J-PARC Center ■Development of Experimental Techniques / Facilities at JAEA R&D Centers13-5 Scintillation Neutron Detectors with a High Spatial Resolution=Position-Sensitive Detectors for Single-Crystal Diffractometer in J-PARC=(b) Schematic view
To photomultipliers(c) Measured beam profile

Wavelengthshifting fibers

Clear fibers

9913.0Counts(a) picture

WavelengthShifting fiber(WLSF)

0.9 mm(in full widthat half maximum)

0.0

y.0
elspix

Scintillator (top)
Scintillator (back)

B4C Block27

neutron

Scintillator(133×133 mm)

34.0

pixelsxFig.13-11 A high spatial resolution neutron image detector for iBIX
Wavelength shifting fibers that are sandwiched between scintillator screens collect scintillation light efficiently. Bending
the fibers backward with a radius of 3 mm helps decrease the neutron-insensitive area. The detector measured acollimated beam with a width of 0.3 mm as 0.9 mm in FWHM, demonstrating a high spatial resolution.

(d) Detector module(e) Detector efficiency
Detector efficiency (%)

300 mmDetector headm
300 m(f) SENJU

80Signal processing & Dataaquisition systemExperiment
Theory604020Detectors
0Detector inside(WLSFs)

Thermal neutrons(1.8Å)

0123456Neutron wavelength (Å)

Fig.13-12 A large area neutron image detector for SENJU
One detector module has a neutron-sensitive area of 256 × 256 mm2. The SENJU accommodates 31 detectors,
covering a total scattering angle of 30%. The state-of-the-art detectors make the SENJU a unique and highly efficientinstrument.

Neutron diffraction on a single crystal of protein is aunique technique for identifying the hydrated position of thesample. However, acquiring high-quality data from the protein
has inherent difficulties because the diffraction intensity is
weak and scattered Bragg peaks are very close. A twodimensional neutron detector that has a spatial resolution lessthan 1 mm and a detector efficiency higher than 50% with aminimum dead area is required. To fulfill such specifications,
we have developed a detector that consists of scintillator andwavelength shifting fibers (WLSF) (Fig.13-11). With thisdetector, a neutron is detected through scintillation light. A
spatial resolution of 0.9 mm is achieved by confining thescintillation light to a 0.4-mm thick scintillator and by reading
the light using a 0.5-mm diameter fiber.
We also developed a ZnS/10B2O3 ceramic scintillator thathas a four-fold larger neutron absorption cross section than aconventional ZnS/6LiF scintillator. The detector, which
employs two scintillator screens and the dedicated photon
counting electronics, exhibited a detector efficiency of 50%
for thermal neutrons. This is higher than the conventional
detector efficiency of 35%. The IBARAKI Biological Crystal
Diffractometer (iBIX), populated with 30 such detectors, hada significantly reduced measurement time: only three days fora 1-mm3 protein sample. In contrast, more than a month wasrequired with a conventional instrument built in the Japan
Research Reactor-3 (JRR-3).
We have also developed a new image detector for theSingle-crystal Neutron Diffractometer under Extreme Condition(SENJU) project. The aim of SENJU is to study crystal
structures of materials under extreme environmental conditions,such as low temperatures and high magnetic fields. TheSENJU project requires unique and unprecedented detectorsthat have a spatial resolution of 4 mm, high detector
efficiency, and a large detector to scan a momentum space as
efficiently as possible. We designed a dedicated detector headthat incorporates a 1-mm diameter WLSF placed with aregular pitch of 4 mm (Fig.13-12). With this head, thedetector exhibited a detector efficiency of 40% for thermal
neutrons and the neutron-sensitive area was four times that of
the iBIX detector. The SENJU shortened the measurement
time to only a day for a small sample (1 mm3); this compares
to a few days required for the measurement with a similar
instrument in the JRR-3.
These new scintillation detectors significantly add to thehigh-performance neutron scattering instruments in theJ-PARC. These new types of detectors would also be very
useful in any application that requires measurement of theincident positions of neutrons.

Reference
Nakamura, T. et al., A Large-Area Two-Dimensional Scintillator Detector with a Wavelength-Shifting Fibre Readout for a Time-of-Flight Single-Crystal
Neutron Diffractometer, Nuclear Instruments and Methods in Physics Research A, vol.686, issue 1, 2012, p.64-70.

114 JAEA R&D Review 2012