No abstract available

[en] Making use of a back-to-back type double fission chamber and a lead slowing-down spectrometer driven by a 46 MeV electron linear accelerator, the fission cross sections of Am-241, Am-242m and Am-243 have been measured relative to that of U-235 from 0.1 eV to 10 keV with the energy resolution of about 40 % full width at half maximum. Each of the measured result has been compared with (1) the evaluated nuclear data in ENDF/B-VI and JENDL-3.2, and (2) the existing experimental data, whose evaluated and measured data were broadened by the energy resolution function of the spectrometer

No abstract available

[en] Evaluations of radiation dose at the site boundary for the Material and Life Science Experimental Facility (MLF) at J-PARC were carried out supposing that the mercury used as the neutron target happened to leak from the mercury circulation system during 1 MW operation. As a result of the evaluation, the dose of external exposure at the site boundary was estimated to be 30 μSv, which was almost given by the radioactive noble gas produced via spallation reactions. The inner exposure of radioactive mercury and tritium was estimated to be 0.1 μSv in total. Since the estimated dose was enough low in comparison with a personal annual dose from natural radioactivity, even though the event scenario was made conservatively, it was shown that MLF has high safety margin for the leak of radioactivity. (author)

[en] Neutronic performance of a coupled hydrogen moderator was studied as a function of para hydrogen concentration, moderator thickness and height, premoderator thickness, etc. for the J-PARC spallation neutron source. It was found that a thick (140 mm) moderator with 100% para-hydrogen was optimal to provide a high time- and energy-integrated neutron intensity below 15 meV and high pulse-peak intensities at lower energies. Distribution of the cold neutrons on a moderator viewed surface was studied and found to exhibit an intensity-enhanced region at the fringe part near the premoderator. This rather peculiar distribution suggested that the moderator and the viewed surface must be designed so as to take the full advantage of the brighter region near the premoderator

[en] Making use of a back-to-back type double fission chamber and a lead slowing-down spectrometer driven by a 46 MeV electron linear accelerator, the fission cross sections of Am-241, Am-242m and Am-243 have been measured relative to that of U-235 from 0.1 eV to 10 keV with the energy resolution of about 40% full width at half maximum. Each of the measured result has been compared with (1) the evaluated nuclear data in ENDF/B-VI and JENDL-3.2, and (2) the existing experimental data, whose evaluated and measured data were broadened by the energy resolution function of the spectrometer. (author)

[en] Making use of a lead slowing-down spectrometer coupled to a 46 MeV electron linear accelerator and a back-to-back type double fission chamber, the fission cross sections of Am-241, Am-242m and Am-243 have been measured relative to that of U-235 from 0.1 eV to 10 keV with the energy resolution of about 40 % full width at half maximum. Each of the measured result has been compared with (1) the evaluated nuclear data in ENDF/B-VI and JENDL-3.2, and (2) the existing experimental data, for which the evaluated and the experimental data were broadened by the energy resolution function of the spectrometer. (author)

[en] Mercury used as a spallation neutron target at JSNS (J-PARC Spallation Neutron Source) is highly activated by proton beam operation. In order to evaluate the feasibility of hands-on maintenance after nominal beam operation with 1 MW in the hot cell where a mercury circulation system was installed, gamma dose measurements and gamma spectroscopy analysis were carried out after low power operation during the commissioning period. By analyzing the data, it was found that radioactive spallation products adhered to the inner surface of piping wall of the circulation system and those significantly raised the dose rates in the hot cell. In order to discuss about measures for future hot-cell entry, the gamma dose rates after the nominal operation were evaluated based on the measured data obtained in this work. (author)

[en] A general control system for the Materials and Life Science Experimental Facility (MLF-GCS) at J-PARC has an advanced and independent system for control of the mercury target, including a circulation system with a large amount of mercury, three moderators with supercritical hydrogen, and cooling systems with radioactive water. Although the MLF-GCS is an independent system, it works closely with the accelerator and other facility control systems within J-PARC. The MLF-GCS consists of several subsystems of integral control and interlock, network, server, timing distribution systems, and personnel protection system (PPS). The design and construction of MLF-GCS has progressed for the first proton beam injection in 2008. After finishing the construction of most of the MLF-GCS subsystems, the commissioning on operation and control of the whole MLF has started step by step in 2007. During short period before the first beam injection, the trial operations, performance tests, and improvements of the MLF-GCS subsystems have been executed under restricted conditions. After the first beam injection in May 2008, the subsystems have been improved according to experience on the beam operations, the administrative structure for the MLF operation shift has been established, and the stable and efficient operations of the MLF-GCS has been realized. This paper reports on the commissioning on the MLF operation and control from April 2007 to March 2009. (author)

[en] The 1-MW spallation neutron source constructed in the Materials and Life Science Experimental Facility under the Japan Proton Accelerator Research Complex (J-PARC) project provides neutrons available for variety of neutron scattering experiments conducted at neutron instruments through neutron beam lines, where neutrons are produced by 3-GeV proton induced spallation reactions in a mercury target followed by moderation through a super-critical hydrogen moderator surrounded by a reflector. Neutron beam shutter systems were installed at the neutron beam line to extract and/or shield neutrons. The shutter control system was designed in order that users were able to open/close shutters at experimental halls during a beam-time and facility's personnel could move shutters for adjustment at vicinity of neutron shutter drive mechanism room in maintenance period. It was also designed to keep the primary condition that personnel was allowed to enter the instrument room when the shutter was closed. This condition was integrated in the Personnel Protection System (PPS) to secure the safety of personnel. Components were designed to enhance reliability of the control system as follows: a shutter close position was detected by two kinds of devices of a mechanical limit switch and a rotary encoder, and the power supply for the shutter system was connected with an uninterruptible power supply (UPS) to prevent loss of signals in case of a power failure. (author)