Setsuo Satoh

Development of a neutron detector based on a position-sensitive photomultiplier

A neutron scintillation detector based on a position-sensitive photomultiplier has been developed for neutron spin echo and small angle neutron scattering measurements. This photomultiplier has good spatial resolution, less than 1 mm2. The detection efficiency of gamma ray background is very low for using a thin ZnS/6LiF scintillator. The effective area of this detector is around 60 cm2.

Counting-type neutron imaging detectors of the energy-resolved neutron imaging system RADEN at the J-PARC/MLF

The recently commissioned Energy-Resolved Neutron Imaging System, RADEN, located at the J-PARC Materials and Life Science Experimental Facility (MLF), is the worlds first dedicated high-intensity, pulsed neutron imaging instrument. In addition to conventional radiography and tomography, the wide bandwidth and accurate measurement of neutron energy by time-of-flight is utilized to perform energy-resolved neutron imaging. Such techniques allow direct imaging of the macroscopic distribution of microscopic properties of materials in situ, including crystallographic structure and internal strain, nuclide-specific density and temperature distributions, and internal/external magnetic fields. To carry out such measurements in the high-rate, high-background environment at RADEN, we use cutting-edge detector systems, recently developed in Japan, employing micro-pattern detectors or fast Li-glass scintillators with high-speed, Field Programmable Gate Array-based data acquisition. These counting-type detectors offer sub-μs time resolution, high neutron count rates, and event-by-event gamma rejection. The available detectors offer a range of spatial resolutions from 0.3 to 3 mm and counting rates from 0.6 to 8 Mcps. In the present paper, we show the performance of these detectors as measured at RADEN. We also consider planned improvements to the detector systems that will allow us to achieve finer spatial resolutions by several factors and order-of-magnitude higher count rates.

Magnetic excitations in MnP

We performed inelastic neutron scattering experiments on a three-dimensional magnetic system MnP, which is a ferromagnetic inter-metallic compound below TC = 291 K and transitions into a screw state at T* = 47 K. Using newly developed high resolution chopper spectrometer (HRC) and triple axis spectrometer LTAS (for E = 0?2 meV), 6G (for E = 2?8 meV) TAS1 (for E = 10-35 meV), we succeeded in observing the excitations from low energy to Brillouin zone center. We assumed isotropic 6 exchange parameters, and calculated dispersion relation using Heisenberg model for 2-sub lattices. We confirm that nearest neighbor (n.n) exchange parameters Jm are J > 0 (ferromagnetic interaction), the next nearest neighbor (n.n.n) exchange parameters are J < 0 (anti-ferromagnetic interaction), We conclude that the competition between n.n and n.n.n would be the cause of helimagnetic structure in MnP.

Neutron counting type imaging detector with super-resolution technique

A combination of a neutron image intensifier and a photomultiplier tube array was developed as a neutron imaging device for time-of-flight measurement. The device had an advantage in the neutron counting measurement because of the proportionality to the neutron intensity. A problem was in poor spatial resolution by the photomultiplier tube array, so the super-resolution ability based on the center-of-mass calculation was attached to the newly developed data taking system. We confirmed its ability of time-of-flight measurement through the trial experiment. The super-resolution system also operated without failure.

New Neutron Beam Monitor Based on GEM

The high-intensity neutron total diffractometer (NOVA) constructed in BL21 of MLF [1] in J-PARC is one of the world’s most intense diffractometers. Since NOVA can observe structural changes in a very short time, it is a very powerful system for in-situ measurements. Because a time-slice measurement is usually performed in in-situ measurements, NOVA has to monitor the amount of incident neutrons with high accuracy. Therefore, an incident neutron beam monitor with the ability to monitor high counts is one of the key components of NOVA. We had already developed a two-dimensional neutron detector with a Gas Electron Multiplier (GEM) [2] as the incident neutron beam monitor of NOVA [3]. The GEM-based detector is a good neutron detector, but its electronics is obsolete and it is becoming more difficult to offer it as a new purchase. To overcome this problem, we developed a new neutron beam monitor (nGEM), which is an upgraded system that follows the basic design concept of the GEM-based detector. The nGEM is a gas-flow radiation detector that can measure charged particles from a n( 10 B, ) 7 Li nuclear reaction. The nGEM has a compact body of dimensions 524 mm × 254 mm × 50 mm. An Application Specific Integrated Circuit (ASIC) for pulse shaping and a Field Programmable Gate Array (FPGA) for online processing are also installed in the onboard electronics of the nGEM, which is able to transfer data directly to a PC via a network. The thermal neutron efficiency of the nGEM depends on the thickness of an ■■■ JPS Conf. Proc. , 036019 (2015)

Spin Waves in Ferromagnetic Phase of MnP

Inelastic neutron scattering experiments on an intermetallic compound, MnP, were performed by using a chopper spectrometer as well as triple axis spectrometers. Spin waves were observed in the ferromagnetic phase in the entire Brillouin zone along the a*- and b*-axes. The observed dispersion relations of spin waves were well described by an isotropic Heisenberg interaction adding a single ion anisotropy with two sub-lattices.