J-PARC Research Articles

Polarization analysis for small-angle neutron scattering with a 3He spin filter at a pulsed neutron source

Neutron polarization analysis (NPA) for small-angle neutron scattering (SANS) experiments using a pulsed neutron source was successfully achieved by applying a 3He spin filter as a spin analyzer for the neutrons scattered from the sample. The cell of the 3He spin filter gives a weak small-angle scattering intensity (background) and covers a sufficient solid angle for performing SANS experiments. The relaxation time of the 3He polarization is sufficient for continuous use for approximately 2 days, thus reaching the typical duration required for a complete set of SANS experiments. Although accurate evaluation of the incoherent neutron scattering, which is predominantly attributable to the extremely large incoherent scattering cross section of hydrogen atoms in samples, is difficult using calculations based on the sample elemental composition, the developed NPA approach with consideration of the influence of multiple neutron scattering enabled reliable decomposition of the SANS intensity distribution into the coherent and incoherent scattering components. To date, NPA has not been well established as a standard technique for SANS experiments at pulsed neutron sources such as the Japan Proton Accelerator Research Complex (J-PARC) and the US Spallation Neutron Source. It is anticipated that this work will contribute significantly to the accurate determination of the coherent neutron scattering component for scatterers in various types of organic sample systems in SANS experiments at J-PARC, particularly for systems involving competition between the coherent and incoherent scattering intensity.

Development of negative muonium ion source for muon acceleration

A negative muonium ion (${\mathrm{Mu}}^{\ensuremath{-}}$) source using an aluminum foil target (Al target) was developed as a low-energy muon source. ${\mathrm{Mu}}^{\ensuremath{-}}$ ions are produced by irradiating the Al target with a 3-MeV positive muon (${\ensuremath{\mu}}^{+}$) beam and observed using a microchannel plate. An experiment to produce ${\mathrm{Mu}}^{\ensuremath{-}}$ ions was conducted to evaluate the performance of this ${\mathrm{Mu}}^{\ensuremath{-}}$ ion source. The measured event rate of ${\mathrm{Mu}}^{\ensuremath{-}}$ ions was $(1.7\ifmmode\pm\else\textpm\fi{}0.3)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}\text{ }\text{ }{\mathrm{Mu}}^{\ensuremath{-}}/\mathrm{s}$ when the event rate of the incident ${\ensuremath{\mu}}^{+}$ beam was $1.3\ifmmode\times\else\texttimes\fi{}{10}^{6}/\mathrm{s}$. The experiment was conducted at the Muon Science Establishment, D-line in the Materials and Life Science Experimental Facility within the Japan Proton Accelerator Research Complex. The formation probability, defined as the ratio of the ${\mathrm{Mu}}^{\ensuremath{-}}$ ions to the incident muons on the Al target, was $(1.1\ifmmode\pm\else\textpm\fi{}0.2(\mathrm{stat}{)}_{+0.1}^{\ensuremath{-}0.0}(\mathrm{syst}))\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}$. This ${\mathrm{Mu}}^{\ensuremath{-}}$ ion source was first adopted in the commissioning of the muon accelerator at the D-line, and the event rate of the accelerated ${\mathrm{Mu}}^{\ensuremath{-}}$ ions was consistent with the expectation. This ${\mathrm{Mu}}^{\ensuremath{-}}$ ion source boosted the development of the muon accelerator, and the practicality of this low-energy muon source obtained using a relatively simple apparatus was demonstrated.

Dynamical Response of Transition-Edge Sensor Microcalorimeters to a Pulsed Charged-Particle Beam

A superconducting transition-edge sensor (TES) microcalorimeter is an ideal X-ray detector for experiments at accelerator facilities because of good energy resolution and high efficiency. To study the performance of the TES detector with a high-intensity pulsed charged-particle beam, we measured X-ray spectra with a pulsed muon beam at the Japan Proton Accelerator Research Complex (J-PARC) in Japan. We found substantial temporal shifts of the X-ray energy correlated with the arrival time of the pulsed muon beam, which was reasonably explained by pulse pileup due to the incidence of energetic particles from the initial pulsed beam.

