arXiv subjects

H. Fujita

Publications and source records attributed to H. Fujita.

At least 19 recordsLinked to original sources

arXiv2024

Understanding the total width of the $3_{1}^{-}$ state in $\mathrm{^{12}C}$

Recent measurements indicate that the previously established upper limit for the $γ$-decay branch of the $3_{1}^{-}$ resonance in $^{12}\textrm{C}$ at $E_{x} = 9.641(5)$ MeV may be incorrect. As a result, the $3_{1}^{-}$ resonance has been suggested as a significant resonance for mediating the triple-$α$ reaction at high temperatures above 2 GK. Accurate estimations of the $3_{1}^{-}$ contribution to the triple-$α$ reaction rate require accurate knowledge of not only the radiative width, but also the total width. In anticipation of future measurements to more accurately determine the $γ$-decay branch of the $3_{1}^{-}$ resonance, the objective of this work is to accurately determine the total width of the $3_{1}^{-}$ resonance. An evaluation was performed on all previous results considered in the current ENSDF average of 46(3) keV for the physical total width (FWHM) of the $3_{1}^{-}$ resonance in $^{12}\textrm{C}$. Significant unaccounted-for uncertainties and a misstated result were discovered in these previous results, leading to an invalid ENSDF average. In this work, the new global \textbf{R}-matrix analysis performed on direct-reaction data yields a formal total width of $Γ(E_{r}) = 46(2)$ keV and an observed total width of $Γ_{\textrm{obs}}(E_{r}) = 38(2)$ keV for the $3_{1}^{-}$ resonance. An observed total width of $Γ_{\textrm{obs}}(E_{r}) = 38(2)$ keV is recommended for the $3_{1}^{-}$ resonance in $\mathrm{^{12}C}$. This observed total width should be employed for future evaluations of the observed total radiative width for the $3_{1}^{-}$ resonance and its contribution to the high-temperature triple-$α$ reaction rate.

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arXiv2023

Optimization of Convolutional Neural Network Using the Linearly Decreasing Weight Particle Swarm Optimization

Convolutional neural network (CNN) is one of the most frequently used deep learning techniques. Various forms of models have been proposed and im-proved for learning at CNN. When learning with CNN, it is necessary to determine the optimal hyperparameters. However, the number of hyperparameters is so large that it is difficult to do it manually, so much research has been done on automation. A method that uses metaheuristic algorithms is attracting attention in research on hyperparameter optimization. Metaheuristic algorithms are naturally inspired and include evolution strategies, genetic algorithms, antcolony optimization and particle swarm optimization. In particular, particle swarm optimization converges faster than genetic algorithms, and various models have been proposed. In this paper, we pro-pose CNN hyperparameter optimization with linearly decreasing weight particle swarm optimization (LDWPSO). In the experiment, the MNIST data set and CIFAR-10 data set, which are often used as benchmark data sets, are used. By opti-mizing CNN hyperparameters with LDWPSO, learning the MNIST and CIFAR-10 datasets, we compare the accuracy with a standard CNN based on LeNet-5. As a result, when using the MNIST dataset, the baseline CNN is 94.02% at the 5th epoch, compared to 98.95% for LDWPSO CNN, which improves accuracy. When using the CIFAR-10 dataset, the Baseline CNN is 28.07% at the 10th epoch, compared to 69.37% for the LDWPSO CNN, which greatly improves accuracy. This paper is presented at the 36th Annual Conference of the Japanese Society for Artificial In-telligence. The final version is available at the following URL: https://doi.org/10.11517/pjsai.JSAI2022.0_2S4IS2b03

