arXiv subjects

Naohiko Otuka

Publications and source records attributed to Naohiko Otuka.

9 recordsLinked to original sources

arXiv2026

Modernization in processing and dissemination of experimental cross section data in EXFOR

The EXFOR library is a nearly complete database for experimental radionuclide production cross sections for light charged-particle induced reactions, and retrieval of the experimental cross sections in EXFOR is the first step in determination of the best estimate of the radionuclide production cross section. The EXFOR format was designed with 80-column punched cards as the recording media, but the format is still preferred for compilation and exchange of the nuclear reaction data. The format is suitable for reading and processing by EXFOR compilers, but it is not a good choice for reading by EXFOR users with modern computer languages such as Python. We have recently attempted to lower the barrier for modern software engineers to access the information stored in the EXFOR by developing tools converting an EXFOR file to (1) the HTML format for human reading (X4IVEW), and (2) the CX4 (Compact EXFOR) format for tabulation and plotting (X4TOCX). This article introduces X4VIEW and a preliminary version of X4TOCX with the radionuclide production cross section as an example.

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arXiv2026

Influence of secondary neutrons on alpha-particle induced reaction cross section measurement below the Coulomb barrier

The influence of the secondary neutrons on measurements of alpha-particle activation cross sections below the Coulomb barrier was studied for the $^\mathrm{nat}$Pt($α$,x)$^\mathrm{195m}$Pt reaction. We characterized the secondary neutron field by using the particle transport simulation code PHITS, and estimated the $^\mathrm{nat}$Pt(n,x)$^\mathrm{195m}$Pt yields by using the characterized neutron spectra and the $^\mathrm{nat}$Pt(n,x)$^{195m}$Pt cross sections in the JENDL-5/A library. We confirmed that the unexpectedly high $^\mathrm{nat}$Pt($α$,x)$^\mathrm{195m}$Pt cross sections below the Coulomb barrier measured by us are explained well by the $^\mathrm{nat}$Pt(n,x)$^\mathrm{195m}$Pt reaction induced by the secondary neutrons. This indicates that the secondary neutron effect is sometimes not negligible even in low energy charged-particle activation cross section measurements. We also studied the influence of the secondary light charged particles by the same approach, and confirmed that their influence is negligible.

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arXiv2025

Energy dependence of isomeric ratios for alpha-particle-induced reactions on natural platinum up to 50 MeV studied by simultaneous decay curve analysis

The isomeric ratios and cross sections were measured up to 50 MeV for production of $^{198m,g}$Au, $^{197m,g}$Hg, $^{195m,g}$Hg and other Hg, Au and Pt radionuclides in irradiation of natural platinum by alpha-particles using the stacked foil activation technique and offline gamma-ray spectrometry. The simultaneous decay curve analysis was applied to the emission rates of more than 40 gamma lines to directly derive the independent cross sections of all products without determining the cumulative cross sections. The measured cross sections and isomeric ratios were compared with those compiled in the EXFOR library and simulated by TALYS-2.0. We found that the $^{nat}$Pt($α$,x)198g+mAu, $^{197g+m}$Hg and $^{195g+m}$Hg cross sections are fairly reproduced by the simulation, while the simulation result requires adjustment of the spin cutoff parameter for better reproduction of the isomeric ratios.

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arXiv2025

EXFOR utility codes (ForEXy) and their application to neutron fission cross section evaluation

We developed a set of EXFOR utility codes (ForEXy) to process the information of the experimental nuclear reaction data stored in the EXFOR library. We designed a new JSON format (J4) for the EXFOR library, and developed a code converting the information in an EXFOR file to a J4 file (X4TOJ4) and another code converting it to an EXFOR file (J4TOX4) as a core part of this new code package. We also developed some other codes for managements of the EXFOR storage, bibliography and dictionary. As an application of the new code package, we constructed covariance matrices for the fast neutron induced fission cross sections of neptunium-237 in the EXFOR library by using the new codes, and applied them to evaluation of the cross section between 100 keV and 200 MeV.

physics.comp-ph↗

arXiv2024

Evaluation of uranium-233 neutron capture cross section in keV region

The uranium-233 neutron capture cross section between 3 keV and 1 MeV was evaluated with the new alpha value recently measured at the Los Alamos National Laboratory LANCE facility and compiled in the EXFOR library. The obtained capture cross section is systematically lower than those in the latest versions of the major general purpose nuclear data libraries, and the reduction from the JENDL-5 library is close to 50% around 20 keV. The newly evaluated cross section was benchmarked against 166 criticality experiments chosen from the ICSBEP handbook by performing Monte Carlo neutron transport calculation with the JENDL-5 library, and slight reduction of the cumulative chi-square value was achieved by adoption of the newly evaluated capture cross section.

