M. Katagiri

Evaluation of performance for IBARAKI biological crystal diffractometer iBIX with new detectors.

The time-of-flight neutron single-crystal diffractometer iBIX at the next-generation neutron source J-PARC has been upgraded and is available for user experiments on protein samples in particular. Neutron structure analysis of a standard protein sample was carried out in order to evaluate the performance of iBIX.

Readout characteristics of an imaging plate by fast laser pulses

The readout characteristics of an imaging plate (IP) by fast laser pulses have been studied using an alpha-ray source. The total photostimulated luminescence (PSL) detected with the system was proportional to the alpha-ray irradiation time. It can be used for radiation dose measurement. The accumulated radiation information in the IP is decreased by reading PSL signal with the laser pulses. The PSL decay curve in each frequency is well fitted by a single exponential function. Linear dependency of the decay constant on the repeated frequency of the pulse was observed in a frequency range from 60 kHz to 200 kHz. The readout method with fast laser pulses will be useful for development of novel radiation detection system and investigation of successive repeated readout characteristics and fading effects of the IP.

Development of wavelength-shifting-fiber neutron image detector with a fiber-optic taper with a high spatial resolution

The neutron image detector that was based on wavelength-shifting-fibers (WLS fibers) equipped with the fiber-optic taper was developed. By inserting the FOT in between the scintillator and WLS fibers the measured neutron image was magnified on the WLS fibers. We have tested two FOTs; a square-shaped one with a size of 2.6 × 2.6 mm and a round shaped with a diameter of 20 mm. Both FOTs have identical magnification ratios of 3.1. By implementing the larger FOT the detector has the neutron-sensitive area of 314 mm2 with the effective pixel size of 0.17 × 0.17 mm2 while the light transmission rate decreased 20% less compared to that with the small FOT. The detector equipped with the larger FOT exhibited a spatial resolution of 0.26 ±0.07 mm, which was similar to that of the one with the small FOT.

A time-of-flight neutron imaging detector using ZnS/6LiF scintillator and wavelength shifting fibers with high spatial resolution and with low gamma-ray sensitivity

The ZnS scintillator-based two-dimensional detector was developed for time-of-flight neutron imaging with a high spatial resolution and with a low gamma-ray sensitivity. The developed detector based on neutron counting method exhibited a high spatial resolution of less than 100 μm in full width at half maximum with a moderate count rate capability of several tens kcps. Its low gamma-ray sensitivity of less than 10-7 is also of particular interest. The detector is comprised of a thin ZnS/6LiF scintillator screen with crossed wavelength-shifting fiber (WLS fiber) arrays equipped with the fiber optic taper (FOT). Neutron imaging capabilities of the detector have been demonstrated by using a high-intensity pulsed neutron beam at the Materials and Life Science Experimental Facility in the Japan Proton Accelerator Complex (J-PARC).

Development of a wavelength-shifting-fibre-based scintillator neutron detector as an alternative to 3He at J-PARC/MLF

A wavelength-shifting-fibre-based scintillator detector has been developed as an alternative detector to 3He gas. The detector is intended for use in an inelastic neutronscattering instrument at J-PARC. The detector being developed, which is based on the one made for a SENJU diffractometer, is designed to cover a large scattering angle with a moderate pixel size as well as exhibiting a high detection efficiency, low gamma-ray sensitivity and low background count rate. A prototype detector with a pixel size of 20 x 20 mm and a neutron- sensitive area of 320 x 320 mm2 has been constructed. This paper describes the design of the detector and its performance relative to the original SENJU detector.

An empirical formula for calculating the spatial resolution of a wavelength-shifting fibre detector coupled with a ZnS/6LiF scintillator for detecting thermal neutrons

An empirical formula that predicts the spatial resolution of a thermal neutron detector comprising of wavelength-shifting (WLS) fibre arrays coupled with a ZnS/6LiF scintillator screen was derived based on experimental results. The spatial resolutions of the test detectors were measured separately in order to evaluate the contributions due to light spreading within the scintillator and the WLS fibres layers. The empirical formula involved the scintillator thickness and the diameter of the WLS fibres. The results calculated using the derived formula faithfully reproduced the results obtained experimentally with the test detectors, demonstrating the feasibility of using the formula when designing the neutron detecting head for this type of detector.

Evaluation of angular dependence of neutron detection efficiencies of ZnS scintillator detectors

The detection efficiencies of ZnS neutron-sensitive scintillator detector were evaluated as functions of the neutron incidence angle on the scintillator and neutron wavelength using a pulsed neutron beam that generates neutron with wavelengths from 0.5 to 8 Å. ZnS/6LiF and ZnS/10B2O3 scintillator screens with thicknesses of 0.45 and 0.22 mm, respectively, were used for the evaluation. The detection efficiency of each scintillator was strongly influenced by the incidence angle and the neutron wavelength. A fitting model that incorporates both the neutron-absorption and light-escape probabilities reproduced the measured detection efficiencies very well.

Development of two-dimensional scintillation detectors for neutron spin echo spectrometers in J-PARC/MLF

A two-dimensional scintillation detector comprising of a single screen of flat neutron-sensitive scintillator with wavelength shifting fibers read out was developed. The detector was designed to meet the requirements for the modulated intensity by zero effort spectrometer (MIEZE) to be installed in the J-PARC/MLF. The ZnS/10B2O3 scintillator screen that had 0.2±0.05 mm in thickness was implemented to the detector to minimize the time parallax within the scintillator. The detector design and the detector performances are presented.

Novel remote sensor using an imaging plate and wavelength-shifting fibers for dosimetry of gamma rays and neutrons

A novel remote sensing method utilizing an imaging plate was developed for dosimetry of gamma rays and neutrons in reactor or accelerator facilities. One of important research theme for this method is to develop remote sensors because these dosimetries require the multi-point measurements. Therefore, we developed a remote sensor which consists of an imaging plate, band pass light filter, wavelength shifting fibers and side-emission-type light fibers for exciting an imaging plate. The remote sensor was optimized by selecting the bandpass filters. After the optimization, it is confirmed by the basic experiments that the PSL counts can be measured with good S/N ratio and are proportional to gamma-ray doses.

A fast readout method for an imaging plate using wavelength shifting fibers and line-shaped laser

A fast readout method for an imaging plate is proposed using wavelength shifting fibers and line-shaped laser. This method adopts wavelength shifting fiber for signal transmission and line-shaped laser for reading out all pixels of the imaging plate in one axis at the same time, which results in reduction of readout time. To validate the method, the authors have fabricated an experimental system with a rotating mirror and earned out demonstration experiments using CAMAC readout system. In the experiments, two measuring methods such as a photon counting method and a charge integral method were used. The experimental results show that an alpha particle image of 5/spl times/5 mm can be taken within 10 milliseconds in both methods. The spatial resolution of 0.5 mm in the photon counting method was obtained in scanning direction, although the resolution perpendicular to scanning direction was more than 1 mm, which greatly depends on the diameter of the wavelength shifting fibers.