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Harada, Masahide; Teshigawara, Makoto; Oi, Motoki; Klinkby, E.*; Zanini, L.*; Batkov, K.*; Oikawa, Kenichi; Toh, Yosuke; Kimura, Atsushi; Ikeda, Yujiro
Nuclear Instruments and Methods in Physics Research A, 903, p.38 - 45, 2018/09
Times Cited Count：10 Percentile：70.71(Instruments & Instrumentation)Harada, Masahide; Watanabe, Noboru; Teshigawara, Makoto; Kai, Tetsuya; Maekawa, Fujio; Kato, Takashi; Ikeda, Yujiro
LA-UR-06-3904, Vol.2, p.700 - 709, 2006/06
Pulse characteristics data for every neutron beam line are indispensable in designing devices for neutron scattering experiments of JSNS. A detailed model was built and pulse characteristics of each beam line were estimated using the PHITS code and the MCNP-4C code. These results have been disclosed on the J-PARC homepage since September 2004. Due to changes of moderator shapes in a progress of manufacture design, we observed from the calculation that pulse structures of decoupled moderators were deteriorated, especially, those of pulse tail. We found that this deterioration was caused by leakage neutron from gaps between decouplers and absorbing liners of the reflector. For a final stage of the manufacture design, we carefully tried to find other factors which deteriorated the pulse characteristics. Furthermore, pulse structures of poisoned and unpoisoned decoupled moderators were evaluated with the consideration of heterogeneous burn-up and leakage neutron spectra including high-energy region up to GeV were estimated for each neutron beam hole.
Kai, Tetsuya; Harada, Masahide; Teshigawara, Makoto; Watanabe, Noboru; Kiyanagi, Yoshiaki*; Ikeda, Yujiro
Nuclear Instruments and Methods in Physics Research A, 550(1-2), p.329 - 342, 2005/09
Times Cited Count：18 Percentile：74.82(Instruments & Instrumentation)Neutronic study was performed on coupled hydrogen moderators to maximize time-integrated and pulse-peak intensities of slow neutrons when a large number of beams was required. The total increased with the number of beams, although the average decreased due to a reflector-missing by the beam extraction holes in the reflector. At a large beam extraction angle (25 degree), the spatial distribution of the vector-flux of neutrons was undesirable for a rectangular shape moderator. As an alternative we proposed a cylindrical shape one, resulting in a much improved spatial distribution. In addition, neutronic performance was calculated as a function of the diameter, indicating the optimal diameter was about 140 mm. The cylindrical one gave higher pulse-peak intensities with narrower pulse widths without penalty in time-integrated intensities and pulse decay characteristics, providing a more uniform angle-dependence. Some explanations are given for the difference in the pulse characteristics between the two. We decided to adopt the cylindrical one for the Japanese spallation neutron source.
Harada, Masahide; Watanabe, Noboru; Teshigawara, Makoto; Kai, Tetsuya; Ikeda, Yujiro
Nuclear Instruments and Methods in Physics Research A, 539(1-2), p.345 - 362, 2005/02
Times Cited Count：21 Percentile：78.97(Instruments & Instrumentation)Neutronic studies of decoupled hydrogen moderators were performed by calculations taking into account para hydrogen content, decoupling energy, moderator dimensions/shapes and reflector material. Low-energy parts of calculated spectral intensities with different para hydrogen contents were analyzed by a modified Maxwell function to characterize neutron spectra. The result shows that a 100% para hydrogen moderator gives the highest pulse peak intensity together with the narrowest pulse width and the shortest decay times. Pulse broadening with a reflector was explained by time distributions of source neutrons entering into the moderator through a decoupler. Material dependence of time distribution was studied. A decoupling energy higher than 1 eV does not bring about a large improvement in pulse widths and decay times, even at a large penalty in the peak intensity. The optimal moderator thickness was also discussed for a rectangular parallelepiped shape and a canteen shape moderators.
Kai, Tetsuya; Harada, Masahide; Teshigawara, Makoto; Watanabe, Noboru; Ikeda, Yujiro
Nuclear Instruments and Methods in Physics Research A, 523(3), p.398 - 414, 2004/05
Times Cited Count：36 Percentile：89.19(Instruments & Instrumentation)Neutronic performance of a coupled hydrogen moderator was studied as a function of para hydrogen concentration, moderator thickness, height and premoderator thickness. It was found that a thick (120
140mm) moderator with 100% para hydrogen was optimal to provide the highest time- and energy- integrated neutron intensity below 15 meV together with the highetst possible pulse-peak intensity. Low-energy neutron distribution on the moderator viewed surface was found to exhibit an intensity-enhanced region at a picture frame part near premoderator. The rather peculiar distribution suggested that the moderator and the viewed surface must be designed so as to take the brighter region near premoderator in use.
