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A high position resolution neutron detector for time-of-flight measurements is being developed to measure the ( p , p n ) reaction in inverse kinematics with an excitation energy resolution of 1 MeV at the RIKEN RI Beam Factory. In this study, a new method based on the segmentation of the neutron detector part is employed to achieve a position resolution on the order of mm with a prototype neutron detector. The prototype detector consists of 8 × 8 scintillating fibers, two multi-anode photomultiplier tubes (PMTs) and two light guides. The scintillating fibers have a cross sectional area of 3 . 75 × 3 . 75 mm 2 . The prototype’s performance is studied using the neutron and proton beams provided at the Cyclotron and Radioisotope Center (CYRIC), Tohoku University and the Research Center for Nuclear Physics (RCNP), Osaka University. It is confirmed that the hit pattern analysis correctly recognizes the neutron detection position within the fiber size of 3.75 mm. The obtained TOF resolution of 350 ps (FWHM), lateral position resolution of 2.5 mm (FWHM), and longitudinal position resolution of 50–60 mm (FWHM) satisfy the requirements to achieve an excitation energy resolution of 1 MeV. The typical detection efficiency is ∼ 2.0% for a neutron with a kinetic energy of 50–200 MeV. The detailed investigation of the detection efficiency in conjunction with the neutron hit position reveals the existence of the non-uniformity of the efficiency. It is shown that the non-uniformity can be mitigated by reducing the threshold level, and by increasing the detector size. For a larger neutron detector, based on the design of the prototype detector, the non-uniformity will thus be negligible.

An examination of the structural integrity and defects of a fabricated mercury target vessel for Japan Proton Accelerator Research Complex (J-PARC) spallation neutron source is presented. Ultrasonic testing (UT) and radiographic testing (RT) were employed as nondestructive inspection methods. The mercury target vessel is composed of SUS316L stainless steel and was designed with multi-walled structures consisting of double-guard vessels with thin walls of 3-mm thickness and assembled by tungsten inert gas welding. The mercury target vessel has complex characteristic, and the weld defect for the thin walls is often very difficult to detect using conventional UT techniques. To overcome this barrier, we employed two new UT techniques, namely 1) immersion ultrasonic with a 50-MHz ultrasonic probe and 2) phased arrays ultrasonic with the full matrix capture (FMC) and the total focusing method (TFM). The examination revealed the formation of small defects and cracks wherein the wall thickness was less than 6 mm. Therefore, new UT techniques are useful for evaluating the structural integrity and defects of the new fabricated mercury vessels. The design and the fabrication process of the mercury target vessel was also evaluated and improved in this study. The use of wire electric discharge machining (EDM) in the fabrication process is desirable to reduce the amount of welding and subsequent welding deformation. The roughness and chemical compositions of the processed surface layer by wire EDM were also examined. The oxide layer was perfectly removed by two-step chemical polishing, and the chemical composition of the layer was analyzed using energy dispersive X-ray spectrometry. In addition, the surface roughness was reduced after polishing to enhance fatigue life and minimize internal defects caused by welding.

The spallation neutron source at the Japan Proton Accelerator Research Complex (J-PARC) mercury target vessel is used for various materials science studies, work is underway to achieve stable operation at 1 MW. This is very important for enhancing the structural integrity and durability of the target vessel, which is being developed for 1 MW operation. In the present study, to reduce thermal stress and relax stress concentrations more effectively in the existing target vessel in J-PARC, an optimization approach called the Taguchi method (TM) is applied to thermo-mechanical analysis. The ribs and their relative parameters, as well as the thickness of the mercury vessel and shrouds, were selected as important design parameters for this investigation. According to the analytical results of 18 model types designed using the TM, the optimal design was determined. It is characterized by discrete ribs and a thicker vessel wall than the current design. The maximum thermal stresses in the mercury vessel and the outer shroud were reduced by 14% and 15%, respectively. Furthermore, it was indicated that variations in rib width, left/right rib intervals, and shroud thickness could influence the maximum thermal stress performance. It is therefore concluded that the TM was useful for optimizing the structure of the target vessel and to reduce the thermal stress in a small number of calculation cases.

