Publishing type：Research paper (scientific journal)   Publisher：Oxford University Press (OUP)  

Abstract

Nuclear transmutation emerges as a promising approach for reprocessing high-level waste, specifically treating long-lived nuclides like 93Zr from spent fuel. It is essential to accumulate reaction data for these nuclei to advance this prominent treatment and to build a comprehensive understanding of reaction mechanisms. In this study, the residual production cross sections resulting from proton-induced reactions on 93Zr were measured at 27 MeV/nucleon in inverse kinematics. At the RI Beam Factory (RIBF) the OEDO beamline was used to deduce production cross sections for isotopes, 91 − 93Nb, 91, 92Zr, and 88, 89Y. Comparing the results from this study and prior research with calculated excitation functions, a moderate agreement is found with theoretical predictions derived from TALYS and CCONE. The measured cross sections offer valuable insights for future considerations in nuclear-waste treatment facilities. This is particularly relevant for facilities exploring innovative methods, such as accelerator-driven systems.

DOI： 10.1093/ptep/ptae139

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Physical Review Letters  

The neutron-rich unbound fluorine isotope F2130 has been observed for the first time by measuring its neutron decay at the SAMURAI spectrometer (RIBF, RIKEN) in the quasifree proton knockout reaction of Ne31 nuclei at 235 MeV/nucleon. The mass and thus one-neutron-separation energy of F30 has been determined to be Sn=-472±58(stat)±33(sys) keV from the measurement of its invariant-mass spectrum. The absence of a sharp drop in Sn(F30) shows that the "magic"N=20 shell gap is not restored close to O28, which is in agreement with our shell-model calculations that predict a near degeneracy between the neutron d and fp orbitals, with the 1p3/2 and 1p1/2 orbitals becoming more bound than the 0f7/2 one. This degeneracy and reordering of orbitals has two potential consequences: O28 behaves like a strongly superfluid nucleus with neutron pairs scattering across shells, and both F29,31 appear to be good two-neutron halo-nucleus candidates.

DOI： 10.1103/PhysRevLett.133.082501

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Publishing type：Research paper (scientific journal)   Publisher：Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms  

Silicon-insulated gate bipolar transistors (Si-IGBTs) are widely used for power control. In this study, we measured the energy deposited inside a commercial device with neutrons irradiation from 252Cf. We irradiated the device from the sealing and heat sink sides to evaluate the directional characteristics. A radiation simulation analysis was performed to understand the measurement results. The experiment and simulation showed that energy deposition in the device occurs through elastic scattering of neutrons and nuclear reactions. In particular, protons were generated by elastic scattering in the sealing material when the device was irradiated from the sealing side. Thus, the effect of neutrons on commercial Si-IGBTs is due to not only reactions inside the device but also secondary particles from the sealing material. When irradiated with high-energy neutrons, the knocked-out protons from sealing possibly cause single-event burnout (SEB). Therefore, the probability of SEB may depend on the direction of neutron incidence.

DOI： 10.1016/j.nimb.2024.165374

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： https://doi.org/10.1016/j.nima.2023.168984

Repository Public URL： https://hdl.handle.net/2324/7174411

Publishing type：Research paper (scientific journal)   Publisher：Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment  

In recent years, particle discrimination methods based on digital waveform analysis techniques for neutron-transmutation-doped silicon (nTD-Si) detectors have become widely used for the identification of low-energy charged particles. Although the particle discrimination capability of this method has been well demonstrated for small incident angles, the particle discrimination performance may be affected by changes in the detector response when the detector is moved closer to the charged particle source and the incident position distribution and incident angle distribution to the detector become wide. In this study, we performed a beam test for particle discrimination in light-charged (Z≤2) particles using the digital waveform analysis method with a pad-type nTD-Si detector and investigated the dependence of the performance of the particle discrimination on the incident position and incident angle. As the incident angle increased, a decrease in the maximum current was observed, which was sufficient to affect the performance of the particle discrimination. This decrease can be expressed as a function of the penetration depth of the charged particles into the detector, which varies for each nuclide.

