Cold neutrons with energy less than several meV are good probes for material research, and they h... more Cold neutrons with energy less than several meV are good probes for material research, and they have been available on large neutron facilities, whereas it is not commonly available on compact accelerator-driven neutron source. RIKEN Accelerator-driven Neutron Source (RANS) is a pulsed neutron facility which provides thermal neutrons and high energy neutrons at several MeV. We started a project to implement a cold neutron moderator for RANS to broaden cold neutrons applications. A cold neutron moderator system with a mesitylene moderator at 20K and a polyethylene pre-moderator at room temperature in the slab geometry was designed for RANS. So far, the thickness of the pre-moderator and mesitylene have been optimized to get the highest cold neutron flux by using a Monte Carlo simulation code, PHITS. Graphite reflector dimensions were also proven to have significant effect to increase the cold neutron intensity.
Physical Review B Condensed Matter and Materials Physics, 2007
We measured an absolute ortho- D2 concentration of gas samples taken from irradiated liquid D2 sa... more We measured an absolute ortho- D2 concentration of gas samples taken from irradiated liquid D2 samples as a function of the integrated radiation dose and the irradiation time by means of a frequency-resolved Raman spectroscopy to study the ortho- D2 conversion mechanism under irradiation. The measurement was carried out by irradiating liquid ortho- D2 at a temperature of 25K with Bremsstrahlung photons, which were produced by bombarding tantalum with 33MeV electrons, and whose absolute fluxes were determined experimentally by employing a foil activation method. The obtained ortho- D2 concentration was found to decrease from 98% to 82% monotonically with increasing the radiation dose, irrespective of the electron-beam power. This fact clearly indicates the important role of a radiation-induced breakup effect of the ortho D2 under the present experimental conditions of radiation dose and irradiation time. The obtained conversion rate is ten times faster than the evaluated value based on an existing model, requiring an alternate mechanism to enhance the conversion.
Applied Physics a Materials Science Processing, Dec 1, 2002
The spallation neutron source of KEK(KENS) was renewed by replacing the whole target-moderator-re... more The spallation neutron source of KEK(KENS) was renewed by replacing the whole target-moderator-reflector assembly (TMRA) with a new tantalum-clad tungsten target. Gadolinium poison, giving a sharper pulse, was installed in the ambient moderator. The new target was developed to increase the source intensity by about 20% compared to the former tantalum target. The neutron performance was measured with several spectrometers. The cold-neutron intensity, which in the former TMRA had decreased to about 30% of its initial state, was recovered. The epithermal-neutron fluxes were increased as the neutronic design calculations indicated. The scattered-neutron profile showed low background and became more symmetrical with the shorter tail. With the total-scattering spectrometer, the radial distribution function shows better resolution in position. As a whole, the new KENS is quite able to investigate the materials of interest.
ABSTRACT Neutron resonance absorption radiography is a technique to enhance neutron transmission ... more ABSTRACT Neutron resonance absorption radiography is a technique to enhance neutron transmission images of specific nucleus at neutron resonance energies. Demonstration measurements by using a lithium-glass pixel type scintillator and a gas electron multiplication (GEM) neutron detector were carried out at NOBORU beam line in MLF/J-PARC for sodium, manganese, cobalt, copper, zinc, molybdenum, cadmium, indium, tantalum and gold. To discuss advantages of the resonance absorption radiography the mass attenuation coefficient at resonance energy of each element was compared to that at 25 meV. In addition a visibility index derived by a resonance peak cross section and a relative width (full width at half maximum divided by its resonance energy) was proposed to summarize visibility of the neutron resonance absorption radiography for natural elements. The values of visibility index and the resonance energy indicated that large advantages of the resonance absorption radiography were obtainable for the following elements: sodium (Na), manganese (Mn), cobalt (Co), rhodium (Rh), silver (Ag), cadmium (Cd), indium (In), xenon (Xe), cesium (Cs), samarium (Sm), europium (Eu), dysprosium (Dy), erbium (Er), thulium (Tm), hafnium (Hf), tantalum (Ta), tungsten (W), rhenium (Re), iridium (Ir) and gold (Au). (C) 2013 The Authors. Published by Elsevier B.V.
