Motoki Ooi

Performance of Optical Devices for Energy-Selective Neutron Imaging in NOBORU at J-PARC

The NeutrOn Beam-line for Observation and Research Use (NOBORU) is a day-1 neutron instrument serving as a test beam port at the Materials and Life Science Experimental Facility of the Japan Proton Accelerator Research Complex. Energy-selective neutron imaging is one of the more important research activities performed with NOBORU. To obtain a high spatial resolution with low background environment in the imaging experiment, improved neutron optics is necessary. Therefore, a rotary collimator to control the spatial resolution with high neutron intensity and a neutron filter device to control the neutron spectral intensity and gamma ray intensity are designed and installed on the middle of the beam-line. It is found from the results of a neutron radiography test that neutron transmission images with high spatial resolution (~50 m) can be obtained using the smallest hole in the rotary collimator. It is also confirmed that the remote-controlled filter device introduced in front of the rotary collimator can control the intensity of neutrons and gamma rays with only a small increase of the background. In particular, as bulk lead plates and bismuth single crystal plates attenuate the prompt gamma rays while only slightly sacrificing neutron intensity, neutrons in the epithermal neutron region can be easily measured.

Off-gas processing system operations for mercury target vessel replacement at J-PARC

An off-gas processing system was installed in the J-PARC spallation neutron source to reduce radioactivity of xenon-127 and tritium contained in a helium cover gas in a surge tank of a mercury circulation system to obey the regulation by law. In addition to this role it has been utilized to a purging process before the target vessel replacement and an air-flow control procedure to minimize uncontrollable radioactivity release during the replacement. An standard and urgent model plans of the off-gas processing system operation were established indicating that 31 days were required at least to replace the target vessel.

Measurements of neutronic characteristics of rectangular and cylindrical coupled hydrogen moderators

ABSTRACT Extensive simulation calculations were performed in the design studies of the coupled hydrogen moderator for the pulsed spallation neutron source of the Japan Proton Accelerator Research Facility (J-PARC). It was indicated that a para-hydrogen moderator had an intensity-enhanced region at the fringe part, and that pulse shapes emitted from a cylindrical para-hydrogen moderator gave higher pulse-peak intensities with narrower pulse widths than those from a rectangular one without penalizing the time-integrated intensities. To validate the peculiar distribution and advantages in pulse shapes experimentally, some measurements were performed at the neutron source of the Hokkaido University electron linear accelerator facility. It was observed that the neutron intensity was enhanced at edges of the para-hydrogen moderators, whereas it decreased at the same part of the ortho-rich-hydrogen moderator, where the dimension of those moderators was 50 mm in thickness and 120 mm in width and height. The spatial distribution and pulse shapes were also measured for a cylindrical coupled para-hydrogen moderator that has the same dimensions as for the coupled moderator employed for J-PARC. The measured results from the cylindrical moderator were consistent with the results obtained in the design studies for the moderator for J-PARC.

Development of a Three-dimensional Computed Tomography System using High-speed Camera at a Pulsed Neutron Source

The neutron energy resolved three-dimensional imaging system using a high-speed video camera has been newly developed at Japan Proton Accelerator Research Complex (J-PARC). The aim for this research is to investigate more rapidly a spatial distribution of several elements and crystals in various kinds of materials or substances. A high-speed video camera (CMOS, 1300 k frame/sec) of the present system allows us to obtain TOF images consecutively resolved into narrow energy ranges in the pulsed neutron energy region from 0.01 eV to a few keV. We confirmed that the neutron transmission ratio obtained by the present system was consistent with that of theoretical expectation when a step-wedge sample made of Fe, from 5 mm to 10 mm in thickness, was used as a sample. And three-dimensional images reconstructed by the Filtered Back Projection method could be successfully enhanced the image contrast of specific materials by selecting neutron energy. The results show that there is the possibility to apply the present system for practical use in near future.

Upgrade of Monitoring and Operation Systems for the MLF-GCS Base on EPICS and CSS

The monitoring and operation (MO) system for the general control system (GCS) of the Materials and Life Science Experimental Facility (MLF) was upgraded. The MLF-GCS comprises programmable logic controllers (PLCs), operator interfaces (OPIs) for integral control and interlock systems, and shared servers. The system controls various components of the pulsed spallation neutron source such as a mercury target and hydrogen moderators. The MO system is used for monitoring, alarm notification and remote control from the MLF control room. The upgraded MO system operates with the EPICS framework, the OPI of Control System Studio (CSS), and the server software of PostgreSQL. The upgraded system has been operating since January 2014 without serious trouble. This paper describes an overview of the work experience upgraded MO system.

Custom-made Shutter Block for Imaging Instrument "RADEN" at J-PARC

A novel energy-resolved neutron imaging system “RADEN” has been constructed at BL22 at the Materials and Life Science Experimental Facility (MLF) at J-PARC. RADEN was designed for conventional radiography and tomography as well as for Bragg-edge transmission, resonance absorption analysis, and visualization of the magnetic field. Good energy and wavelength resolution of pulsed neutron source at the MLF is fully utilized in this instrument. To maximize flexibility of neutron brightness, beam divergence, and field of view at the sample position, a custom-made shutter block with triple inserts was designed and replaced with the original block, which had a single insert.