Activation cross-sections for the natW(d,x)181,182 m,182 g,183,184m,184g,184g(cum),186gRe, 187W and 182g+m+nTa nuclear reactions were measured from the respective thresholds up to 38 MeV by using a stacked-foil activation technique combined with HPGe γ-ray spectrometry. The results are compared with the available literature data and theoretical data extracted from the TENDL-2015 library, and found only a partial agreement among them. Independent cross-sections for the natW(d,x)182g+m+nTa reactions are reported here for the first time. Physical thick target yields for the investigated reaction products were deduced from the measured cross-sections and compared with the directly measured yields found in the literature. The deduced yield curves indicate that a typical irradiation of an enriched 186W target with 100 µA current from a low energy (

Mercury target vessel in the JSNS, which is made of 316L SS, is damaged owing to the pressure wave-induced cavitation resulting from the proton beam bombardment. The cavitation damage decreases the structural integrity of the target vessel and is currently a dominant factor to decide the service life in compared with the radiation damage. Injecting microbubbles into mercury is one of the prospective techniques to mitigate the pressure waves and cavitation damage. In the JSNS, a microbubble generator with a gas circulation system was installed and has been operated since October 2012. The effects of microbubble injection into mercury on pressure wave mitigation were studied using a laser Doppler vibrometer. The result showed that the vibrational velocity of the target vessel is clearly reduced according to the increase of void fraction. An average peak vibrational velocity under 340 kW operation with the void fraction of 0.1\% was reduced to 1/4 of that without injecting microbubbles., J-PARCの核破砕中性子源(JSNS)水銀ターゲット容器は、陽子線入射励起圧力波により励起されるキャビテーションによる損傷を受ける。キャビテーションによる損傷は、容器の構造健全性を低下させるため現在のところ容器の交換寿命を決める支配因子となっている。圧力波及びキャビテーションによる損傷を低減するためには、水銀中にガスマイクロバブルを注入することが効果的な手法である。JSNSでは、ガスマイクロバブルを注入するためのシステムを2012年10月に設置し、レーザードップラー振動計を用いて容器の振動をモニタリングすることによって水銀中へのバブル注入の効果をした。その結果、振動速度は気泡注入量の増加に伴って減少することを確認した。また長期間の運転では、気泡注入によって平均でバブル注入無しの1/4程度の振動速度を維持した。

The liquid mercury target system for the Japan Spallation Neutron Source (JSNS) began operating in May 2008. A mercury target vessel composed of type 316L stainless steel suffers radiation damage in the proton and neutron environment. In addition to this damage, the inner wall of the target vessel in contact with mercury is damaged by cavitation-induced erosion, which is caused by rarefied pressure waves. The target vessel was replaced with a new target in November 2011, because the pneumatic bellow type flange was damaged during the Great East Japan Earthquake, that occurred on March 11, 2011. Before replacing the target, 50 mm diameter disk specimens were cut from the beam window of the target vessel in order to investigate the cavitation damage inside the target vessel and to evaluate the change in the mechanical properties due to radiation damage. A video camera was used to inspect the inside of the target vessel and no flow induced erosion damage was detected on the flow guide by visual inspection. Cavitation damage from the proton pulse was concentrated at the center and approximately 15 mm from the center of the beam window. In addition, the depth of the cavitation damage was quantitatively measured using a laser profilometer and a metallurgical surface replica. Based on the detailed measurements, it was concluded that the eroded damage depth of the beam window was 250 μm after 475 MW h of operation.

