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Kunieda, Satoshi; Furutachi, Naoya; Minato, Futoshi; Iwamoto, Nobuyuki; Iwamoto, Osamu; Nakayama, Shinsuke; Ebata, Shuichiro*; Yoshida, Toru*; Nishihara, Kenji; Watanabe, Yukinobu*; et al.

Journal of Nuclear Science and Technology, 56(12), p.1073 - 1091, 2019/12

Times Cited Count：1 Percentile：50.57(Nuclear Science & Technology)A new nuclear data library, JENDL/ImPACT-2018, is developed for an innovative study on the transmutation of long-lived fission products. Nuclear reaction cross- sections are newly evaluated for incident neutrons and protons up to 200 MeV for 163 nuclides including long-lived nuclei such as Se, Zr, Pd and Cs. Our challenge is an evaluation of cross-sections for a number of unstable nuclei over a wide energy range where the experimental data are very scarce. We estimated cross- sections based on a nuclear model code CCONE that incorporates an advanced knowledge on the nuclear structure theory and a model-parameterization based on a new experimental cross-sections measured by the inverse kinematics. Through comparisons with available experimental data on the stable isotopes, it is found that the present data give predictions of cross-sections better than those in the existing libraries.

Furutachi, Naoya; Minato, Futoshi; Iwamoto, Osamu

Physical Review C, 100(1), p.014610_1 - 014610_7, 2019/07

Times Cited Count：0 Percentile：100(Physics, Nuclear)We investigated the probability distribution of thermal neutron capture cross sections () deduced stochastically with the resonance parameters randomly sampled from Wigner and Porter-Thomas distributions. We found that the typical probability distribution has an asymmetric shape. While there is a long tail on the large side due to a resonance happening to be close to the thermal energy, the multiresonance contribution considerably reduces the probability on the small side. We also found that the probability distributions have a similar shape if nuclei have an average resonance spacing sufficiently larger than an average radiation width. We compared the typical probability distribution with the distribution of the experimental values of 193 nuclei and found a good agreement between them.

Furutachi, Naoya*; Minato, Futoshi; Iwamoto, Osamu

Journal of Nuclear Science and Technology, 56(5), p.412 - 424, 2019/05

Times Cited Count：2 Percentile：26.15(Nuclear Science & Technology)A phenomenological level density model that has different level density parameter sets for the state densities of the spherical and the deformed states, and the optimization of the parameters using the 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 shows 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.

Nakayama, Shinsuke; Furutachi, Naoya; Iwamoto, Osamu; Watanabe, Yukinobu*

Physical Review C, 98(4), p.044606_1 - 044606_8, 2018/10

Times Cited Count：6 Percentile：21.88(Physics, Nuclear)Use of deuteron-induced spallation reactions at intermediate energies has recently been proposed for transmutation of several long-lived fission products (LLFPs). In the design study of a transmutation system using a deuteron primary beam, accurate cross section data of deuteron-induced reactions on the LLFPs are indispensable. In the present study, production cross sections of residual nuclei in the deuteron-induced reactions on Zr and Pd at MeV/nucleon are analyzed using DEURACS, in which the breakup processes are explicitly taken into account. The calculated values reproduced the experimental data quantitatively well. From a component-by-component analysis, it was found that the components of nucleon absorption make the significant contributions to residual nuclei production. This result strongly indicates that consideration of the breakup processes is essentially important to predict production of residual nuclei in deuteron-induced reactions.