Harada, Masahide; Teshigawara, Makoto; Watanabe, Noboru; Kai, Tetsuya; Ikeda, Yujiro
Proceedings of ICANS-XVI, Volume 2, p.697 - 706, 2003/07
For two decoupled moderators in JSNS, optimization studies were performed by model calculations using NMTC/JAM and MCNP-4C codes. The model was based on a realistic Target-Moderator-Reflector Assembly. We assumed a para-hydrogen ratio of 100%. The shape of poisoned and unpoisoned moderators is a canteen type with dimensions of 13
12
6.2
cm
. A decoupling energy of about 1 eV was adopted to meet the user's requests. As a decoupler material we selected silver-indium-cadmium alloy. It was found that for the decoupled moderators, especially the poisoned moderator, pulse broadening due to a finite beam-extraction angle (
) was very serious. Therefore, for the poisoned and the unpoisoned moderators were limited to be 7.5
and 17.5, respectively. Cadmium (Cd) was selected as a poison material due to higher cut-off energy than gadolinium and higher peak intensity with narrower pulse width. The poison plate will be placed at 25 mm from the viewed surface which meets the user's requirements.
Kai, Tetsuya; Harada, Masahide; Teshigawara, Makoto; Watanabe, Noboru; Ikeda, Yujiro
Proceedings of ICANS-XVI, Volume 3, p.657 - 666, 2003/07
Neutronic design studies were carried out on the J-PARC coupled H
moderator. The highest time- and energy- integrated intensity below 15 meV, pulse peak intensity at 2 meV and 10 meV, were given by 100% para-H moderators, but the optimal moderator thickness was different for each: more than 220 mm, about 120 mm and 80 mm, respectively. Finally, we concluded 140 mm was the optimal thickness for the 100% para-H coupled moderator. Cold neutron distributions on the moderator viewed surface were found to exhibit an intensity-enhanced region at a picture frame part near premoderator. This rather peculiar distribution suggested that the moderator and the viewed surface must be designed so as to take the brighter region near premoderator in use. The intensity decreases along with beam-extraction angle to the normal direction down to about 70% at 25.4
. Then, we propose a cylindrical shape coupled moderator which brings about a slight intensity decrease for 0 but a increase in the averaged intensity over the angles of interest.
Harada, Masahide; Teshigawara, Makoto; Kai, Tetsuya; Sakata, Hideaki*; Watanabe, Noboru; Ikeda, Yujiro
Journal of Nuclear Science and Technology, 39(8), p.827 - 837, 2002/08
Times Cited Count：18 Percentile：73.17(Nuclear Science & Technology)For a decoupled hydrogen (super critical) moderator, optimization studies have been performed on a premoderator and reflector material (Pb, Be, Fe and Hg) together with the decoupling energy to realize a higher neutronic performance. The result indicated that the best neutronic performance could be obtained for a decoupled H
moderator in a Pb reflector by optimizing the premoderator and adopting an appropriate decoupling energy, even compared with optimized one in a Be reflector.
Harada, Masahide; Teshigawara, Makoto; Kai, Tetsuya; Sakata, Hideaki*; Watanabe, Noboru; Ikeda, Yujiro
JAERI-Research 2001-016, 32 Pages, 2001/03
JAERI-Research-2001-016.pdf:1.74MB
An optimization study on the premoderator, the reflector material choice and a length of the liner is carried out for the design of high performance decoupled hydrogen moderator. NMTC/JAM and MCNP-4C are used for the neutronics calculation. The result indicates that, assuming premoderator dimensions and decoupling energy is controlled, the decoupled hydrogen moderator with a premoderator can provide better pulse characteristics than that without the premoderator for a Be reflector. On the selection of the reflector material, it is clearly shown that Pb and Hg reflectors give merits in using the premoderator for higher intensity and reduction of energy deposition in moderator. It is also shown that a H2O premoderator provides a short tail while a D2O premoderator provides the high peak intensity. Minimum liner length is evaluated to be 20 cm from the viewpoint of neutronics.
Harada, Masahide; Teshigawara, Makoto; Kai, Tetsuya; Sakata, Hideaki*; Watanabe, Noboru; Ikeda, Yujiro
JAERI-Research 2000-014, p.40 - 0, 2000/03
JAERI-Research-2000-014.pdf:2.99MB
no abstracts in English
