arXiv subjects

Futoshi Minato

Publications and source records attributed to Futoshi Minato.

At least 19 recordsLinked to original sources

arXiv2026

Muon Nuclear Data Development Project

Negative muon-induced nuclear reactions play a critical role in a wide range of scientific and technological applications; however, comprehensive nuclear data for these processes remain unavailable. To address this gap, we have launched the Muon Nuclear Data (muND) Development Project in Japan, aiming to construct a dedicated data library for muon capture reactions. The library consists of four sub-libraries: muonic X-ray energies and intensities (XR), lifetimes of muonic atoms and nuclear capture rates (LT), energy spectra of emitted particles (ES), and production branching ratios of residual nuclei (BR). This project integrates experimental measurements, theoretical modeling, and machine learning techniques to compile and evaluate the data. We report the current status and recent progress of each sub-library.

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arXiv2026

Energy spectra of light charged particles emitted following muon nuclear capture on $^\mathrm{nat}$Si

Background: Charged-particle emission following muon nuclear capture (muNC) probes the de-excitation dynamics of highly excited nuclei, particularly the interplay between preequilibrium and evaporation processes. While proton emission has been relatively well studied, data on composite charged particles remain limited, especially for low-energy alpha particles. Purpose: This work aims to measure energy spectra for individual charged-particle species following muNC on silicon and constrain theoretical descriptions of preequilibrium, evaporation, and composite-particle emission. Method: An experiment was performed at the RIKEN-RAL Muon Facility. Charged particles were identified using Delta E-E telescopes and digital pulse-shape analysis with nTD-Si detectors. Initial energy spectra were reconstructed by unfolding and compared with the microscopic and evaporation model (MEM) and PHITS calculations incorporating the surface coalescence model and meson-exchange-current extension. Results: Energy spectra of protons, deuterons, tritons, and alpha particles were extracted over a broad energy range, including the first measurement of the low-energy alpha-particle spectrum. MEM more closely reproduces the proton, deuteron, and triton spectral shapes and describes the low-energy alpha-particle spectrum well. PHITS reproduces the overall slope of the alpha-particle spectrum but exhibits particle-dependent discrepancies in absolute yields, including an overestimation of the evaporation component for all four species. Conclusion: The results demonstrate particle-species-dependent differences in charged-particle emission following muNC. These spectra constrain descriptions of preequilibrium and evaporation processes and highlight the need for improved modeling of composite-particle emission.

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arXiv2025

Nuclear Responses to Two-Body External Fields Studied with the Second Random-Phase-Approximation

This study investigates nuclear responses to two body external fields, interpreted as double phonon excitations, within the subtracted second random phase approximation (SSRPA) for 16O and 40Ca. To clarify the underlying characteristics of these modes, Hartree Fock(HF) and SSRPA with the diagonal approximation are first examined. The resulting strength distributions are nearly identical, indicating that residual interactions in the 1p1h sector contribute only weakly. This behavior contrasts with that of one body excitations, where coupling between 1p1h and 2p2h configurations is essential for generating collectivity. In the full SSRPA calculation, which incorporates the residual interaction among 2p2h configurations, the strength distributions are substantially modified. The double IS 0+ and 2+ modes show pronounced redistribution, with peaks shifted to lower energies and additional strength emerging at higher energies, whereas the double IV 1- mode shifts predominantly to higher energies due to a largely repulsive interaction, resulting in a resonance around twice the peak energy of the single giant dipole resonance. Analysis of single transition amplitudes reveals that low lying resonances are formed coherently through constructive neutron-neutron, proton-proton, and neutron-proton configurations, while high-lying resonances are dominated by neutron-proton configurations, reflecting their higher state density. These results demonstrate that double-phonon excitations cannot be described by simple folding of one-body responses; a fully microscopic treatment of 2p2h mixing, as provided by SSRPA, is essential.