DOI： 10.1016/j.nima.2023.168984

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Language：Others   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

γ emission probabilities from unbound states in 78,80Se, populated by a neutron-transfer reaction (d,p) on 77,79Se nuclei in inverse kinematics, were measured by directly detecting reaction residues. Assuming the spin distribution at the respective excitation energy of the unbound state, the cross-sections of the 79Se(n,γ)80Se reaction were evaluated using the γ emission probabilities. The surrogate-ratio method with the experimental γ emission probabilities of 78,80Se was also employed to deduce the cross-sections of 79Se(n,γ) reaction by incorporating the theoretical evaluations of the neutron-capture reaction on the isomeric state in 77Se. Our two cross-sections are in good agreement with existing nuclear data compilations for the neutron-capture reaction on 79Se. The presented method contributes to the body of existing knowledge by providing approaches for determining the neutron capture cross-sections of radioactive nuclei at various neutron energies.

DOI： 10.1016/j.physletb.2024.138470

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Language：Others   Publishing type：Research paper (scientific journal)   Publisher：Oxford University Press (OUP)  

Abstract

The deuteron is a loosely bound system which can easily break up into its constituent proton and neutron whilst in the presence of Coulomb and nuclear fields. Previous experimental studies have shown that this breakup process has a significant impact on residual nucleus production from deuteron bombardment in the high energy range of 50 – 210 MeV/nucleon. However, there remains a lack of cross-section data at energies below 50 MeV/nucleon. The current study determined 93Zr + d reaction cross sections under inverse kinematics at approximately 28 MeV/nucleon using the BigRIPS separator, OEDO beamline, and SHARAQ spectrometer. Cross sections from this research were compared with previous measurements and theoretical calculations. The experimental results show a large enhancement of the production cross sections of residual nuclei, especially those produced from a small number of particle emissions, compared to the proton-induced reaction data at similar bombarding energy. The DEURACS calculation, which quantitatively takes deuteron-breakup effects into account, reproduces the data well. As a long-lived fission product, 93Zr remains a challenge for nuclear waste disposal and treatment. This study’s low-energy data may assist future consideration of nuclear-waste treatment facilities, where 93Zr + d may feasibly transmute the waste into short-lived/stable nuclei.

DOI： 10.1093/ptep/ptad139

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Progress of Theoretical and Experimental Physics  

We have measured the differential cross section and analyzing power for (p, 2p) reactions that lead to discrete states of residual nuclei at an incident energy of 197 MeV for five kinds of target nuclei, 12C, 16O, 40,48Ca, and 90Zr. The data are compared with distorted-wave impulse approximation calculations using two kinds of global optical potentials. The spectroscopic factors obtained from these calculations agree with those determined in (e, e′p) studies within 20%, except for one orbital of the 90Zr nucleus where the distortion effect is much greater than that for the other orbitals of 90Zr and for other target nuclei. We also observed a clear and visibly distinct j-dependence in the analyzing power.

DOI： 10.1093/ptep/ptad116

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

We have launched a new research project named “ONOKORO” to elucidate the formation mechanism of clusters in atomic nuclei. The project comprehensively investigates clustering phenomena in the medium-to-heavy mass region with inverse-kinematics cluster-knockout reactions at the intermediate energy facilities. The new detector array named “TOGAXSI” is under construction for this purpose. It measures scattering angles and the energies of deuterons, tritons, 3He, and α particles emitted at forward angles from the cluster-knockout reactions. It also measures the recoil protons emitted from the scattering events at large angles. High-angular and high-energy resolutions with wide solid angles are required to achieve a good cluster separation energy resolution and a reasonably high yield. The designed telescope consists of silicon trackers and GAGG:Ce calorimeters. This paper shows the required conditions and design concepts of TOGAXSI.

DOI： 10.1016/j.nimb.2023.05.054

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms  

The cluster-knockout reaction project, ONOKORO, has been launched to elucidate the formation mechanism of clusters in atomic nuclei. For the inverse-kinetics cluster-knockout reaction experiments, a new detector array is under development to measure energies and angles of light ions emitted in the reactions. The silicon tracker tracks the particles with good angular and energy-loss resolutions. A performance test of the silicon strip detectors with a thickness of 100μm and a strip width of 100μm was performed using prototype silicon detectors. The mono-energetic proton and α-particle beams were irradiated on the silicon detectors. The energy-loss spectra in silicon detectors showed a good signal-to-noise ratio. The threshold level for signal detection is seven sigma of noise level. Their dynamic ranges were optimized wide enough to detect charge number Z= 1 and Z= 2 ions emitted in the cluster-knockout reactions.