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arXiv2022

Damping of the isovector giant dipole resonance in $^{40,48}$Ca

The fine structure of the IsoVector Giant Dipole Resonance (IVGDR) in the doubly-magic nuclei $^{40,48}$Ca observed in inelastic proton scattering experiments under $0^\circ$ is used to investigate the role of different mechanisms contributing to the IVGDR decay width. Characteristic energy scales are extracted from the fine structure by means of wavelet analysis. The experimental scales are compared to different theoretical approaches allowing for the inclusion of complex configurations beyond the mean-field level. Calculations are performed in the framework of RPA and beyond-RPA in a relativistic approach based on an effective meson-exchange interaction, with the UCOM effective interaction and, for the first time, with realistic two- plus three-nucleon interactions from chiral effective field theory employing the in-medium similarity renormalization group. All models highlight the role of Landau fragmentation for the damping of the IVGDR, while the differences in the coupling strength between one particle-one hole (1p-1h) and two particle-two hole (2p-2h) correlated (relativistic) and non-correlated (non-relativistic) configurations lead to very different pictures of the importance of the spreading width resulting in wavelet scales being a sensitive measure of their interplay. The relativistic approach with particle-vibration coupling, in particular, shows impressive agreement with the number and absolute values of the scales extracted from the experimental data.

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arXiv2021

Fine Structure of the Isovector Giant Dipole Resonance in $^{142-150}$Nd and $^{152}$Sm

Background: Inelastic proton scattering at energies of a few hundred MeV and very-forward angles including $0^\circ$ has been established as a tool to study electric-dipole strength distributions in nuclei. The present work reports a systematic investigation of the chain of stable even-mass Nd isotopes representing a transition from spherical to quadrupole-deformed nuclei. Purpose: Extraction of the equivalent photo-absorption cross sections and analysis of their fine structure in the energy region of the IsoVector Giant Dipole Resonance (IVGDR). Method: Proton inelastic scattering reactions of 200 MeV protons were measured at iThemba LABS in Cape Town, South Africa. The scattering products were momentum-analysed by the K600 magnetic spectrometer positioned at $θ_{\mathrm{Lab}}=0^\circ$. Using dispersion-matching techniques, energy resolutions of $ΔE \approx 40 - 50$ keV were obtained. After subtraction of background and contributions from other multipoles, the spectra were converted to photo-absorption cross sections using the equivalent virtual-photon method. Results: Wavelet-analysis techniques are used to extract characteristic energy scales of the fine structure of the IVGDR from the experimental data. Comparisons with the Quasiparticle-Phonon Model (QPM) and Skyrme Separable Random Phase Approximation (SSRPA) predictions provide insight into the role of different giant resonance damping mechanisms. Conclusions: Fine structure is observed even for the most deformed nuclei studied. Fragmentation of the one particle-one hole ($1p1h$) strength seems to be the main source of fine structure in both spherical and deformed nuclei. Some impact of the spreading due to coupling of the two particle-two hole ($2p2h$) states to the $1p1h$ doorway states is seen in the spherical/transitional nuclei, where calculations beyond the $1p1h$ level are available.

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arXiv2020

Evolution of the dipole polarizability in the stable tin isotope chain

The dipole polarizability of stable even-mass tin isotopes 112,114,116,118,120,124 was extracted from inelastic proton scattering experiments at 295 MeV under very forward angles performed at RCNP. Predictions from energy density functionals cannot account for the present data and the polarizability of 208Pb simultaneously. The evolution of the polarizabilities in neighboring isotopes indicates a kink at 120Sn while all model results show a nearly linear increase with mass number after inclusion of pairing corrections.

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arXiv2020

Fine structure of the isoscalar giant monopole resonance in $^{48}$Ca

Experiments investigating the fine structure of the IsoScalar Giant Monopole Resonance (ISGMR) of 48Ca were carried out with a 200 MeV alpha inelastic-scattering reaction, using the high energy-resolution capability and the zero-degree setup at the K600 magnetic spectrometer of iThemba LABS, Cape Town, South Africa. Considerable fine structure is observed in the energy region of the ISGMR. Characteristic energy scales are extracted from the experimental data by means of a wavelet analysis and compared with the state-of-the-art theoretical calculations within a Skyrme-RPA (random phase approximation) approach using the finite-rank separable approximation with the inclusion of phonon-phonon coupling (PPC). Good agreement was observed between the experimental data and the theoretical predictions.