The ion-production efficiency of a newly developed singly charged ion source (SCIS) has been investigated to discuss the possibility of it being used in an isotope separation on-line system that provides 11C ions for heavy-ion cancer therapy with simultaneous verification of the irradiation field using positron emission tomography. The SCIS uses a low-energy hollow electron beam to produce singly charged carbon ions efficiently. To deliver sufficient 11C ions to the treatment room from a limited amount of 11C molecules, which are produced from a boron compound target and proton-beam irradiation via the 11B(p,n)11C reaction, the SCIS must have high ion-production efficiency. To realize this high efficiency, the SCIS was designed using a three-dimensional particle-in-cell code in previous work. With the fabricated SCIS, we performed experiments to measure the efficiency of producing CO+2 ions from nonradioactive 12CO2 molecules and C+ ions from nonradioactive 12CH4 molecules. We found that the SCIS achieved efficiencies of εC+=4×10−3 (0.4%) for C+ production and εCO+2=0.107 (10.7%) for CO+2 production.

When an intense pulsed proton beam with a power of 1 MW is irradiated to a mercury target, a pressure wave caused by the proton beam gives a vibration on the target vessel. Pitting damage also occurs on the target vessel, especially incident beam area, resulting in shortening of a life-time. It is very important to monitor the vibration of the target vessel from the view point of the life-time estimation. We developed the target vessel diagnosis system using laser Doppler method and successfully installed it in an actual pulsed spallation source. The diagnosis system consists of retro-reflecting corner-cube mirror (reflective mirror) on the target, mirror assembly in a reflector plug and laser source-detector. The newly developed reflective mirror, made by nickel, was installed by vacuum silver brazing on the target vessel to detect the target vibration. In order to pass the laser beam to the target vessel, a mirror assembly was installed inside the reflector plug. It is replaceable using a remote handling machine during a maintenance period. Nd-YAG laser beam (wave length: 533 nm) with the power of 50 mW was adopted to detect the target vibration. The first proton beam to the target in the spallation neutron source (JSNS) was provided on 30 May 2008. The first signal related to the target vibration was also detected by using this target vessel diagnosis system.

A liquid mercury target system for the MW-class pulsed spallation neutron source is installed at the Materials and Life science experimental Facility (MLF) of J-PARC. MW-class proton bombardment of the mercury brings about intensive pressure waves that impact on mercury target vessel repeatedly at 25 Hz and can remarkably degrade the structural integrity and the lifetime of the vessel. In order to realize the high-power mercury target, R&D on the pressure wave mitigation technology is carried out experimentally and theoretically. One of the promising methods to mitigate the pressure waves is to inject microbubbles into the mercury. The microbubbles exhibit three effects for the mitigation: absorption, attenuation and suppression. An in-situ diagnostic system for measuring the dynamic responses induced by the pressure waves is installed in the Japan Spallation Neutron Source (JSNS). In this paper, we briefly describe the strategy to realize the high-power mercury target in the JSNS.

Target vessel wall being damaged by pitting caused by pressure waves generated when pulsed high-power beams are injected is a crucial issue in the realization of a pulsed high-power mercury target for spallation neutron sources. The injection of micro-bubbles into mercury is a prospective technology for use in mitigating the pressure wave and the resulting pitting. The bubble flow field in an actual target vessel was numerically examined and the optimal conditions for bubble injection were investigated. The results indicated the possibility of the bubbles being distributed over the core regions when they are injected in the appropriate position according to their diameter.

We have constructed a polarized proton solid target system for radioactive nuclear beam experiments at the Center for Nuclear Study, the University of Tokyo. The proton polarization is based on an electron population difference in a photo-excited triplet state of pentacene molecule. The target system was completed in 2003 and applied to a RI beam experiment in 2003 and 2005 by using the projectile fragment separator, RIPS at RIKEN. The maximum polarization reached 20% under the condition of T=100 K and B=0.09 T. Overview of the polarized target and its application in physics experiments at RIPS and RIBF of RIKEN are presented.

A new high-energy beam polarimeter is proposed for Nuclotron, which uses the Internal Target Station (ITS). This polarimeter based on a measurement of asymmetry for the d–p elastic scattering will allow one to measure simultaneously both vector and tensor components of deuteron beam polarization. For this purpose an analyzing powers measurement for the d–p elastic scattering at energies T d = 0.88–2 GeV is proposed. The precise measurements of the deuteron analyzing powers over the energy range T d = 300–2000 MeV can give an irreplaceable clue to the study of the spin dependence of three nucleon forces.