DOI： 10.1016/j.nimb.2023.05.055

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

Subjecting a physical system to extreme conditions is one of the means often used to obtain a better understanding and deeper insight into its organization and structure. In the case of the atomic nucleus, one such approach is to investigate isotopes that have very different neutron-to-proton (N/Z) ratios than in stable nuclei. Light, neutron-rich isotopes exhibit the most asymmetric N/Z ratios and those lying beyond the limits of binding, which undergo spontaneous neutron emission and exist only as very short-lived resonances (about 10−21s), provide the most stringent tests of modern nuclear-structure theories. Here we report on the first observation of 28O and 27O through their decay into 24O and four and three neutrons, respectively. The 28O nucleus is of particular interest as, with the Z = 8 and N = 20 magic numbers1,2, it is expected in the standard shell-model picture of nuclear structure to be one of a relatively small number of so-called ‘doubly magic’ nuclei. Both 27O and 28O were found to exist as narrow, low-lying resonances and their decay energies are compared here to the results of sophisticated theoretical modelling, including a large-scale shell-model calculation and a newly developed statistical approach. In both cases, the underlying nuclear interactions were derived from effective field theories of quantum chromodynamics. Finally, it is shown that the cross-section for the production of 28O from a 29F beam is consistent with it not exhibiting a closed N = 20 shell structure.

DOI： 10.1038/s41586-023-06352-6

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Other Link： https://www.nature.com/articles/s41586-023-06352-6

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

Detailed γ-ray spectroscopy of the exotic neon isotope 28Ne has been performed for the first time using the one-neutron removal reaction from 29Ne on a liquid hydrogen target at 240 MeV/nucleon. Based on an analysis of parallel momentum distributions, a level scheme with spin-parity assignments has been constructed for 28Ne and the negative-parity states are identified for the first time. The measured partial cross sections and momentum distributions reveal a significant intruder p-wave strength providing evidence of the breakdown of the N=20 and N=28 shell gaps. Only a weak, possible f-wave strength was observed to bound final states. Large-scale shell-model calculations with different effective interactions do not reproduce the large p-wave and small f-wave strength observed experimentally, indicating an ongoing challenge for a complete theoretical description of the transition into the island of inversion along the Ne isotopic chain.

DOI： 10.1016/j.physletb.2023.138038

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Other Link： https://www.sciencedirect.com/science/article/pii/S0370269323003726

Language：English   Publishing type：Research paper (scientific journal)  

DOI： https://doi.org/10.1051/epjconf/202328401041

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Physical Review C  

The nucleus Ne29 is situated at the border of the island of inversion. Despite significant efforts, no bound low-lying intruder f7/2 state, which would place Ne29 firmly inside the island of inversion, has yet been observed. Here, the first investigation of unbound states of Ne29 is reported. The states were populated in Ne30(p,pn) and Na30(p,2p) reactions at a beam energy of around 230 MeV/nucleon, and analyzed in terms of their resonance properties, partial cross sections, and momentum distributions. The momentum distributions are compared to calculations using the eikonal, direct reaction model, allowing ℓ assignments for the observed states. The lowest-lying resonance at an excitation energy of 1.48(4) MeV shows clear signs of a significant ℓ=3 component, giving first evidence for f7/2 single particle strength in Ne29. The excitation energies and strengths of the observed states are compared to shell-model calculations using the sdpf-u-mix interaction.