Commissioning of the next-generation LLRF control system for the Rapid Cycling Synchrotron of the Japan Proton Accelerator Research Complex

The low level rf (LLRF) control system has key roles for the stable acceleration of the high intensity beam. The original LLRF control system for the Rapid Cycling Synchrotron (RCS) of the Japan Proton Accelerator Research Complex (J-PARC) has been working nicely without major issues for more than ten years since the operation of the RCS started in 2007. Due to the obsolescence of the key digital devices, it is difficult to maintain the original system for a longer period, therefore we developed the next-generation LLRF control system based on the MTCA.4. All of the LLRF functions of the new system were tested and commissioned. In this article, we describe the commissioning of two key functions, the phase feedback to damp the longitudinal dipole oscillation and the multiharmonic vector rf voltage control feedback for twelve cavities. The commissioning methodologies and beam test results are presented. The stable acceleration of the high intensity beam at the design intensity of 8.3×1013 ppp is achieved. The next-generation LLRF control system has been successfully deployed and commissioned. This article is a follow-up of our previous articles, IEEE Transactions on Nuclear Science, 66 (7), pp. 1242-1248 (2019) and Phys. Rev. Accel. Beams 22, 092001 (2019).

Development of a multiwire proportional chamber with good tolerance to burst hits

The DeeMe experiment to search for muon-to-electron conversions with a sensitivity 10–100 times better than those achieved by previous experiments is in preparation at the Japan Proton Accelerator Research Complex. The magnetic spectrometer used by the DeeMe experiment consists of an electromagnet and four multiwire proportional chambers (MWPCs). The newly developed MWPCs are operated with a high voltage (HV) switching technique and have good burst-hit tolerance. In this article, the final designs of the MWPCs, amplifiers for readout, and HV switching modules are described. Additionally, some results of MWPC performance evaluation are presented.

Measurement of γ rays from 6LiF tile as an inner wall of a neutron-decay detector

A neutron lifetime measurement conducted at the Japan Proton Accelerator Research Complex (J-PARC) is counting the number of electrons from neutron decays with a time projection chamber (TPC). The γ rays produced in the TPC cause irreducible background events. To achieve the precise measurement, the inner walls of the TPC consist of 6Li-enriched lithium-fluoride (6LiF) tiles to suppress the amount of γ rays. In order to estimate the amount of γ rays from the 6LiF tile, prompt gamma ray analysis (PGA) measurements were performed using germanium detectors. We reconstructed the measured γ-ray energy spectrum using a Monte Carlo simulation with the stripping method. Comparing the measured spectrum with a simulated one, the number of γ rays emitted from the6LiF tile was (2.3+0.7−0.3) × 10−4 per incident neutron. This is 1.4+0.5−0.2 times the value assumed for a mole fraction of the 6LiF tile. We concluded that the amount of γ rays produced from the 6LiF tile is not more twice the originally assumed value.

Neutron capture cross sections of curium isotopes measured with ANNRI at J-PARC

ABSTRACT The neutron capture cross sections of and were measured for the neutron energy range of 1–1000 eV via the neutron time-of-flight method with Accurate Neutron-Nucleus Reaction measurement Instrument (ANNRI) at Materials and Life Science Experimental Facility (MLF) of the Japan Proton Accelerator Research Complex (J-PARC). The world’s most intense neutron pulses from the Japan Spallation Neutron Source (JSNS) enable the accurate measurement of neutron capture cross sections. Besides, single-bunched neutron pulses allow the analysis in a higher neutron energy region than the previous measurement at ANNRI. The resonance analyses were performed up to 1000 eV by using a resonance shape analysis code REFIT. The spectra of prompt gamma-rays from neutron capture reactions of and were also obtained, and 43 and 10 prompt gamma-ray peaks from () and () reactions were newly observed, respectively.

