Kazuhiko Soyama

The neutron reflectometer (C3-1-2) at the JRR-3M reactor at JAERI

Abstract A neutron reflectometer has been installed at the cold neutron guide tube (C3-1-2) of the JRR-3M reactor at JAERI. Incident neutrons for the reflectometer have a long wavelength of 12.6 A, with a wavelength resolution of 3.2%. The reflectometer has the advantage of a large reflection angle which is appropriate for studies of low- q and off-specular phenomena. The neutron intensity reduction due to the long wavelength is substantially compensated by the relatively coarse beam divergence and wavelength resolution. The reflectometer is mounted in vertical geometry to yield a beam of 3 × 40 mm 2 and is applicable to measurements of mirror systems formed on flat substrates. Applications of the reflectometer to neutron optics and polymer studies are demonstrated and discussed.

Enhancement of reflectivity of multilayer neutron mirrors by ion polishing: optimization of the ion beam parameters

Abstract The reflectivity of multilayer mirrors depend on the interface roughness created during deposition of the layers. In order to smoothen the interfaces, we have investigated the influence of argon ion bombardment on the interface roughness of a Ni/Ti multilayer deposited by ion beam sputtering. The dependencies of ion polishing time, ion acceleration energy and incident angle on the interface roughness were studied to optimize the conditions of Ar + ion polishing. It was observed that the reflectivities and the evaluated interface roughness of multilayers are obviously improved by using ion polishing.

Optimization of a micro-strip gas chamber as a two-dimensional neutron detector using gadolinium converter

Abstract A micro-strip gas chamber (MSGC) has been under development as a two-dimensional position sensitive detector for neutron scattering experiments at the high-intensity proton accelerator facilities. The MSGC requirements as a neutron detector are high counting rate, high detection efficiency, high positional resolution, stability and large area coverage. The purpose of this paper is to verify the properties of Gadolinium as a MSGC converter. The arrangements of a capillary plate and MSGC gas pressure have been optimized by simulation of a Gadolinium converter. As a result of that, a position resolution of 160xa0μm and n/γ ratio of 200 were obtained at the gas pressure of 0.02xa0atm. In view of γ-ray sensitivity, the further improvement is required for practical applications.

A two-dimensional gas detector with individual readouts for neutron detection with a high spatial resolution and fast temporal response

A gaseous neutron-imaging detector with individual signal readouts was developed for a high spatial resolution and a fast temporal response. The system comprises a multiwire head, a gas chamber with 541 channels, fast amplifier-shaper-discriminator boards, a logic circuit for position calculation and encoding, and a fast data-acquisition system. The developed prototype detector incorporating 40×40 channels exhibited a temporal response of ∼100ns (pulse width of the amplified signal) and a spatial resolution of 0.9 and 1.4mm (full width at half maximum) in the x- and y-directions, respectively, with a gas pressure of 4.2-atm helium with 1.8-atm CF4.

Novel instrument system for discriminating secondary particles in high-spatial-resolution neutron detection

A new instrument system with the capability of secondary-particle discrimination (InSPaD) was studied for the development of two-dimensional (2D) neutron detectors (NDs) filled with helium-3 gas and with high spatial resolution. The InSPaD can discriminate between tracks of a proton and a triton created in the nuclear reaction 3He(n,p)T by simply setting the level of the discriminator appropriately in each signal channel, and the system exhibits a high spatial resolution, high counting rate, low background, and stability. The InSPaD identifies the tracks of a proton and a triton on the basis of the length of the tracks, identifies the secondary particles, and calculates the incident positions of neutrons accurately in real time. Simulations of the 2D ND equipped with InSPaD revealed spatial resolutions of 0.46 mm in full width at half maximum for a 10% mixture of C2H6 with helium-3 at 0.3 MPa, and of 0.52 mm for a 20% mixture of argon with helium-3 at 0.5 MPa. The simulated results of the ranges of second...

Developments of a small d-spacing multilayer neutron mirror and the supermirror neutron guide tube at the JRR-3M in JAERI

Abstract The ion-polishing method is applied to the fabrication of Ni/Ti and Ni/Mn multilayers in combination with an Ar+ ion-beam sputtering deposition. The influences of the ion-polishing time, the ion-acceleration energy and the incident angle of ions on the interface roughness between layers were investigated using a high-resolution transmission electron microscopy (TEM). The TEM result showed the remarkable decrease of the interface roughness of Ni/Ti and Ni/Mn multilayers by ion polishing. Ion-polished multilayer mirrors have shown high reflectivities in X-ray and neutron reflectometries. The half-length in the upstream side of the nickel guide tube, which was installed at the thermal beam hole of the JRR-3M at JAERI has been replaced by a supermirror guide tube with a critical angle of 2θcNi. The result showed a remarkable increase in the neutron intensity at the exit of the neutron guide tube.

Modified spin-echo method using cold neutron spin interferometry with RF flippers

Abstract We have been developing a modified spin-echo method using a cold neutron spin interferometry with radio frequency flippers, which is similar to “Mieze spectrometer”. The performances of the method are discussed.

Dimensional Stability of Uranium Silicide Plate-Type Reactors at Transient Condition

This paper describes the result of transient experiments using low enriched uranium silicide plate-type fuel for research reactors. The pulse irradiation was carried out at Nuclear Safety Research Reactor (NSRR) in Japan Atomic Energy Research Institute. The results obtained were: 1. At fuel plate temperature of below 400°C, a good dimensional stability of the tested fuel was kept. No fuel failure occurred. 2. At a plate temperature of about 540°C, a local crack was initiated on the AI-3%Mg alloy cladding. Once the cladding temperature exceeded the melting point of 640°C, the fuel plate was degraded much by increased bowing and cracking of the denuded fuel meat occurred after relocation of molten Al cladding. Despite of these degradation, neither fragmentation of the fuel plate nor mechanical energy generation occurred up to the cladding temperature of 971 °C. 3. At the temperatures of around 925°C, the reaction of silicide particles with molten Al in the matrix and that of cladding occurred, forming Al r...

Cold neutron spin interferometry and its application to modified spin echo methods

Abstract We propose three kinds of modified neutron spin echo methods using cold neutron spin interferometry, which is based on the coherent superposition principle of the neutron spin. Two kinds of the modified methods are based on a novel quantum precession of neutron spin by multilayer spin splitters and another method on time dependent spin interferometry using RF flippers. The performances of the last type are discussed and the firmer two methods are described in other proceedings.

Development of Drabkin energy filters for JSNS project

Abstract We have a plan to install Drabkin energy filters for neutron spectrometers at the Japanese Spallation Neutron Source (JSNS) project. Combined with a high-intensity coupled moderator, a Drabkin energy filter could be very useful to obtain a high-resolution polarized beam with higher intensity than a beam from a decoupled moderator. Hence, it could bring about a breakthrough for more efficient use of neutrons at neutron spectrometers. We have developed a Drabkin energy filter which has 10 periods of spatially oscillating magnetic field and measured spin–flip probabilities as functions of field strength and of neutron wavelength. In this paper, results of the performance tests of Drabkin energy filters are presented and discussed.