Minato, Futoshi; Iwamoto, Osamu; Minomo, Kosho*; Ogata, Kazuyuki*; Iwamoto, Nobuyuki; Kunieda, Satoshi; Furutachi, Naoya

EPJ Web of Conferences (Internet), 146, p.12032_1 - 12032_4, 2017/09

Times Cited Count：1 Percentile：23.47Phenomenological optical potential is known to be able to describe the elastic scattering process. It is applied widely to the nuclear data evaluation of the cross section. Many kinds of the optical potential have been studied so far. However, the parameters in the phenomenological optical potentials are determined so as to reproduce existing experimental data, so that use of it for unmeasured nuclei such as neutron-rich nuclei is not necessarily reliable. Recently, a new optical potential derived from the microscopic effective reaction theory (MERT) was proposed. Since the formulation of MERT is based on the NN effective interaction, any parameterizations in the optical potential aren't needed. Therefore, it is capable of calculating nuclei whose scattering cross section isn't measured. We incorporate the optical potentials of MERT in code CCONE and start nuclear data evaluation of several nuclei. In this work, we discuss difference of cross sections evaluated by MERT's optical potentials and conventional phenomenological ones.

Furutachi, Naoya; Minato, Futoshi; Iwamoto, Osamu

JAEA-Conf 2016-004, p.93 - 98, 2016/09

To investigate feasibility of the nuclear transmutation of long-lived fission products (LLFPs), nuclear data used in the simulation calculation of transmutation system is essential. To improve the precision of simulation calculation, the nuclear data of various nuclei produced via nuclear transmutation of LLFPs involved in the simulation is also important. Since wide range of nuclei are expected to be produced depends on the method of transmutation, and there are no available experimental data for some of them, a systematic information based on a microscopic calculation is desirable. In this work, we have performed microscopic nuclear structure calculation to derive the structure parameters used in the nuclear data evaluation. We have calculated deformation parameters and ground-state spin and parities for Z = 30-55 medium nuclei including odd-even and odd-odd nuclei, expected to be produced via the transmutation of Se, Zr, Pd and Cs, using Hartree-Fock-Bogoliubov (HFB) theory. The calculation was done by HFBTHO code. The results are compared with the available experimental data, and reliability of the prediction with the present method is discussed.

Furutachi, Naoya; Minato, Futoshi; Iwamoto, Osamu

no journal, ,

To establish the nuclear transmutation system for the long-lived fission products (LLFPs), it is desired to improve precision of the simulation calculation for the transmutation system. To achieve this, nuclear data of various nuclei produced via the nuclear transmutation of LLFPs are also important. However, it is expected that unstable nuclei with no available experimental data are produced via the nuclear transmutation. One of the physical quantity that is very difficult to predict with no experimental data is the thermal neutron capture cross section. The thermal neutron capture cross section is dominated by the energy and width of the first resonance, and slight variation of them can change the thermal neutron capture cross section drastically. While it is very difficult to determine them with high precision, it is known that a resonance width follows Porter-Thomas distribution because of complexity and randomness of a nuclear structure, and a resonance spacing follows Wigner distribution. In this work, we calculate the thermal neutron capture cross section by using the statistical property of the resonance parameters with Monte Carlo method. The calculation result is obtained as a probability distribution of the thermal neutron capture cross section. We calculated approximately 250 nuclei that have experimental data, and found that the dispersion of the experimental data is well explained by the calculated probability distribution.

Furutachi, Naoya; Minato, Futoshi; Iwamoto, Osamu

no journal, ,

For the feasibility study of the nuclear transmutation system for the long-lived fission products(LLFPs), the simulation calculation to estimate the efficiency of the transmutation system is essential. The precision of the simulation calculation largely depends on the evaluated nuclear data used in the calculation. To improve the precision of the simulation calculation, developing nuclear data not only of LLFPs but also of all the nuclei involved in the simulation calculation is desirable. When we study the transmutation system using the nuclear reaction such as spallation reaction, it is anticipated that a wide range of nuclei including unstable nuclei with no or scarce experimental are produced. In particular, the shortage of nuclear experimental data in resonance region is a problem for nuclear data evaluation, because it is difficult to predict the resonant structure precisely in a theoretical way. One of the methods mitigating this problem is to use the resonance parameters randomly determined from the statistical properties of the resonance parameters. This approach is already adopted in TENDL nuclear data library. However, the cross section calculated using such a method would have a large uncertainty arising from the statistical fluctuation of the resonance parameters in principle. This uncertainty wasn't discussed in the previous study. In this study, we investigated the statistical method to predict the nuclear reaction data in resonance region focusing on its statistical uncertainties. Particularly, we shall discuss the neutron capture cross sections of nuclei expected to be produced via the transmutation of Se-79, Zr-93, Pd-107 and Cs-135.