MEASUREMENT, EVALUATION AND VALIDATION OF MOLYBDENUM CROSS SECTIONS

Available nuclear data for molybdenum included in the nuclear data libraries are not of sufficient quality for reactor physics or criticality safety issues and indeed information about uncertainties and covariance is either missing or leaves much to be desired. Therefore, IRSN and JAEA performed experimental measurements on molybdenum at the J-PARC (Japan Proton Accelerator Research Complex) facility in Japan. The aim was to measure capture cross section and transmission of natural molybdenum at the ANNRI (Accurate Neutron-Nucleus Reaction measurement Instrument) in the MLF (Material Life and science Facility) of J-PARC. The measurements were performed on metallic natural molybdenum samples with various thicknesses. A NaI detector, placed at a flight-path length of about 28 m, was used for capture measurements and a Li-glass detector (flight-path length of about 28.7 m) for transmission measurements. Following the data reduction process, the measured data are being analyzed and evaluated to produce more accurate cross sections and associated uncertainties.

Low-power proton beam extraction by the bright continuous laser using the 3-MeV negative-hydrogen linac in Japan Proton Accelerator Research Complex

ABSTRACT The Japan Atomic Energy Agency (JAEA) has designed a Transmutation Physics Experimental Facility (TEF-P) as an experimental facility in the Japan Proton Accelerator Research Complex (J-PARC). The TEF-P is a critical assembly driven by a low-power proton beam, a maximum of 10 W, which is extracted from a high-power beam source, such as 250 kW of 400 MeV proton beam of the J-PARC linac. To extract such a low-power proton beam from the high-power proton beam, we developed a laser charge exchange (LCE) device and employed its technique, which is one of the non-contact beam extraction techniques. To confirm the performance of the LCE device, a low-power proton beam was extracted using a negative-hydrogen linac having an energy of 3 MeV, and a bright continuous laser. A 0.57 mW proton beam was successfully extracted with a laser stripping efficiency of . These values obtained are in good agreement with the estimated values.

Position distribution calculation of annihilation radiations and bremsstrahlung x rays in water during irradiation of positive muons: a Monte Carlo simulation study

Range, momentum and deviation of momentum determinations of muons are important for quality assessment (QA) of beams. Imaging of annihilation radiations emitted from positrons decayed from positive muons and that of bremsstrahlung x-rays emitted from positrons and secondary electrons from positive muons are possible methods of imaging muons. However, the energies and intensities as well as position distributions of these radiations have not been obvious. Thus we calculated the energy spectrum and the distributions of annihilation radiations as well as bremsstrahlung x-rays produced in water during irradiation of positive muons using Monte Carlo simulation. The calculations were conducted for 84.5 MeV /c positive muons, which is the same beam condition used in an experimental facility at the Japan Proton Accelerator Research Complex (J-PARC). We were able to calculate the energy spectrum as well as the position distributions of annihilation radiations and bremsstrahlung x-rays. The energy spectrum showed a broad distribution of bremsstrahlung x-rays, mainly from decayed positrons with an energy range up to 50 MeV with higher intensity in low-energy bremsstrahlung x-rays. The spectrum also showed a sharp peak at 511-keV from annihilation radiations. The position distribution of annihilation radiations was wider than those of the bremsstrahlung x-rays. The position distribution of the bremsstrahlung x-rays were nearly identical to the Cerenkov-light position distribution emitted by the decayed positrons in water. We conclude that imaging of bremsstrahlung x-rays from decayed positrons by using an x-ray camera is a promising method for the QA of positive muons and that higher spatial resolution images of positron distributions will be measured than those measured by annihilation radiations.