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arXiv2020

Electric and magnetic dipole strength in 112,114,116,118,120,124Sn

Inelastic proton scattering experiments were performed at the Research Center for Nuclear Physics, Osaka, with a 295 MeV beam covering laboratory angles 0°-6° and excitation energies 6-22 MeV. Cross sections due to E1 and M1 excitations were extracted with a multipole decomposition analysis and then converted to reduced transition probabilities with the "virtual photon method" for E1 and the "unit cross section method" for M1 excitations, respectively. Including a theory-aided correction for the high excitation energy region not covered experimentally, the electric dipole polarizability was determined from the E1 strength distributions. Total photoabsorption cross sections derived from the E1 and M1 strength distributions show significant differences compared to those from previous ($γ$,xn) experiments in the energy region of the isocvector giant dipole resonance (IVGDR). The widths of the IVGDR deduced from the present data with a Lorentz parameterization show an approximately constant value of about 4.5 MeV in contrast to the large variations between isotopes observed in previous work. The IVGDR centroid energies are in good correspondence to expectations from systematics of their mass dependence. Furthermore, a study of the dependence of the IVGDR energies on bulk matter properties is presented. The E1 strengths below neutron threshold show fair agreement with results from ($γ$,$γ$') experiments on 112,116,120,124Sn in the energy region between 6 and 7 MeV. At higher excitation energies large differences are observed pointing to a different nature of the excited states with small ground state branching ratios. The isovector spin-M1 strengths exhibit a broad distribution between 6 and 12 MeV in all studied nuclei.

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arXiv2020

Reexamination of $^{6}$Li scattering as a Probe to Investigate the Isoscalar Giant Resonances in Nuclei

Inelastic ${}^{6}$Li scattering at 100 MeV/u on ${}^{12}$C and ${}^{93}$Nb have been measured with the high-resolution magnetic spectrometer Grand Raiden. The magnetic-rigidity settings of the spectrometer covered excitation energies from 10 to 40 MeV and scattering angles in the range $0^\circ < θ_{\text{lab.}}< 2^\circ$. The isoscalar giant monopole resonance was selectively excited in the present data. Measurements free of instrumental background and the very favorable resonance-to-continuum ratio of ${}^{6}$Li scattering allowed for precise determination of the $E0$ strengths in ${}^{12}$C and ${}^{93}$Nb. It was found that the monopole strength in ${}^{12}$C exhausts $52 \pm 3^\text{(stat.)} \pm 8 ^\text{(sys.)}$\% of the energy-weighted sum rule (EWSR), which is considerably higher than results from previous $α$-scattering experiments. The monopole strength in ${}^{93}$Nb exhausts $92 \pm 4^\text{(stat.)} \pm 10 ^\text{(sys.)}$\% of the EWSR, and it is consistent with measurements of nuclei with mass number of $A\approx90$. Such comparison indicates that the isoscalar giant monopole resonance distributions in these nuclei are very similar, and no influence due to nuclear structure was observed.

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arXiv2017

Deformation dependence of the isovector giant dipole resonance: The neodymium isotopic chain revisited

Proton inelastic scattering experiments at energy E_p = 200 MeV and a spectrometer scattering angle of 0 degree were performed on 144,146,148,150Nd and 152Sm exciting the IsoVector Giant Dipole Resonance (IVGDR). Comparison with results from photo-absorption experiments reveals a shift of resonance maxima towards higher energies for vibrational and transitional nuclei. The extracted photo-absorption cross sections in the most deformed nuclei, 150Nd and 152Sm, exhibit a pronounced asymmetry rather than a distinct double-hump structure expected as a signature of K-splitting. This behaviour can be related to the proximity of these nuclei to the critical point of the phase shape transition from vibrators to rotors with a soft quadrupole deformation potential. Self-consistent random-phase approximation (RPA) calculations using the SLy6 Skyrme force provide a relevant description of the IVGDR shapes deduced from the present data

