For visualization of flows in superfluid 4He, an excited helium molecule (excimer) 4He2* is an ideally suitable flow tracer, because it has a molecular size with a minimum influence to flow, and follows only normal-component flow around 1K but only vortices below 0.5 K. However, to visualize flow fields in 3D, small clouds (clusters) of 4He2* are required, whose generation method has not been established. To generate such clusters, we proposed the use of neutron-3He absorption reaction. In the proof-of-principle experiments, we have confirmed the 4He2* generation, while the detail of clusters still remains undetermined. The concept, methods, progress, and present status are shown.
A new ultra-cold neutron source has been developed by TUCAN collaboration aiming to measure neutron electric dipole moment at a precision of 10-27 ecm. Ultra-cold neutrons are extremely slow neutrons of which the kinetic energy is below several hundred neV. Therefore, UCNs are totally reflected at the surface of certain materials and can be confined in a material bottle.
Measurements of neutron - noble gas scattering cross sections were obtained at the low divergence branch of BL05 at J-PARC MLF. For this measurement a recently developed simple small angle scattering set up was utilized to measure the neutron momentum transfer spectra for all of the noble gases of natural isotopic abundance. We found a very interesting discrepancy between our measured value for He and existing values in the literature from neutron interferometry. The n-He scattering process is a few body interaction whose theoretical prediction is in progress, therefore our measurement may provide unique insight for few body nuclear physics.
We developed a technique of spin-contrast-variation neutron reflectivity (SCV-NR) for structural analyses of multilayer films. The SCV-NR curves of the polystyrene monolayer film were precisely reproduced using a common set of structural parameters and neutron scattering length density at each proton polarization. This result ensures that SCV-NR curves are not deformed by inhomogeneous PH due to the spin-diffusion mechanism. The number of structural parameters of the lamellar microphase-separated poly(styrene-block-isoprene) thin film is too large to determine with a single unpolarized reflectivity curve only. However, these parameters converged through the global analysis of the SCV-NR curves. In this manner, SCV-NR determines the structure of multilayer films while excluding the incorrect structural model that accidentally accounts for a single unpolarized reflectivity curve only.