M. Ebine

A wavelength-shifting-fibre-based scintillator neutron detector implemented with the median point calculation method

Median point calculation (MPC) method for scintillator neutron detectors operating in photon-counting mode has been developed. The method was applied to a wavelength-shifting (WLS)-fibre-based neutron detector in order to improve its pixel size and spatial resolution. The original detector was modified for a demonstration experiment performed using the SENJU neutron diffraction instrument at J-PARC (Japan Proton Accelerator Research Complex). The detector head comprised 64 × 2 WLS fibres arranged in the x and y directions at a pitch of 4 mm. The WLS fibres were sandwiched between two ZnS/10B2O3 scintillator screens. The developed MPC method used the number of photons detected by each WLS fibre as a weight when calculating the positions of neutrons. The test detector implemented with the MPC method demonstrated that the effective pixel size and the spatial resolution were improved to 2 mm, corresponding to half the pitch of the WLS fibres.

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.

High-spatial-resolution neutron image detector based on wavelength-shifting fiber read out for time-of-flight measurements

A wavelength-shifting-fiber based neutron image detector with a spatial resolution of less 200 μm was developed. The detector had a capability of neutron imaging with a temporal resolution of several μs. The detector equipped with a ZnS/6LiF scintillator where the scintillation light was read out with individual fibers based on a photon counting method. The fiber-optic tapers (FOTs) were implemented in between the scintillator and the fibers to magnify a neutron image. The prototype detector that equipped with the FOTs exhibited the spatial resolution that was improved by an order better compared that with the original detector. This kind of detector would be a unique and powerful tool for the energy-selective neutron radiography at a pulsed neutron source.

Development of a position-sensitive scintillation neutron detector for a new protein single-crystal diffractometer at J-PARC MLF

A high-spatial-resolution, large-area position-sensitive scintillation-based neutron detector module has been developed for a new time-of-flight Laue single-crystal diffractometer to be constructed at J-PARC MLF. A first prototype detector implementing commercial 6Li:ZnS screens was produced based on a scintillator/wavelength-shifting fibre technology. The detector exhibited a spatial resolution of 2.5 mm with a neutron-sensitive area of 320 × 320 mm2. We report on an initial evaluation of the detector performance, including its spatial resolution, detection efficiency and long-term background measurement, and also provide a brief description of a new neutron instrument.

Diagnosis of neutron sensitivity within a scintillator/wavelength-shifting fiber coil element by using a collimated pulsed neutron beam

We have developed a position-sensitive tubular scintillation neutron detector as an alternative to a 3He gas based detector. The detector comprises a number of individual neutron-sensitive elements, where a pair of wound wavelength-shifting fiber coils is sandwiched with two rolled ZnS/6LiF scintillator screens in each element. Position-dependent neutron sensitivity within the scintillator / wavelength-shifting fiber coil (SFC) element was evaluated by using a collimated pulsed neutron beam at the J-PARC MLF. The collimated beam that has a size of 1 × 1 mm2 scanned over the SFC element. Neutron counts were recorded and plotted as a function of incident beam position. The scanning results showed less neutron sensitivity at the juncture of the rolled scintillator screens, which indicated a lack of scintillator materials due to imperfect manufacturing process.

A 64 × 64 cm area position-sensitive scintillation neutron detector as an alternative to helium-3 gas based detector

A two-dimensional scintillation neutron detector that has neutron-sensitive area of 64 × 64 cm² was developed for thermal neutron scattering instruments. The detector extensively used ZnS scintillation screens doped with ¹⁰B or ⁶Li and wavelength shifting fibers technology. The detector is designed to have a pixel size of 20 × 20 mm² to cover a large area with a small number of electronics channel for demonstration. The scintillation light was read out from both sides of each WLS fiber in order to increase a collected light. The prototype detector exhibited a detection efficiency of 50% for 1.9-Å neutrons, which was similar to the detector developed in the past that has a neutron-sensitive size of 26 × 26 cm².

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.

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.