DOI： 10.1103/PhysRevC.105.034301

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Language：Others   Publishing type：Research paper (scientific journal)  

A method for controlling the energy of slowed-down RI beams with the goal energy of 20 MeV/u was developed at the RIKEN RI Beam Factory. The 93Zr beam energy was successfully tuned to 20.2 MeV/u in a single step by adjusting its momentum selected by the first dipole magnet after a primary target. A method for particle identification was developed for the secondary reaction fragments at 50 MeV/u. The dispersive mode was applied to the ZeroDegree spectrometer to measure the momentum at the final focus F11. The reaction fragments were stopped in the multi-sampling ionization chamber (MUSIC) placed at F11, which measured the ΔE−E of the beam particles. In addition, the range R in MUSIC was determined with a resolution of 1.4 mm (σ) by using the energy ratio obtained from multi-sampled energy deposits. The atomic number was determined from the E−R correlation with a resolution of 0.15 (σ). To distinguish the charge state of the RI beam after the secondary reaction target, the range with the correction for the β dependence was combined with the mass-to-charge ratio determined from the time-of-flight and magnetic-rigidity measurements. A 5.6 σ separation was obtained between 92Zr40+ and 90Zr39+ using these two values.

DOI： 10.1016/j.nima.2020.164687

Language：Others   Publishing type：Research paper (scientific journal)  

DOI： 10.1103/physrevlett.125.122501

Language：Others   Publishing type：Research paper (scientific journal)  

© 2019 Elsevier B.V. The Optimized Energy Degrading Optics (OEDO) beamline was constructed at RIBF to produce slowed-down, well-focused radioactive-isotope beams at 10–50 MeV/u, and began operation in June 2017. We examined the performance of the OEDO system by decelerating high-energy medium-mass radioactive ions. The main components of the OEDO beamline are two superconducting quadrupole triplet magnets and one radio-frequency deflector. This paper introduces the unique design of the ion optics of the beamline and describes the achieved performance of the beamline in the commissioning and following physics experiments. We will discuss the properties of energy-degraded beams produced by the OEDO beamline by comparison of simulations and the achieved performance.

DOI： 10.1016/j.nimb.2019.06.006

Language：English   Publishing type：Research paper (scientific journal)  

DOI： https://doi.org/10.1038/s42005-019-0165-1

Language：English   Publishing type：Research paper (scientific journal)  

© 2019 The Author(s) 2019. Published by Oxford University Press on behalf of the Physical Society of Japan. The Optimized Energy Degrading Optics (OEDO) beamline is an upgrade of the High-resolution beamline at the RI Beam Factory at RIKEN. Its purpose is to measure nuclear reactions induced by radioactive ions at $10$-$50$ MeV/u. The main components of the OEDO beamline are two superconducting quadrupole triplet magnets and one radio-frequency deflector, which were recently installed. This setup produces slowed-down, well-focused radioactive-isotope beams by using a degree of freedom in the longitudinal phase space of the beam. This paper describes the OEDO beamline in detail, discusses the unique concept of its ion optics, and demonstrates its feasibility by conducting measurements with medium-mass radioactive-isotope beams.

DOI： 10.1093/ptep/ptz007

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1093/ptep/ptz028

Language：Others   Publishing type：Research paper (scientific journal)  

© 2018 A high position resolution neutron detector for time-of-flight measurements is being developed to measure the [Formula presented] 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 [Formula presented]. 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 [Formula presented]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.

DOI： 10.1016/j.nima.2018.10.153

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1093/ptep/pty138

Event date： 2024.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：理化学研究所（埼玉県和光市）   Country：Japan  

Event date： 2024.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：北海道大学札幌キャンパス（北海道札幌市）   Country：Japan  

Event date： 2024.9

Language：Japanese   Presentation type：Poster presentation  

Venue：株式会社ソシオネクスト 本社   Country：Japan  

Event date： 2024.7

Language：English   Presentation type：Poster presentation  

Venue：Vienna International Center   Country：Austria  

Event date： 2024.3

Language：Japanese   Presentation type：Symposium, workshop panel (public)  

Venue：近畿大学東大阪キャンパス（大阪府東大阪市）   Country：Japan  

Event date： 2024.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：近畿大学東大阪キャンパス（大阪府東大阪市）   Country：Japan  

Event date： 2023.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：理化学研究所 和光キャンパス（埼玉県和光市）   Country：Japan  