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arXiv2017

Test of the Brink-Axel hypothesis for the pygmy dipole resonance

The gamma strength function and level density of 1- states in 96Mo have been extracted from a high-resolution study of the (p,p') reaction at 295 MeV and extreme forward angles. By comparison with compound nucleus $γ$ decay experiments, this allows a test of the generalized Brink-Axel hypothesis in the energy region of the Pygmy Dipole Resonance. The Brink-Axel hypothesis is commonly assumed in astrophysical reaction network calculations and states that the gamma strength function in nuclei is independent of the structure of initial and final state. The present results validiate the Brink-Axel hypothesis for 96Mo and provide independent confirmation of the methods used to separate gamma strength function and level density in $γ$ decay experiments.

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arXiv2017

Double charge exchange ($^{11}$B,$^{11}$Li) reaction for double beta decay response

The ($^{11}$B,$^{11}$Li) double charge-exchange reaction (DCER) at $E(^{11}$B)/$A$=80 MeV was measured for the first time to demonstrate the feasibility of the reaction for studying neutrino nuclear responses for double beta decays (DBD). The $^{13}$C($^{11}$B,$^{11}$Li)$^{13}$O reaction shows strengths at the ground state and low and high excitation giant resonance regions. The $^{56}$Fe ($^{11}$B,$^{11}$Li) $^{56}$Ni reaction shows the large strengths in the possible double giant resonance region and beyond, but shows no strengths in the low excitation region below 5 MeV, suggesting strong concentration of the DBD strength at the high excitation region. The DCER is used to evaluate the spin isospin strengths relevant to DBD responses.

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arXiv2016

Change of nuclear configurations in the neutrinoless double-$β$ decay of $^{130}$Te $\rightarrow$ $^{130}$Xe and $^{136}$Xe $\rightarrow$ $^{136}$Ba

The change in the configuration of valence protons between the initial and final states in the neutrinoless double-$β$ decay of $^{130}$Te $\rightarrow$ $^{130}$Xe and of $^{136}$Xe $\rightarrow$ $^{136}$Ba has been determined by measuring the cross sections of the ($d$,$^3$He) reaction with 101-MeV deuterons. Together with our recent determination of the relevant neutron configurations involved in the process, a quantitative comparison with the latest shell-model and interacting-boson-model calculations reveals significant discrepancies. These are the same calculations used to determine the nuclear matrix elements governing the rate of neutrinoless double-$β$ decay in these systems.

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arXiv2016

Competition of $β$-delayed protons and $β$-delayed $γ$ rays in $^{56}$Zn and the exotic $β$-delayed $γ$-proton decay

Remarkable results have been published recently on the $β$ decay of $^{56}$Zn. In particular, the rare and exotic $β$-delayed $γ$-proton emission has been detected for the first time in the $fp$ shell. Here we focus the discussion on this exotic decay mode and on the observed competition between $β$-delayed protons and $β$-delayed $γ$ rays from the Isobaric Analogue State.

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arXiv2015

Dipole polarizability of 120Sn and nuclear energy density functionals

The electric dipole strength distribution in 120Sn between 5 and 22 MeV has been determined at RCNP Osaka from a polarization transfer analysis of proton inelastic scattering at E_0 = 295 MeV and forward angles including 0°. Combined with photoabsorption data an electric dipole polarizability α_D(120Sn) = 8.93(36) fm^3 is extracted. The dipole polarizability as isovector observable par excellence carries direct information on the nuclear symmetry energy and its density dependence. The correlation of the new value with the well established α_D(208Pb) serves as a test of its prediction by nuclear energy density functionals (EDFs). Models based on modern Skyrme interactions describe the data fairly well while most calculations based on relativistic Hamiltonians cannot.