Neutron lifetime measurement with pulsed cold neutrons

Abstract The neutron lifetime has been measured by comparing the decay rate with the reaction rate of $^3$He nuclei of a pulsed neutron beam from the spallation neutron source at the Japan Proton Accelerator Research Complex (J-PARC). The decay rate and the reaction rate were determined by simultaneously detecting electrons from the neutron decay and protons from the $^3$He(n,p)$^3$H reaction using a gas chamber, the working gas of which contains diluted $^3$He. The measured neutron lifetime was $898\,\pm\,10\,_{\rm stat}\,^{+15}_{-18}\,_{\rm sys}\,$s.

Neutron diffraction experiment with the Y116S variant of transthyretin using iBIX at J-PARC: application of a new integration method.

Transthyretin (TTR) is one of more than 30 amyloidogenic proteins, and the amyloid fibrils found in patients afflicted with ATTR amyloidosis are composed of this protein. Wild-type TTR amyloids accumulate in the heart in senile systemic amyloidosis (SSA). ATTR amyloidosis occurs at a much younger age than SSA, and the affected individuals carry a TTR mutant. The naturally occurring amyloidogenic Y116S TTR variant forms more amyloid fibrils than wild-type TTR. Thus, the Y116S mutation reduces the stability of the TTR structure. A neutron diffraction experiment on Y116S TTR was performed to elucidate the mechanism of the changes in structural stability between Y116S variant and wild-type TTR through structural comparison. Large crystals of the Y116S variant were grown under optimal crystallization conditions, and a single 2.4 mm3 crystal was ultimately obtained. This crystal was subjected to time-of-flight (TOF) neutron diffraction using the IBARAKI biological crystal diffractometer (iBIX) at the Japan Proton Accelerator Research Complex, Tokai, Japan (J-PARC). A full data set for neutron structure analysis was obtained in 14 days at an operational accelerator power of 500 kW. A new integration method was developed and showed improved data statistics; the new method was applied to the reduction of the TOF diffraction data from the Y116S variant. Data reduction was completed and the integrated intensities of the Bragg reflections were obtained at 1.9 Å resolution for structure refinement. Moreover, X-ray diffraction data at 1.4 Å resolution were obtained for joint neutron-X-ray refinement.

Energy resolution and neutron flux of the 4SEASONS spectrometer revisited

The elastic energy resolution, integrated intensity, and peak intensity of the direct-geometry neutron chopper spectrometer 4SEASONS at Japan Proton Accelerator Research Complex (J-PARC) were re-investigated. This was done with respect to the incident energy and the rotation speed of the Fermi chopper using incoherent scattering of vanadium and simple analytical formulas. The model calculations reproduced the observed values satisfactorily. The present work should be useful for estimating in instrument performance in experiments.

Measurement of thick target neutron yield at 180°for a mercury target induced by 3-GeV protons

A thick target neutron yield (TTNY) for a mercury target at an angle of 180°from the incident beam direction was measured with the time-of-flight method using a 3-GeV proton beam at the Japan Proton Accelerator Research Complex (J-PARC). Comparison of the experimental results with a Monte Carlo particle transport simulation by the Particle and Heavy Ion Transport code System (PHITS) shows that the default spallation model of PHITS, the Liège intranuclear cascade model version 4.6 coupled with the generalized evaporation model (INCL4.6/GEM) reproduces the measured TTNY fairly well, whereas apparent overestimation is observed for the former default model, the Bertini intranuclear cascade model coupled with GEM (Bertini/GEM). These trends are consistent with the experimental results of neutron-induced reaction rates obtained using indium and niobium activation foils.

Gas-flow humidity control system for neutron reflectivity measurements.