Cold neutrons with energy less than several meV are good probes for material research, and they h... more Cold neutrons with energy less than several meV are good probes for material research, and they have been available on large neutron facilities, whereas it is not commonly available on compact accelerator-driven neutron source. RIKEN Accelerator-driven Neutron Source (RANS) is a pulsed neutron facility which provides thermal neutrons and high energy neutrons at several MeV. We started a project to implement a cold neutron moderator for RANS to broaden cold neutrons applications. A cold neutron moderator system with a mesitylene moderator at 20K and a polyethylene pre-moderator at room temperature in the slab geometry was designed for RANS. So far, the thickness of the pre-moderator and mesitylene have been optimized to get the highest cold neutron flux by using a Monte Carlo simulation code, PHITS. Graphite reflector dimensions were also proven to have significant effect to increase the cold neutron intensity.
Physical Review B Condensed Matter and Materials Physics, 2007
We measured an absolute ortho- D2 concentration of gas samples taken from irradiated liquid D2 sa... more We measured an absolute ortho- D2 concentration of gas samples taken from irradiated liquid D2 samples as a function of the integrated radiation dose and the irradiation time by means of a frequency-resolved Raman spectroscopy to study the ortho- D2 conversion mechanism under irradiation. The measurement was carried out by irradiating liquid ortho- D2 at a temperature of 25K with Bremsstrahlung photons, which were produced by bombarding tantalum with 33MeV electrons, and whose absolute fluxes were determined experimentally by employing a foil activation method. The obtained ortho- D2 concentration was found to decrease from 98% to 82% monotonically with increasing the radiation dose, irrespective of the electron-beam power. This fact clearly indicates the important role of a radiation-induced breakup effect of the ortho D2 under the present experimental conditions of radiation dose and irradiation time. The obtained conversion rate is ten times faster than the evaluated value based on an existing model, requiring an alternate mechanism to enhance the conversion.
Applied Physics a Materials Science Processing, Dec 1, 2002
The spallation neutron source of KEK(KENS) was renewed by replacing the whole target-moderator-re... more The spallation neutron source of KEK(KENS) was renewed by replacing the whole target-moderator-reflector assembly (TMRA) with a new tantalum-clad tungsten target. Gadolinium poison, giving a sharper pulse, was installed in the ambient moderator. The new target was developed to increase the source intensity by about 20% compared to the former tantalum target. The neutron performance was measured with several spectrometers. The cold-neutron intensity, which in the former TMRA had decreased to about 30% of its initial state, was recovered. The epithermal-neutron fluxes were increased as the neutronic design calculations indicated. The scattered-neutron profile showed low background and became more symmetrical with the shorter tail. With the total-scattering spectrometer, the radial distribution function shows better resolution in position. As a whole, the new KENS is quite able to investigate the materials of interest.
ABSTRACT Neutron resonance absorption radiography is a technique to enhance neutron transmission ... more ABSTRACT Neutron resonance absorption radiography is a technique to enhance neutron transmission images of specific nucleus at neutron resonance energies. Demonstration measurements by using a lithium-glass pixel type scintillator and a gas electron multiplication (GEM) neutron detector were carried out at NOBORU beam line in MLF/J-PARC for sodium, manganese, cobalt, copper, zinc, molybdenum, cadmium, indium, tantalum and gold. To discuss advantages of the resonance absorption radiography the mass attenuation coefficient at resonance energy of each element was compared to that at 25 meV. In addition a visibility index derived by a resonance peak cross section and a relative width (full width at half maximum divided by its resonance energy) was proposed to summarize visibility of the neutron resonance absorption radiography for natural elements. The values of visibility index and the resonance energy indicated that large advantages of the resonance absorption radiography were obtainable for the following elements: sodium (Na), manganese (Mn), cobalt (Co), rhodium (Rh), silver (Ag), cadmium (Cd), indium (In), xenon (Xe), cesium (Cs), samarium (Sm), europium (Eu), dysprosium (Dy), erbium (Er), thulium (Tm), hafnium (Hf), tantalum (Ta), tungsten (W), rhenium (Re), iridium (Ir) and gold (Au). (C) 2013 The Authors. Published by Elsevier B.V.
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