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arXiv2024

Isomer production studied with simultaneous decay curve analysis for alpha-particle induced reactions on natural platinum up to 29 MeV

The isomeric ratios of $^{198}$Au, $^{197}$Hg and $^{195}$Hg produced by $α$-particle induced reactions on natural platinum were investigated experimentally up to 29 MeV by using the standard stacked foil activation technique and $γ$-ray spectrometry. The isomeric ratios of $^{197}$Hg and $^{195}$Hg determined by the conventional activation cross section formula showed strong cooling time dependence. The time dependence was resolved by adjusting the isomeric transition branching ratios for the two isotopes within a simultaneous decay curve analysis framework. Our analysis suggests 94.5$\pm$0.7% and 48.9$\pm$1.8% as the isomeric transition branching ratios of $^{197m}$Hg (24 h) and $^{195m}$Hg (42 h), respectively. The isomeric ratios and independent production cross sections of $^{198}$Au, $^{197}$Hg, $^{195}$Hg and some other Hg, Au and Pt isotopes were also measured down to 6 MeV with these corrected isomeric transition branching ratios, and compared with predictions of statistical and pre-equilibrium models by TALYS-2.0 to discuss spin cuto? parameter dependence. We found the measured isomeric ratios are better predicted if we reduce the spin cuto? parameter to half or less from that estimated with the rigid body moment of inertia.

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arXiv2023

EXFOR-based simultaneous evaluation for neutron-induced fission cross section of plutonium-242

The $^{242}$Pu neutron-induced fission cross section was evaluated from 100 keV to 200 MeV. The experimental $^{242}$Pu and $^{235}$U fission cross sections and their ratios in the EXFOR library were reviewed and analysed by the least-squares method. Additional simultaneous evaluation was performed by including the experimental database of the $^{233,238}$U and $^{239,240,241}$Pu fission cross sections and their ratios developed for JENDL-5 evaluation. The $^{242}$Pu fission cross sections from our evaluation and JENDL-5 evaluation are close to each other below 1 MeV while systematically differ from each other above 10 MeV. The cross section from our evaluation is systematically lower than the JENDL-4.0 cross section in the prompt fission neutron spectrum peak region ($\sim$5% lower around 1 MeV). The newly evaluated $^{242}$Pu fission cross section was verified against the cross section measured in the $^{252}$Cf spontaneous fission neutron field and criticalities of small-sized LANL fast systems, and demonstrated better performance than the JENDL-4.0 cross section on the same level with the JENDL-5 cross section.

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arXiv2023

EXFOR-based simultaneous evaluation for fast neutron-induced fission cross section of thorium-232

The $^{232}$Th neutron-induced fission cross section was evaluated from 500 keV to 200 MeV. The experimental $^{232}$Th fission cross sections and their ratios to the $^{235,238}$U fission cross sections in the EXFOR library were reviewed and analysed by the least-squares method. The newly published $^{232}$Th/$^{235}$U fission cross section ratios from the time-of-flight measurements at the CERN n_TOF and CSNS Back-n facilities were compiled in EXFOR. Additional simultaneous evaluation was performed by including the experimental $^{233,238}$U and $^{239,240,241}$Pu fission cross sections and their ratios. The new evaluation provides the $^{232}$Th fission cross section systematically lower than the JENDL-5 cross section. The reduction is 4% in the plateau region between 2 and 6 MeV and more significant in the subthreshold fission region. The present evaluation reduces the $^{232}$Th fission cross section averaged over the $^{252}$Cf spontaneous fission neutron spectrum from the JENDL-5 evaluation by 4%, which is closer to the other general purpose libraries but underestimates Grundl et al's measurement by 11%.

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arXiv2022

EXFOR-based simultaneous evaluation of neutron-induced uranium and plutonium fission cross sections for JENDL-5

The neutron-induced fission cross sections were simultaneously evaluated for the JENDL-5 library for $^{233,235}$U and $^{239,241}$Pu from 10 keV to 200 MeV and for $^{238}$U and $^{240}$Pu from 100 keV to 200 MeV. Evaluation was performed by least-squares fitting of Schmittroth's roof function to the logarithms of the experimental cross sections and cross section ratios in the EXFOR library. A simultaneous evaluation code SOK was used with its extension to data in arbitrary unit. The outputs of the code were adopted as the evaluated cross sections without any further corrections. The newly obtained evaluated cross sections were compared with the evaluated cross sections in the JENDL-4.0 library and the IAEA Neutron Data Standards 2017. The evaluated cross sections were also validated against the californium-252 spontaneous fission neutron spectrum averaged cross sections, $ΣΣ$ (coupled thermal/fast uranium and boron carbide spherical assembly) neutron spectrum averaged cross sections, and small-sized LANL fast system criticalities. The changes in the obtained evaluated cross sections from those in the JENDL-4.0 library are within 4% ($^{241}$Pu), 3% ($^{233}$U, $^{240}$Pu), or 2% ($^{235}$U, $^{239}$Pu). The newly evaluated $^{235}$U, $^{238}$U and $^{239}$Pu cross sections agree with the IAEA Neutron Data Standards 2017 within 2% with some exceptions.

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