RIBF Thesis Awards (RIBF Users Group Thesis Awards)
The RIBF Thesis Awards, formerly known as the RIBF Users Group Thesis Awards, were established in 2012 to recognize outstanding young scholars who have earned their doctoral degree based on research conducted at RIBFeither through experiments utilizing facilities such as BigRIPS, GARIS, CRIB, or RIPS, or through theoretical studies closely related to RIBF physics. Recipients are selected by the Thesis Award Selection Committee and are invited to deliver a special presentation at the annual RIBF Users Meeting.
2025
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We are pleased to announce that the RIBF Thesis Award 2025 will be presented to Dr. Akane Sakaue (RIKEN Nishina Center) in recognition of her outstanding contributions to physics research at RIBF. Dr. Sakaue obtained her Ph.D. from Kyoto University in March 2025, with the thesis entitled "Observation of double Gamow-Teller transition at high excitation energies by the (12C, 12Be(0+2)) reaction at 250 MeV/nucleon". Dr. Sakaue's thesis reports the first quantitative determination of double Gamow-Teller (DGT) strength distributions over a wide excitation-energy range, achieved through the (12C, 12Be(0+2)) reaction at the RIKEN Radioactive Isotope Beam Factory (RIBF). Using a 48Ca target, the study determined the DGT strength distribution to 48Ti. The experiment employed a unique and challenging setup: a 12C primary beam was directed onto the 48Ca target located at F0, and the produced 12Be(0+2) isomer was momentum-analyzed between F0 and F5 with high missing-mass resolution using dispersion matching. At the F8 focal plane, the isomer was stopped and selectively identified by detecting two 511 keV gamma rays from its e+e- decay, measured with the DALI2 array. Dr. Sakaue has led a large-scale collaboration throughout all stages of the research, pioneering critical advancements such as ion-optics tuning for dispersion matching, background-suppression techniques, and an innovative stopper system for isomer tagging. Her efforts yielded the first excitation-energy spectra of 48Ti via the 48Ca(12C, 12Be(0+2))48Ti reaction, revealing distinctive bumped structures at forward angles where DGT transitions are most prominent. She conducted the complex reaction calculations and multipole decomposition analyses necessary to extract the double Gamow-Teller strength distribution, identifying a candidate DGT giant resonance around 20 MeV. Her thesis also highlights future prospects for spin-isospin response studies and applications to double-beta decay, demonstrating both significant scientific impact and methodological innovation. The award ceremony will be at the next RIBF Users Meeting, which is tentatively planned to be held in March 2026. Thank you very much again for all applications, nominations, and support! With best regards, Kenjiro Miki (RIBF-UEC chair) Hiroyoshi Sakurai (Director of Nishina Center for Accelerator-Based Science) |
2024
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We are pleased to announce that the RIBF Users Group Thesis Awards for 2024 will be presented to Dr. Mădălina Enciu (Technische Universität Darmstadt) for her outstanding Ph.D. thesis, entitled "Extended p3/2 neutron orbital and the N=32 shell closure in 52Ca" (Technische Universität Darmstadt, 2023). We note two major accomplishments in her thesis project. Dr. Mădălina Enciu first conducted a comprehensive investigation of the neutron shell structure of neutron-rich calcium isotopes. She successfully analyzed the 52Ca(p,pn) reaction measured at SAMURAI, integrating data from a wide range of detectors. Her analysis confirmed that 52Ca is a neutron-closed-shell nucleus. Additionally, by developing a novel method for analyzing momentum distributions, in collaboration with nuclear theorists, she indicated that the valence p3/2 neutrons in 52Ca have a large spatial extension, 0.61(23) fm larger than the f7/2 neutrons. Her thesis also includes a systematic study of the nuclei 53Ca and 54Ca where the results for the size of p and f orbitals were in agreement with her initial findings for 52Ca. The innovative method she developed has attracted considerable interest for future research activities. In the second part of her work, she made crucial contributions to the development of the silicon tracker STRASSE and its associated liquid hydrogen target, which are essential for advanced in-beam gamma and missing-mass spectroscopy. She played a key role in validating the full operation of the prototype system, particularly the readout electronics. Additionally, she advanced the development of the liquid hydrogen target, including building the necessary tools and producing target cells capable of sustaining high pressures. The target system she developed will not only benefit STRASSE experiments, but will also be applied to a variety of RIBF experiments. With best regards, Kenjiro Miki (RIBF-UEC chair) Hiroyoshi Sakurai (Director of Nishina Center for Accelerator-Based Science) |
2023
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We are pleased to announce that the RIBF Users Group Thesis Awards for 2023 will be presented to Dr. Shun Iimura (Rikkyo Univ.) and Dr. Yoshiki Chazono (RIKEN) for their outstanding contributions to the physics at RIBF. Dr. Shun Iimura receives the award for his Ph.D. thesis, entitled "Development of RF carpet type He gas cell and high-precision mass measurement of neutron-rich nuclei at around A=50−60 with MRTOF" (Osaka University, 2022). In this work, Dr. Iimura spent countless hours on the development of the helium gas stopping cell installed at the end of the ZeroDegree beamline iteratively designing, assembling, and performing offline testing. The gas cell allows efficiently converting the relativistic beams delivered by BigRIPS to low-energy beams amenable to ion trapping experiments. With the completion of the gas cell, he devoted considerable time to the tuning of the multi-reflection time-of-flight (MRTOF) mass spectrograph achieving mass resolving powers approaching 1,000,000. With such high resolving power, the MRTOF could achieve a mass precision of 10 keV/c2 with just 25 detected ions. Combining this with its ability to simultaneously analyze multiple species of nuclides, he was able to perform highly efficacious