Event date： 2023.11

Language：Japanese   Presentation type：Symposium, workshop panel (public)  

Venue：東海村産業・情報プラザ「アイヴィル(iVil)」（茨城県東海村）   Country：Japan  

Other Link： https://conference-indico.kek.jp/event/238/contributions/4752/

Event date： 2023.11

Language：Japanese   Presentation type：Symposium, workshop panel (public)  

Venue：東海村産業・情報プラザ「アイヴィル(iVil)」（茨城県東海村）   Country：Japan  

Other Link： https://conference-indico.kek.jp/event/238/contributions/4749/

Event date： 2023.9

Language：Japanese   Presentation type：Symposium, workshop panel (public)  

Venue：東北大学青葉山キャンパス   Country：Japan  

Event date： 2022.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：茨城大学日立キャンパス   Country：Japan  

近年、半導体デバイスの微細化によりミューオン起因のソフトエラーが注目されている。負ミューオン原子核捕獲反応 (μNC) により発生する二次軽荷電粒子がソフトエラーの原因になることが指摘されている。そこで、我々はミューオン起因ソフトエラー発生率の評価に必要なμNCで生成する二次軽荷電粒子のエネルギースペクトルを実測するため、荷電粒子測定系の開発を行っている。本測定系では、荷電粒子のエネルギーごとに粒子識別方法の異なる２種類のテレスコープを用いる。低エネルギー粒子はnTD-Si検出器によって検出し、波形解析法により粒子識別を行う。また、高エネルギー粒子はSi検出器とCsIシンチレータにより検出し、ΔE-E法により粒子識別を行う。本講演では、九州大学タンデム加速器施設で行った測定系の動作テストについて報告する。

Event date： 2022.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：茨城大学日立キャンパス   Country：Japan  

九州大学加速器・ビーム応用科学センターのタンデム加速器施設においてnTD-Si検出器を用いた波形解析法による軽荷電粒子の弁別性能評価実験を行った。nTD-Si検出器に入射する軽荷電粒子の位置および入射角度を変えた測定を行い、それらが波形解析法による粒子弁別能に与える影響を評価した。本講演では、性能評価実験の詳細および解析結果について報告する。

Event date： 2022.7

Language：English   Presentation type：Oral presentation (general)  

Venue：Online   Country：Japan  

Other Link： https://indico.frib.msu.edu/event/52/

Event date： 2022.5 - 2022.6

Language：English   Presentation type：Oral presentation (general)  

Venue：理研仁科センター   Country：Japan  

Event date： 2022.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：大阪大学 吹田キャンパス   Country：Japan  

Event date： 2021.10 - 2022.10

Language：English   Presentation type：Oral presentation (general)  

Venue：オンライン   Country：Japan  

Event date： 2021.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン   Country：Japan  

Event date： 2019.8

Language：English   Presentation type：Oral presentation (general)  

Venue：Rikkyo University   Country：Japan  

Event date： 2019.5

Language：English   Presentation type：Oral presentation (general)  

Venue：Chine National Convention Center, Beijing   Country：China  

Event date： 2017.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：北海道大学   Country：Japan  

Event date： 2017.7

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：理研仁科センター   Country：Japan  

Event date： 2017.5

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東北大学   Country：Japan  

Event date： 2017.5

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：大阪市立大学   Country：Japan  

Event date： 2016.10 - 2016.11

Language：English   Presentation type：Oral presentation (general)  

Venue：Tokyo Institute of Technology   Country：Japan  

Other Link： http://www.crines.titech.ac.jp/ines5/

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Type：Peer review 

Number of peer-reviewed articles in foreign language journals：2

Number of peer-reviewed articles in Japanese journals：0

Proceedings of International Conference Number of peer-reviewed papers：0

Proceedings of domestic conference Number of peer-reviewed papers：0

Type：Competition, symposium, etc. 

Type：Peer review 

Number of peer-reviewed articles in foreign language journals：0

Number of peer-reviewed articles in Japanese journals：0

Proceedings of International Conference Number of peer-reviewed papers：0

Proceedings of domestic conference Number of peer-reviewed papers：9

Type：Competition, symposium, etc. 

Number of participants：80