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arXiv2025

Phenomenological refinement of $p$-$d$ elastic scattering descriptions towards the 3NF study in nuclei via the ($p,pd$) reaction

The ($p,pd$) reaction is expected to be a powerful tool for probing three-nucleon forces (3NFs) in nuclear medium since it can be essentially regarded as the $p$-$d$ elastic scattering inside nuclei. One of the important points in the theoretical description of the ($p,pd$) reaction is to calculate the $p$-$d$ scattering in a nucleus quantitatively using effective interactions. This work aims to develop a phenomenological approach to improve the quantitativity of the $p$-$d$ scattering cross section in free space calculated with effective interactions. The $p$-$d$ elastic amplitude is decomposed into a 2N part, described using 2N effective interactions, and a residual part, which the 2N part cannot describe. The latter is approximated by a superposition of Legendre polynomials, with coefficients treated as adjustable parameters. These parameters are determined to reproduce experimental $p$-$d$ differential cross-section data at various incident energies. The obtained parameters exhibit smooth energy dependence, which is approximated by quadratic functions. The numerical results with the analytic energy dependence also reproduce the experimental data. The developed approach works well for improving the $p$-$d$ scattering cross section in a wide range of incident energies. This work can be regarded as the first step toward the description of ($p,pd$) reactions taking 3NF effect in nuclear medium into account.

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arXiv2025

Correlations of $Q_{\beta}$-values with symmetry energy and effective mass studied within Skyrme energy--density functionals

The $\beta$-decay half-lives of nuclei are sensitive to the values of $Q_{\beta}$. For accurate theoretical predictions, it is essential to develop an effective interaction or an energy density functional (EDF) that can systematically reproduce experimental $Q_{\beta}$ values. The challenge lies in identifying an appropriate EDF for an accurate $Q_{\beta}$ prediction. To address this, we focus on the bulk properties of nuclei that have correlations with $Q_{\beta}$. The primary objective of this study is to determine which nuclear bulk properties are sensitive to $Q_{\beta}$, providing information on the key nuclear characteristics that influence $\beta$-decay calculations. We employ the Skyrme energy-density functionals to find correlations between $Q_{\beta}$ and the nuclear bulk properties, assuming spherical symmetry. Using $42$ different Skyrme EDFs, we analyze these correlations by evaluating Pearson linear coefficients, focusing particularly on the relationship between $Q_{\beta}$ and various nuclear properties. We found that the symmetry energy at low densities shows a correlation with the $Q_{\beta}$ value. In particular, this correlation becomes stronger for functionals with an effective mass close to $1$. However, as the nuclear density increases, the correlation weakens. From our analysis, we found that a symmetry energy of $32.8\pm0.7$~MeV and effective mass of $m^{*}/m\ge0.75$ at the saturation density is the most likely to systematically reproduce the experimental data of $Q_{\beta}$ systematically.

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arXiv2024

Transitions To Door-way States And Nuclear Responses Against 2-body External Fields

Nuclear microscopic structural models that treat two-body effective interactions self-consistently becomes available, one of which is second-random-phase-approximation (SRPA). SRPA can be used to study evolutions from 1 particle-1 hole (1p1h) to 2 particle-2 hole (2p2h) states from different point of view from reaction models. We studied nuclear excitations created by 1-body and 2-body external fields and discuss transitions between 1p1h and 2p2h states obtained by the SRPA approach.

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arXiv2024

Fission Fragment Yields Of $^{235}$U$(n_{th},f)$ Evaluated By The CCONE Code System

Fission fragment yield evaluations are one of the important nuclear data studies. Fission accompanies various physical observables such as prompt fission neutron, prompt fission gamma, and delayed-neutrons. When evaluating fission fragment yields, a study including correlations among those observables is essentially required. However, fission fragment yield data in the past JENDL libraries have been made by focusing only on experimental fragment yields, decay heats, and delayed neutron yields, and they have not been expanded into a wider range of fission observables. This is because the evaluation method adopted in the JENDL libraries could not study fission fragment yields and particle emissions from fragments simultaneously. To solve this problem, a calculation system with CCONE code is newly developed to estimate not only independent and cumulative fission fragment yields but also prompt fission neutron, prompt fission gamma, decay heats, and delayed-neutrons simultaneously. This system enables us to study a correlation between various fission observables. To determine lots of parameters in this system efficiently, a Gaussian process and a least square fitting are adopted. We tested the calculation system through a thermal neutron-induced fission on $^{235}$U. In this paper, we demonstrate the performance of the parameter search method and show that experimental fission fragment yield data and other observables resulting from fission are reproduced well by the new calculation system.