atomic mass measurements in parallel with in-beam gamma-decay studies being performed by separate researchers. To analyze these mass measurement data, he developed a new method of drift correction using polynomial functions to better account for fitting errors in the reference peak. The results of the high-precision atomic mass measurements showed significant deviation from previous values derived from the magnetic-rigidity measurements, and indicated a lack of N=34 shell closure for Ti and V. The high performance of MRTOF will make a harvest of the mass measurements spanning the entire nuclear chart, leading not only to the detailed studies of exotic nuclear structure but also to the understanding of nucleosynthesis in the universe. Dr. Yoshiki Chazono receives the award for his Ph.D. thesis, entitled "New reaction model for revealing deuteron inside nuclei" (RCNP, Osaka University, 2022). In this work, Dr. Chazono proposed a new reaction model for describing the proton-induced deuteron knockout reaction (p,pd) to investigate the nature of deuteron and clustering inside nuclei. Recently, the proton-induced alpha knockout reaction (p,pα) has attracted increasing interest as an essential probe for detecting alpha clustering in atomic nuclei. Similarly, the (p,pd) reaction is expected to be an efficient probe for deuteron formation inside nuclei. However, in contrast to an alpha cluster, a deuteron is a weakly-bound system, whose breakup and couplings with continuum states cannot be neglected. In the thesis, Dr. Chazono attacked this problem, developing 1) a combination of the distorted-wave impulse approximation (DWIA) with a microscopic pn-pair wave function based on a pn hole-hole random phase approximation (RPA); 2) a reaction theory for p-d elastic scattering and a deuteron breakup d(p,p)pn reactions, which are elementary processes in the (p,pd) reaction; and 3) a new theoretical framework, named the continuum-discretized coupled-channel impulse approximation (CDCCIA), which takes into account the breakup effects of a weakly-bound deuteron. With the newly developed theory, Dr. Chazono demonstrated the importance of reformations (or "back couplings") of a broken deuteron that can hinder elastic (p,pd) cross sections. In particular, his work is behind the birth of the ONOKORO project, where the nature of light clusters, such as deuteron, triton, 3He, and alpha particles, is explored via knockout reactions. His model is the key to upcoming cluster knockout experiments at RIBF. With best regards, Yuichi Ichikawa (RIBF-UEC chair) Hiroyoshi Sakurai (Director of Nishina Center for Accelerator-Based Science) |
2022
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We are pleased to announce that the RIBF Users Group Thesis Awards for 2022 will be presented to Dr. Toshitaka Niwase (KEK) and Dr. Tomoya Naito (RIKEN) for their outstanding contributions to the physics at RIBF. Dr. Toshitaka Niwase receives the award for his PhD thesis, titled “First direct mass measurement of superheavy nuclide via MRTOF mass spectrograph equipped with an alpha-TOF detector” (Kyushu University, 2021). In this work, Dr. Niwase presents the development of an alpha-TOF detector to equip the MRTOF mass spectrograph in order to suppress background events by tagging the alpha decay of the nucleus of interest, which enables precise mass measurements of nuclei with an extremely low production rate, such as superheavy nuclei. Dr. Niwase played a major role in developing the detector and conducting the experiments. The detector has been applied to the mass measurement of 206,207Ra and 257Db - the latter one is the first direct mass measurement of a superheavy nucleus. The results are in agreement with existing data measured with indirect methods, providing an experimental demonstration of the capability of the new technique to perform a Z and A identification with a single event only. Further, the thesis includes numerical simulations for 263Sg and 267Hs, and discusses future mass measurements of various superheavy elements and a possible application to beta decays which will be useful to search for neutron-rich superheavy elements. The technique developed in the thesis has paramount importance in future superheavy element research. Dr. Tomoya Naito receives the award for his PhD thesis, titled “On isospin symmetry breaking in nuclear density functional theory” (The University of Tokyo, 2022). In this work, Dr. Naito discusses systematically the effects of the isospin symmetry breaking (ISB) on ground states of atomic nuclei by incorporating those effects from electromagnetic and nuclear interactions as much as possible to the nuclear energy density functional (EDF) approach. In the first part of the thesis, Dr. Naito adopted the so-called generalized gradient approximation for the Coulomb EDF to handle the electromagnetic interaction more accurately, which has been used in condensed matter physics, but not in nuclear physics community. Furthermore, Dr. Naito included the nucleon finite-size effect, the vacuum polarization effect, the effect from the electromagnetic spin-orbit interaction, and the finite-light-speed correction. It is found that the nucleon finite-size effect and the vacuum polarization effect are on the order of a few MeV in 208Pb and are crucial for accurately describing nuclear masses. In the latter part of the thesis, Dr. Naito discusses the ISB effects from the nuclear interaction on ground-state properties of doubly-magic nuclei, dividing the nuclear interaction into two parts: charge symmetry breaking (CSB) and charge independence breaking (CIB) terms. It is found that the CSB component is more sensitive to the mirror energy difference and neutron-skin thickness than the CIB component. In the thesis, Dr. Naito proposed a new way to determine the CSB strength in a nuclear EDF in combination with ab initio calculations, which is an important step towards constructing an ab-initio-based EDF. Dr. Naito's work offers methodologies for quantifying the ISB effects and is of substantial importance in future developments of more reliable EDFs. With best regards, Yuichi Ichikawa (RIBF-UEC chair) Hiroyoshi Sakurai (Director of Nishina Center for Accelerator-Based Science) |
Archive of RIBF Thesis Awards
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