We developed a novel humidity control system for neutron reflectivity measurements based on the two-way gas-flow method that can generate up to 85% relative humidity (RH) within a temperature range of 5 °C-85 °C. The system consists of a gas-flow-type humidity generator and a thermostatic sample chamber, each of which can independently control the temperature. The key features include rapid humidity response and long stable operation time. The humidity reaches equilibrium within 2 to 5 min during the humidity change, and the system exhibited acceptable stability over a three-day, nonstop experimental measurement duration, with a precision of ±1% RH at 85 °C and 85% RH. The sample chamber is capable of measuring substrate samples with dimensions of up to 2-in. in diameter and 5-mm in thickness. We demonstrate the reflectivity data measured at a pulsed neutron facility, MLF BL17, in the Japan Proton Accelerator Research Complex. The combined use of this system with neutrons permits in situ, time-resolved studies of the swelling process of polyvinyl alcohol and adhesive materials.

Development of an in Situ 3He NSF Using SEOP Technique with an Evaluation System for the Pulsed Neutron Source

A 3He spin filter is a useful device for polarizing a neutron beam. We are developing the 3He spin filters for users of the material and life science facility of the Japan Proton Accelerator Research Complex (J‑PARC). An in situ SEOP system with a 3He polarization evaluation system using nuclear magnetic resonance (NMR) method of adiabatic fast passage and electron paramagnetic resonance (EPR) was developed. We conducted an experiment on the neutron beam line BL10 (NOBORU) of J-PARC to confirm the consistency of 3He polarization, estimated using the neutron transmission, NMR and EPR. The polarization of 3He, evaluated using the different methods, was consistent and the evaluation system operated normally for about 6 h.

The Large-Area Detector for Small-Angle Neutron Scattering on iMATERIA at J-PARC

An area detector with a central hole structure was built up for small-angle neutron scattering (SANS) on the iMATERIA instrument at Japan Proton Accelerator Research Complex (J-PARC). Linear position-sensitive detector tubes filled with 3He gas were arranged in three layers leaving a central hole. As a result of the calibration process, a SANS measurement with wide q-range from 0.007 Å−1 to 4.3 Å−1 was achieved in double-frame operation, supplying neutrons with wavelengths from 1 Å to 10 Å. As a merit of this central hole structure, neutron transmission can be measured simultaneously to reduce experimental time and effort. This is ideal for time-resolved studies, in which the sample transmission can be time-dependent, throughout the whole experiment. Additionally, the data storage system in ‘event mode’ format provides an excellent platform for such time-resolved experiments.

Interfacial Analysis of Plasma Fusion Bonded Interfaces Under Various Bonding Conditions by Neutron Reflectometry

Wafer bonding is one of the key technologies for the 3D integrations, and 300-mm-wafer-level bonding is applied for image sensors, memories, and so on. Fusion bonding using plasma activation as wafer-level bonding process for such devices should require high-yield and high-reliabilities, therefore the interfacial analyses are significant. There are several interfacial analyses for bonded interfaces such as scanning acoustic microscopy (SAM), TEM and so on. These methods are indispensable in the evaluation of the bonded interfaces, therefore, the specimens would be affected by the measurement preparations or circumstances. Generally, SAT images of the interface of the bonded wafers show voids among the interface caused by redundant hydrophilization, and interfacial structure can be observed by cross-sectional TEM. However, the cross-sectional TEM image of the interfacial structure of dioxide was difficult to analyze, because the contrast of the reacted (or water contained) layer is very weak. As the reaction occurs at the interface of substrates and analyzing targets are light elements (H2O, -OH) and other deuterated substitutes. Therefore, in previous study, we demonstrated the interfacial analysis of wafer-level bonded dioxide wafers by neutron reflectivity (NR), and we confirmed that NR would have possibilities to distinguish conditions of bonded interfaces.[1] In this research, 300 mm Si wafers are prepared and they are oxidized by wet thermal oxidation at 900ºC and a 100-nm-thick SiO2 layer is deposited. Some of dioxide wafers were polished by chemical mechanical polishing before introduced to a bonding apparatus, and other wafers were introduced as prepared. In the bonding apparatus, first, wafers are activated by plasma, that plasma activation is optimized as a sequential plasma process same as our previous work[2]. Activated wafers are cleaned with megasonic water, then they are transferred and bonded in relatively high vacuum (20 Pa), or are transferred in N2 ambient under atomic pressure and bonded in relatively low vacuum (1000 Pa). These wafers are bonded with a 1000 N load. After that, the bonded wafers are annealed at 200 ºC for 7h in an infrared (IR) image furnace within 3-5 hrs (0 days) or after c.a. 2 days storage in the air. (Table 1)The bonded wafers are evaluated by blade test for bonded strength measurement and NR. NR measurements were performed at BL17 SHARAKU, which is the vertical type time-of-flight neutron reflectometer installed in Japan Proton Accelerator Research Complex (J-PARC). Neutron pulses of 25 Hz are generated with a wavelength band of 0.2 - 0.88 nm. Neutrons penetrate into the bonded interface from the side with incident angles of 0.2º, 0.7º and 1.6º. The obtained NR data was analyzed by Motofit program within the IGOR software package and the analytical program developed for NR data to evaluate neutron scattering length density (SLD) profiles in the film thickness direction of interfacial structures.The results are shown in Table 1. Bonding strength was increased under condition of N2 ambient. And there are a few improvements of bonding strength by storing before post annealing. NR results revealed interfacial structures. Bonded interfaces under low-vacuum conditions have thicker and higher dense interfaces than bonded interfaces under high-vacuum conditions. It seems that the interfacial structures are affected by the bonding circumstances.At the conference, we would like to explain these bonded interfacial structures more precisely with other analyses.[1] M. Fujino, et. al., WaferBond’19, Halle, Germany, Dec. 2019, p.45[2] M. Fujino, et. Al., Jpn. J. Appl. Phys., 59, SBBA02, 2020 Figure 1