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arXiv2024

Muon Nuclear Data

We plan to develop a new nuclear database for muon-induced nuclear reactions (muon nuclear data). The database will consist of (1) energies and intensities of the muonic X rays, (2) lifetimes of the muonic atom, (3) production branching ratio of the residual nuclei by muon capture, (4) emission probabilities of the particles after muon capture, and (5) energy spectra of the emitted particles after muon capture. In this paper, we review the present status and current investigations for the muon nuclear data.

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arXiv2024

Calculation of Fission Fragment Yields for thermal neutron reaction of $^{239}$Pu

Fission fragment yield evaluation in the past has been done mainly by considering independent and cumulative fission yields. In addition to them, the fission fragment yields are related to various observables such as total kinetic energy, prompt fission neutron, decay heats, etc. Various improvements were carried out in the fission fragment yield evaluation of JENDL-5, however it did not consider correlations between such fission observables and fragment yields. A new evaluation including fission observables is thus required for next generation of evaluated data. We recently developed a new calculation system using CCONE code to calculate fission fragment yields. This calculation system enables us to compare various fission observables with the experimental data simultaneously. In this work, we calculated thermal-induced fission of 239Pu. We present the result of prompt fission neutrons, decay heats, and delayed neutrons

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arXiv2023

Postfission properties of uranium isotopes: A hybrid method with Langevin dynamics and the Hauser-Feshbach statistical model

Background: Precise understanding of nuclear fission is crucial for experimental and theoretical nuclear physics, astrophysics, and industrial applications; however, the complete physical mechanics is unresolved due to the complexities. Purpose: In this study, we present a new method to describe the dynamical-fission process and following prompt-neutron emission, where we combine the dynamical fission calculation based on the Langevin method and the Hauser-Feshbach statistical model. Methods: Two methods are connected smoothly within the universal charge distribution and the energy conservation, allowing us to calculate a sequence of fission dynamics and post-fission phase, including prompt neutron emission. Results: Using a certain set of model parameters, we successfully reproduce the experimental primary-fission yields, total kinetic energy, independent-fission yields, and prompt neutron emissions for the neutron induced fission of ${}^{236}$U, a compound nucleus of ${\rm n} + {}^{235}{\rm U}$. We elucidate the physical mechanism of the characteristic features observed in previous experiments, such as shell properties. Additionally, we apply our calculation to two very neutron-rich uranium isotopes, i.e., ${}^{250}$U and ${}^{255}$U, which are not experimentally confirmed but are important for r-process nucleosynthesis. Theoretical results indicate that ${}^{250}$U exhibits an asymmetric multiple-peak fission yield distribution, while the neutron-rich ${}^{255}$U has a single peak due to symmetric fission. Our method predicts post-neutron emission fragments, where ${}^{250}$U shows a stronger neutron emissivity than ${}^{255}$U. Conclusions: Our framework is highly reproducible in the experiments and shows that the number of emitted neutrons after fission differs significantly in neutron-rich uranium fission depending on distributions of fission variables.

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arXiv2023

$\beta$-decay half-lives as an indicator of shape-phase transition in neutron-rich Zr isotopes with particle-vibration coupling effect

[Background] $\beta$-decay half-life is sensitive to the shell structure near the Fermi levels. Nuclear deformation thus impacts the $\beta$-decay properties. [Purpose] A first-order shape-phase transition in neutron-rich Zr isotopes is predicted by some models. We investigate the $\beta$-decay half-lives of neutron-rich nuclei around $^{110}$Zr, where the shape-phase transition is predicted to occur, to see if the $\beta$-decay half-life can be an indicator of the shape changes. [Method] The proton-neutron quasiparticle random-phase approximation (RPA) is adopted to calculate the Gamow-Teller transitions. In addition, we apply the quasiparticle phonon-vibrational coupling (PVC) to consider the phonon couplings. [Results] The spherical and oblate configurations give similar half-lives but shorter ones than the prolate configuration at the RPA level. The PVC effect further reduces the half-lives in general, but the effect is smaller for the deformed configuration than that for the spherical one. As a result, it makes the shape change from the oblate configuration to the spherical configuration visible. Therefore, a sudden shortening of $\beta$-decay half-lives is always found at the nuclear shape changes. [Conclusions] $\beta$-decay half-life is an indicator of the shape-phase transition. The shape mixing and the roles of the triaxial deformation are subject to study in the future.

