bending strain, and the measured changes in critical current and n-value with increasing bending strain, were described satisfactorily by the presented damage evolution model that correlates the extent of damage to variation of bending strain-induced tensile strain in the core along the thickness direction
A diffuse scattering model of ultracold neutrons on wavy surfaces
Metal tubes plated with nickel-phosphorus are used in many fundamental
physics experiments using ultracold neutrons (UCN) because of their ease of
fabrication. These tubes are usually polished to a average roughness of 25-150
nm. However, there is no scattering model that accurately describes UCN
scattering on such a rough guide surface with a mean-square roughness larger
than 5 nm. We therefore developed a scattering model for UCN in which
scattering from random surface waviness with a size larger than the UCN
wavelength is described by a microfacet Bidirectional Reflectance Distribution
Function model (mf-BRDF model), and scattering from smaller structures by the
Lambert's cosine law (Lambert model). For the surface waviness, we used the
statistical distribution of surface slope measured by an atomic force
microscope on a sample piece of guide tube as input of the model. This model
was used to describe UCN transmission experiments conducted at the pulsed UCN
source at J-PARC. In these experiments, a UCN beam collimated to a divergence
angle smaller than was directed into a guide tube with a
mean-square roughness of 6.4 nm to 17 nm at an oblique angle, and the UCN
transport performance and its time-of-flight distribution were measured while
changing the angle of incidence. The mf-BRDF model combined with the Lambert
model with scattering probability reproduced the
experimental results well. We have thus established a procedure to evaluate the
characteristics of UCN guide tubes with a surface roughness of approximately 10
nm.Comment: 15 pages, 11 figure
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