A liquid mercury target system for the MW-class pulse spallation neutron source is being developed in the world. Failure probability analysis on the mercury target that will be installed at the material and life science facility in J-PARC was carried out as taking into account the repeatedly loading by pressure waves and material degradation due to pitting and neutron irradiation damages. It was quantitatively evaluated that the failure probability of the safety hull in the target is lower than 10 −11 throughout the expected lifetime in design. On the other hand, the failure probability of the mercury vessel directly subject to the pressure waves and the pitting damage increases gradually with proton-beam power and gets to be ca. 99.9% in MW-class target lifetime expected in the design.

Interfacial fracture of thermally stressed layered composites is often characterized by application of a mechanical load. Here a novel mechanical testing method was applied to study the delamination of thermal barrier composites. With a geometry similar to the double cantilever beam compressive loading was transferred into tensile stress normal to the average location of the interfaces. As-sprayed and annealed composites were tested. Fracture relevant microstructural changes and crack growth in the top coat and at the interface between bond coat and top coat were monitored using scanning electron microscopy. The local strain situation was determined via the analysis of the image contrast. Finite element modeling was used to illustrate the effect of the interface roughness on the failure origin. Similar as reported in literature for thermal loading, mechanical loading of a rough interface causes high stresses in interfacial roughness peaks and valleys. However, contrary to thermal loading, the position of the maximum in tensile and compressive stress is independent of the existence of a thermally grown oxide. Implications for the mechanical and thermo-mechanical testing of layered composites are discussed.

The strain dependency of the stiffness of bonded and free-standing thermal barrier coatings (TBCs) was analyzed using four point bending. The deformation in top and side face of the material was observed in-situ using optical and scanning electron microscopy. For free-standing TBCs, the strain of the tensile part above the neutral bending axis was larger than on the compressive part. Furthermore, the ratio of strain of tensile to compressive part increased with increasing applied strain and the position of the neutral axis sifted further to compressive side. The stiffness for free-standing TBC changed from 8 to 17 GPa with applied strain. For bonded TBCs, the average stiffness under tensile or compressive bending was determined considering residual stresses. The stiffness of the bonded TBCs increased from 12 to 38 GPa as the applied strain was increased from − 0.75 to 0.11%. This strong strain dependency of the TBC stiffness can be associated with the large number of micro-cracks and pores. Finally, a unifying stress–strain curve is presented for strains from − 0.75 to 0.23% obtained using results of the free-standing and bonded TBC.

Thin solid oxide fuel cells (SOFCs), with a planar multi-layer structure, typically exhibit curvature behavior and develop residual stresses originating from the thermal mismatch of the materials involved. The curvature effects oppose successful stack operation, which also relies on the permanent physical contact of geometrically stable planar cells. Curvature studies have been carried out as part of the project “Component Reliability in Solid Oxide Fuel Cell Systems for Commercial Operation” (CORE-SOFC). Various aspects of the curvature of unconstrained cells and cells fixed in stacks were considered. The experiments and theoretical analyses included the curvature changes due to anode reduction and the suppression of cell curvature, either by a compensation layer or by an additional surface load. The critical stresses in the layers are addressed and results are reported for different cell thicknesses and lengths. Cell flatness can be achieved with a compensation layer but the average residual tensile stress in the anode increases. On the other hand finite element analysis (FEA) indicates that relatively high loads are necessary to completely suppress cell curvature. Furthermore, analytical and FEA results on the curvature changes of sealed cells during cooling are presented and the impact of variations in sealing geometry is illustrated. The results are compared to in-situ observations of model stacks, where curvature and strain are analyzed using image correlation.

We have constructed a new type of spin polarized solid proton target which can be operated under a low magnetic field of 0.08T and a high temperature of 100 K. We have measured for the first time the polarization asymmetry of an unstable beam of 6He at an energy of 71 MeV/u. Optical potential analyses have been carried out.