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arXiv2022

Nuclear Many-Body Effect on Particle Emissions Following Muon Capture on $^{28}$Si and $^{40}$Ca

Muon captures on nuclei have provided us with plenty of knowledge of nuclear properties. Recently, this reaction attracts attention in electronics, because it is argued that charged particle emissions following muon capture on silicon trigger non-negligible soft errors in memory devices. To investigate the particle emissions from a nuclear physics point of view, we develop a new approach using a microscopic model of muon capture and up-to-date particle emission models. We paid attention to the muon capture rates, the particle emission spectra, and the multiplicities that have a close interrelation with each other, and found that the nuclear many-body correlation including two-particle two-hole excitations is a key to explaining them simultaneously.

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arXiv2022

Calculation of $\beta$-decay half-lives with Skyrme Hartree-Fock-Bogoliubov+$pn$-QRPA and isoscalar pairing strengths optimized by a Bayesian method

For radioactive nuclear data, $\beta$ decay is one of the most important information and is applied to various fields. However, some of the $\beta$-decay data are not available due to experimental difficulties. From this respect, theoretically calculated results have been embedded in the $\beta$-decay data to compensate the missing information. To calculate the $\beta$-decay half-lives, a proton-neutron quasi-particle random phase approximation on top of a Skryme energy density functional is applied with an assumption of spherical symmetry. The isoscalar pairing strength is estimated by a Bayesian neutral network (BNN). We verify the predicted isoscalar pairing strengths by preparing the training data and test data. It was confirmed that the finite-range isovector pairing ensures the $\beta$-decay half-lives insensitive to the model space, while the zero-range one was largely dependent on it. The half-lives calculated with the BNN isoscalar pairing strengths reproduced most of experimental data, although those of highly deformed nuclei were underestimated. We also studied that the predictive performance on new experimental data that were not used for the BNN training and found that they were reproduced well. Our study demonstrates that the isoscalar pairing strengths determined by the BNN can reproduce experimental data in the same accuracy as other theoretical works.

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arXiv2021

$β$-Delayed Neutron and Fission Calculations with Relativistic QRPA and Statistical Model

A role of β-delayed neutron emission and fission in r-process nucleosynthesis attracts a high interest. Although the number of study on them covering r-process nuclei is increasing recently, uncertainties of β-delayed neutron and fission are still large for r-process simulations. Our purpose is to make a new database on β-delayed neutron emission and fission rates. To this end, the data that are not investigated experimentally have to be predicted. Microscopic theoretical approaches based on a nuclear energy density functional and statistical models are one of the competent tools for the prediction. To obtain βstrength function, p-n relativistic QRPA is adopted. Particle evaporations and fission from nuclear highly excited states are estimated by the Hauser-Feshbach statistical model. β-delayed neutron branching ratios (P_n) are calculated and compared with experimental data. β-delayed fission branching ratio (P_f) are also assessed by using four different fission barrier data. Calculated P_n values are in a good agreement with experimental data. It is found that energy withdrawal by β-delayed neutron emission sensitively varies P_n values for nuclei near the neutron drip line. P_f are sensitively dependent on fission barrier data. Newly calculated data on β-delayed neutron emission and fission are summarized as a table in supplement material. They are provided for studies of r-process as well as other fields such as nuclear engineering.

