arXiv subjects

Katsuhisa Nishio

Publications and source records attributed to Katsuhisa Nishio.

4 recordsLinked to original sources

arXiv2025

Design of a Storage Ring based on a Fixed Field Alternating Gradient Configuration with an Internal Target for Heavy-Ion Beams with Stochastic Charge State Conversions

In the general use of a heavy-ion accelerator, an accelerated beam impinged on a target is spoiled into a beam dump. To make more efficient use of the beam, recycling of the beam passed through the target is proposed in the framework of the so-called energy recovery internal target (ERIT). In the ERIT system, the target is irradiated inside the circulating beam by recovering the energy lost in the target using rf cavities. So far, such a system has been realized only for proton beams. Here, the ERIT system for heavy-ion beam is demonstrated for the first time. A challenging issue is the circulation of all ions with different atomic charge. An ion has a probability of equilibrated charge state distribution after passing through the target, independent of the initial charge state. This phenomenon of stochastic charge state conversion (SCSC) causes rapid beam-emittance growth. To solve this problem, we developed a method to match the closed orbits and betatron functions of the beams in different charge states at the target location in a ring based on a scaling fixed field alternating gradient (FFA) lattice structure. We present the design of such an FFA ring and show, through full 6D beam tracking simulations, that transverse emittance growth can be effectively suppressed even in the presence of SCSC.

physics.acc-ph↗

arXiv2022

Design report of the KISS-II facility for exploring the origin of uranium

One of the critical longstanding issues in nuclear physics is the origin of the heavy elements such as platinum and uranium. The r-process hypothesis is generally supported as the process through which heavy elements are formed via explosive rapid neutron capture. Many of the nuclei involved in heavy-element synthesis are unidentified, short-lived, neutron-rich nuclei, and experimental data on their masses, half-lives, excited states, decay modes, and reaction rates with neutron etc., are incredibly scarce. The ultimate goal is to understand the origin of uranium. The nuclei along the pathway to uranium in the r-process are in "Terra Incognita". In principle, as many of these nuclides have more neutrons than 238U, this region is inaccessible via the in-flight fragmentation reactions and in-flight fission reactions used at the present major facilities worldwide. Therefore, the multi-nucleon transfer (MNT) reaction, which has been studied at the KEK Isotope Separation System (KISS), is attracting attention. However, in contrast to in-flight fission and fragmentation, the nuclei produced by the MNT reaction have characteristic kinematics with broad angular distribution and relatively low energies which makes them non-amenable to in-flight separation techniques. KISS-II would be the first facility to effectively connect production, separation, and analysis of nuclides along the r-process path leading to uranium. This will be accomplished by the use of a large solenoid to collect MNT products while rejecting the intense primary beam, a large helium gas catcher to thermalize the MNT products, and an MRTOF mass spectrograph to perform mass analysis and isobaric purification of subsequent spectroscopic studies. The facility will finally allow us to explore the neutron-rich nuclides in this Terra Incognita.

physics.ins-det↗

arXiv2017

A 4-dimensional Langevin approach to low-energy nuclear fission of $^{236}$U

We developed a four-dimensional Langevin model which can treat the deformation of each fragment independently and applied it to low energy fission of 236U, the compound system of the reaction n+$^{235}$U. The potential energy is calculated with the deformed two-centerWoods-Saxon (TCWS) and the Nilsson type potential with the microscopic energy corrections following the Strutinsky method and BCS pairing. The transport coefficients are calculated by macroscopic prescriptions. It turned out that the deformation for the light and heavy fragments behaves differently, showing a sawtooth structure similar to that of the neutron multiplicities of the individual fragments $ν$(A). Furthermore, the measured total kinetic energy TKE(A) and its standard deviation are reproduced fairly well by the 4D Langevin model based on the TCWS potential in addition to the fission fragment mass distributions. The developed model allows a multi-parametric correlation analysis among, e.g., the three key fission observables, mass, TKE, and neutron multiplicity, which should be essential to elucidate several long-standing open problems in fission such as the sharing of the excitation energy between the fragments.

nucl-th↗

arXiv2014

Towards a novel laser-driven method of exotic nuclei extraction-acceleration for fundamental physics and technology

The measurement of properties of exotic nuclei, essential for fundamental nuclear physics, now confronts a formidable challenge for contemporary radiofrequency accelerator technology. A promising option can be found in the combination of state-of-the-art high-intensity short pulse laser system and nuclear measurement techniques. We propose a novel Laser-driven Exotic Nuclei extraction-acceleration method (LENex): a femtosecond petawatt laser, irradiating a target bombarded by an external ion beam, extracts from the target and accelerates to few GeV highly-charged nuclear reaction products. Here a proof-of-principle experiment of LENex is presented: a few hundred-terawatt laser focused onto an aluminum foil, with a small amount of iron simulating nuclear reaction products, extracts almost fully stripped iron nuclei and accelerate them up to 0.9 GeV. Our experiments and numerical simulations show that short-lived, heavy exotic nuclei, with a much larger charge-to-mass ratio than in conventional technology, can be obtained in the form of an energetic, low-emittance, high-current beam.

physics.acc-ph↗