Study of muonium emission from laser-ablated silica aerogel

Abstract The emission of muonium ($\mu^+e^-$) atoms into vacuum from silica aerogel with laser ablation on its surface was studied with various ablation structures at room temperature using the subsurface muon beams at TRIUMF and Japan Proton Accelerator Research Complex (J-PARC). Laser ablation was applied to produce holes or grooves with typical dimensions of a few hundred $\mu$m to a few mm, except for some extreme conditions. The measured emission rate tends to be higher for larger fractions of ablation opening and for shallower depths. More than a few ablation structures reach the emission rates similar to the highest achieved in past measurements. The emission rate is found to be stable at least for a couple of days. Measurements of spin precession amplitudes for the produced muonium atoms and remaining muons in a magnetic field determine a muonium formation fraction of $(65.5 \pm 1.8)$%. The precession of the polarized muonium atoms is also observed clearly in vacuum. A projection of the emission rates measured at TRIUMF to the corresponding rates at J-PARC is demonstrated taking the different beam condition into account reasonably.

In Situ Observation for Deformation-Induced Martensite Transformation (DIMT) during Tensile Deformation of 304 Stainless Steel Using Neutron Diffraction. PART I: Mechanical Response

304 stainless steel is one of the most common stainless steels due to its excellent corrosion resistance and mechanical properties. Typically, a good balance between ductility and strength derives from deformation-induced martensite transformation (DIMT), but this mechanism has not been fully explained. In this study, we conducted in situ neutron diffraction measurements during the tensile deformation of commercial 304 stainless steel (at room temperature) by means of a Time-Of-Flight type neutron diffractometer, iMATERIA (BL20), at J-PARC MLF (Japan Proton Accelerator Research Complex, Materials and Life Science Experimental Facility), Japan. The fractions of α′-(BCC) and ε-(HCP) martensite were quantitatively determined by Rietveld-texture analysis, as well as the anisotropic microstrains. The strain hardening behavior corresponded well to the microstrain development in the austenite phase. Hence, the authors concluded that the existence of martensite was not a direct cause of hardening, because the dominant austenite phase strengthened to equivalent values as in the martensite phase. Moreover, the transformation-induced plasticity (TRIP) mechanism in austenitic steels is different from that of low-alloy bainitic TRIP steels.