The stiffness of air plasma sprayed (APS) thermal barrier coatings (TBCs) was determined from bending experiments combining strain analysis on a microstructural level with macroscopic mechanical parameters. Tests were performed with freestanding and attached TBCs, the latter either loaded in tension or in compression. Relationships are derived, which describe the TBC stiffness in a multilayer composite (attached TBC) and for a bimodular material that possess a lower stiffness in tension than in compression (stand-alone TBC). The increase of in-plane stiffness with increasing compressive stress emphasizes the importance of the spraying defects for the elastic response of the coating.

Protons in a crystal of naphthalene doped with pentacene have been polarized to 37% in a magnetic field of 0.3 T and at a temperature of 100 K . In order to improve the proton polarization further, a study to find an optimal condition for polarizing protons has been carried out by using a proton polarizing system with a cylindrical microwave cavity. As a part of the study, the dependencies of the polarization rate at an early stage of the build-up and of the relaxation rate during laser irradiation on the operation current of the laser have been measured.

A polarized proton solid target has been developed at the Center for Nuclear Study, the University of Tokyo. The polarized target makes use of a large population difference among Zeeman sub-levels in the photo-excited triplet state of pentacene. We have successfully applied this polarized target to the first RI beam experiment, where a vector analyzing power for the proton- 6 He elastic scattering has been measured.

An ohmic-heating laser ion source with a thin ionizer of thickness of 30 μm has been developed for the TIARA-ISOL. It can form an electric field of 4–5 V/cm inside the ionizer. The properties of the laser ion source were tested on- and off-line with aluminum isotopes. The FWHM of the time distribution of the bunched photoions from the ion source was about 4 μs for 27Al. In on-line experiment, a photoionization efficiency of about 0.1% for 25Al was obtained.

A permanent magnet rotating type induction pump (PM pump) was developed to provide mercury to a liquid mercury target system in Japan Spallation Neutron Source (JSNS). Mechanical pumps, such as a gear pump and a centrifugal pump, have risk of leakage of mercury from the seal parts. Induction pumps can avoid mercury leakage because they have no seal parts. The PM pump could be compact compared with a conventional induction pump; however, power loss must be reduced to avoid overheating of the system. Then optimizations for the thickness of mercury duct wall and width of the duct were carried out to reduce heat loss due to the eddy current in the duct generated by the induction, and to reduce flow-induced loss. As for the flow-induced loss, backflow would occur at the outside of the duct because of the difference in the Lorentz force between inside and outside of the duct. Consequently, the developed PM pump could have sufficient performance for the target system in JSNS and operate with low vibration.

A high‐resolution laser spectroscopy system for refractory elements with an argon‐ion‐ sputtering atomic beam source was constructed, and it has been demonstrated that the sputtering method is extremely useful as an atomic beam source for high‐resolution laser spectroscopy to measure hyperfine structures and isotope shifts for refractory elements, such as Hf, Ta, and W. This source produced intense neutral atomic beams of more than 1010 atoms/s for these elements, and the yield was easily controlled by adjusting the argon‐ion current and the acceleration voltage. Resonance linewidths were 32, 66, and 48 MHz for Hf, Ta, and W, respectively, which are sufficient to measure the hyperfine structures and the isotope shifts in optical transitions. With this system, the signal‐to‐noise ratio reached more than 106. In addition, the temperature of the sputtered atoms found was rather low compared to the kinetic energy given to the atoms.

A non-linear ultrasonic method was applied for evaluating the cavitation damage, so-called pitting damage, in the mercury target of the Japan Spallation Neutron Source (JSNS). First, pitting damage was imposed on disk specimens in mercury using the magnetic impact testing machine (MIMTM) with various numbers of impacts (0, 104, 105, 106, 107 and 108). The pitting damage was imaged with resonance and non-resonance modes, respectively, by employing a non-linear acoustic imaging system. Waveform attenuation and generation of higher harmonics, which have high relevance to the degree of pitting damage, were useful for the imaging. Combined with the attenuation phenomenon, the resonance mode imaged the micropits with higher harmonics more effectively with higher harmonics, compared with the non-resonance mode.