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arXiv2015

Probing astrophysically important states in $^{26}$Mg nucleus to study neutron sources for the $s$-Process

The $^{22}$Ne($α$,n)$^{25}$Mg reaction is the dominant neutron source for the slow neutron capture process ($s$-process) in massive stars and contributes, together with the $^{13}$C($α$,n)$^{16}$O, to the production of neutrons for the $s$-process in Asymptotic Giant Branch (AGB) stars. However, the reaction is endothermic and competes directly with the $^{22}$Ne($α,γ)^{26}$Mg radiative capture. The uncertainties for both reactions are large owing to the uncertainty in the level structure of $^{26}$Mg near the alpha and neutron separation energies. These uncertainties are affecting the s-process nucleosynthesis calculations in theoretical stellar models. Indirect studies in the past have been successful in determining the energies, $γ$-ray and neutron widths of the $^{26}$Mg states in the energy region of interest. But, the high Coulomb barrier hinders a direct measurement of the resonance strengths, which are determined by the $α$-widths for these states. The goal of the present experiments is to identify the critical resonance states and to precisely measure the $α$-widths by $α$ transfer techniques . Hence, the $α$-inelastic scattering and $α$-transfer measurements were performed on a solid $^{26}$Mg target and a $^{22}$Ne gas target, respectively, using the Grand Raiden Spectrometer at RCNP, Osaka, Japan. Six levels (E$_x$ = 10717 keV , 10822 keV, 10951 keV, 11085 keV, 11167 keV and 11317 keV) have been observed above the $α$-threshold in the region of interest (10.61 - 11.32 MeV). The rates are dominated in both reaction channels by the resonance contributions of the states at E$_x$ = 10951, 11167 and 11317 keV. The E$_x$ =11167 keV has the most appreciable impact on the ($α,γ$) rate and therefore plays an important role for the prediction of the neutron production in s-process environments.

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arXiv2015

Low-energy electric dipole response in 120Sn

The electric dipole strength in 120Sn has been extracted from proton inelastic scattering experiments at E_p = 295 MeV and at forward angles including 0 degree. Below neutron threshoild it differs from the results of a 120Sn(gamma,gamma') experiment and peaks at an excitation energy of 8.3 MeV. The total strength corresponds to 2.3(2)% of the energy-weighted sum rule and is more than three times larger than what is observed with the (gamma,gamma') reaction. This implies a strong fragmentation of the E1 strength and/or small ground state branching ratios of the excited 1- states.

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arXiv2015

Competition between $β$-delayed proton and $β$-delayed $γ$ decay of the exotic $T_z$ = -2 nucleus $^{56}$Zn and fragmentation of the IAS

A very exotic decay mode at the proton drip-line, $β$-delayed $γ$-proton decay, has been observed in the $β$ decay of the $T_z$ = -2 nucleus $^{56}$Zn. Three $γ$-proton sequences have been observed following the $β$ decay. The fragmentation of the IAS in $^{56}$Cu has also been observed for the first time. The results were reported in a recent publication. At the time of publication the authors were puzzled by the competition between proton and $γ$ decays from the main component of the IAS. Here we outline a possible explanation based on the nuclear structure properties of the three nuclei involved, namely $^{56}$Zn, $^{56}$Cu and $^{55}$Ni, close to the doubly magic nucleus $^{56}$Ni. From the fragmentation of the Fermi strength and the excitation energy of the two populated 0$^{+}$ states we could deduce the off-diagonal matrix element of the charge-dependent part of the Hamiltonian responsible for the mixing. These results are compared with the decay of $^{55}$Cu with one proton less than $^{56}$Zn. For completeness we summarise the results already published.

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arXiv2015

$β$-delayed $γ$-proton decay in $^{56}$Zn: analysis of the charged-particle spectrum

A study of the $β$ decay of the proton-rich $T_{z}$ = -2 nucleus $^{56}$Zn has been reported in a recent publication. A rare and exotic decay mode, $β$-delayed $γ$-proton decay, has been observed there for the first time in the $fp$ shell. Here we expand on some of the details of the data analysis, focussing on the charged particle spectrum.

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