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arXiv2019

Theoretical study of $ \rm{Nb} $ isotope productions by muon capture reaction on $ {}^{100} \rm{Mo} $

The isotope $ {}^{99} \rm{Mo} $, the generator of $ {}^{99m} \rm{Tc} $ used for diagnostic imaging, is supplied by extracting from fission fragments of highly enriched uranium in reactors. However, a reactor-free production method of $ {}^{99} \rm{Mo} $ is searched over the world from the point of view of nuclear proliferation. Recently, $ {}^{99} \rm{Mo} $ production through a muon capture reaction was proposed and it was found that about $ 50 \, \% $ of $ {}^{100} \rm{Mo} $ turned into $ {}^{99} \rm{Mo} $ through $ {}^{100} \rm{Mo} \left( μ^-, n \right) $ reaction [arXiv:1908.08166]. However, the detailed physical process of the muon capture reaction is not completely understood. We, therefore, study the muon capture reaction of $ ^{100} \rm{Mo} $ by a theoretical approach. We used the proton-neutron QRPA to calculate the muon capture rate. The muon wave function is calculated with considering the electronic distribution of the atom and the nuclear charge distribution. The particle evaporation process from the daughter nucleus is calculated by a statistical model. From the model calculation, about $ 38 \, \% $ of $ {}^{100} \rm{Mo} $ is converted to $ {}^{99} \rm{Mo} $ through the muon capture reaction, which is in a reasonable agreement with the experimental data. It is revealed that negative parity states, especially $ 1^- $ state, play an important role in $ {}^{100} \rm{Mo} \left( μ^-, n \right) {}^{99} \rm{Nb} $. The feasibility of $ {}^{99} \rm{Mo} $ production by the muon capture reaction is also discussed. Isotope production by the muon capture reaction strongly depends on the nuclear structure.

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arXiv2018

Phenomenological level density model with hybrid parameterization of deformed and spherical state densities

A phenomenological level density model that has different level density parameter sets for the state densities of the deformed and the spherical states, and the optimization of the parameters using experimental data of the average s-wave neutron resonance spacing are presented. The transition to the spherical state from the deformed one is described using the parameters derived from a microscopic nuclear structure calculation. The nuclear reaction calculation has been performed by the statistical model using the present level density. Resulting cross sections for various reactions with the spherical, deformed and transitional target nuclei show a fair agreement with the experimental data, which indicates the effectiveness of the present model. The role of the rotational collective enhancement in the calculations of those cross sections is also discussed.

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arXiv2018

Neutron Energy Dependence of Delayed Neutron Yields and its Assessments

Incident neutron energy dependence of delayed neutron yields of uranium and plutonium isotopes is investigated. A summation calculation of decay and fission yield data is employed, and the energy dependence of the latter part is considered in a phenomenological way. Our calculation systematically reproduces the energy dependence of delayed neutron yields by introducing an energy dependence of the most probable charge and the odd-even effect. The calculated fission yields are assessed by comparison with JENDL/FPY-2011, delayed neutron activities, and decay heats. Although the fission yields in this work are optimized to delayed neutron yields, the calculated decay heats are in good agreement with the experimental data. Comparison of the fission yields calculated in this work and JENDL/FPY-2011 gave an important insight for the evaluation of the next JENDL nuclear data.

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arXiv2018

Spin-Isospin Properties of $N=Z$ Odd-Odd Nuclei from a Core+$pn$ Three-Body Model including Core Excitations

For $N=Z$ odd-odd nuclei, a three-body model assuming two valence particles and an inert core can provide an understanding of pairing correlations in the ground state and spin-isospin excitations. However, since residual core-nucleon interactions can have a significant impact on these quantities, the inclusion of core excitations in the model is essential for useful calculation to be performed. The effect of core excitations must be included in order to gain a detailed understanding of both the ground state and spin-isospin properties of these systems. To this end, we include the vibrational excitation of the core nucleus in our model. We solve the three-body core-nucleon-nucleon problem including core vibrational states to obtain the nuclear ground state as well as spin-isospin excitations. The spin-isospin excitations are examined from the point of view of SU(4) multiplets. By including the effect of core excitation, several experimental quantities of $N=Z$ odd-odd nuclei are better described, and the root mean square distances between proton and neutron and that between the center of mass of proton and neutron and core nucleus increase. Large $B$($M1$) and $B$(GT) observed for $^{18}$F and $^{40}$Ca were explained in terms of the SU(4) symmetry. The core nucleus is meaningfully broken by the residual core-nucleon interactions, and various quantities concerning spin-isospin excitations as well as the ground state become consistent with experimental data. Including the core excitation in the three-body model is thus important for a more detailed understanding of nuclear structure.

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