Furutachi, Naoya; Minato, Futoshi; Iwamoto, Osamu

no journal, ,

The nuclear level density is essential for nuclear reaction calculations using the statistical model and pre-equilibrium models. Phenomenological Fermi gas models have been used widely for calculations of the nuclear level density, however, reliability of them depend on the parameter adjustment to reproduce the experimental informations of the s-wave neutron resonance spacing D0, and therefore, calculations using more microscopic models are desirable for unstable nuclei that have no available experimental information. The microscopic statistical models and combinatorial models based on Hartree-Fock theory are models that can reproduce the experimental D0 with precisions comparable to the phenomenological models. However, these calculations are strongly dependent on the strength of the pairing interaction, and its uncertainty affect to the precision of the calculations. Therefore, in this work, we improved the treatment of the pairing interaction in the nuclear structure calculation, and analyzed how the pairing interaction affect to the precision of the nuclear level density calculation.

Furutachi, Naoya; Minato, Futoshi; Iwamoto, Osamu

no journal, ,

Nuclear reaction calculations using the statistical model require information of the nuclear level density. While the phenomenological models such as Fermi Gas model are often used to calculate the nuclear level density in usual nuclear data evaluations, reliability of such level density depends on parameter adjustments using experimental values. Therefore, development of microscopic calculation methods that does not depend on parameter adjustments is desired. One of the microscopic methods to calculate the nuclear level density is the combinatorial method that uses single-particle levels obtained from Hartree-Fock theory, and its reliability has been discussed through the reproducibility of the s-wave neutron resonance spacing . However, comparisons of cross sections with experiments are only preformed for (n,) reaction of some nuclei, and is still insufficient. Therefore, in this work, we calculate the nuclear level density using the combinatorial method, and apply it to the nuclear reaction calculations such as (n,) reaction and (n,2n) reaction calculations. The cross sections of these reactions adding to the s-wave neutron resonance spacing for stable nuclei are compared with the experiments systematically, and then the reliability of the nuclear level density is discussed.

Furutachi, Naoya; Minato, Futoshi; Iwamoto, Osamu

no journal, ,

While Fermi Gas type phenomenological models are widely used to calculate the nuclear level density (NLD) of stable nuclei, it is important to develop a microscopic method to achieve reliable NLD for unstable nuclei. One of microscopic methods to calculate NLD is that based on the microscopic nuclear structure calculation using Hartree-Fock-Bogoliubov (HFB) theory. Since a effective nuclear interaction is basically the only input in HFB calculation, we investigated how the calculated NLD depends on it with special attention to the adopted pairing interaction, to discuss about the reliability of this method. Adding to SkM* force that was used in our previous study, SLy4, SkP, and UNEDF1 forces were used in HFB calculations of the present study. The statistical method was applied to derive NLD based on HFB calculation. We compared the s-wave resonance spacing D derived from the calculated NLD with the experiments, and found better agreement with the results with SkP and UNEDF1 forces compared to those with SkM and SLy4 forces.

Iwamoto, Osamu; Minato, Futoshi; Furutachi, Naoya; Iwamoto, Nobuyuki; Kunieda, Satoshi

no journal, ,

Under the ImPACT program of nuclear transmutation, we are developing a new nuclear data library that includes nuclear data of 4 main LLFPs (Se, Zr, Pd, Cs) and surrounding nuclei. To improve accuracy of nuclear data for unstable nuclei whose experimental data are scarce, microscopic nuclear structure theories was used to deduce nuclear level density and -ray strength function. They were applied to evaluation of cross sections for neutron and proton induced reactions up to 200 MeV. Status of development of the library including evaluation methods and results is reported.

Furutachi, Naoya; Minato, Futoshi; Iwamoto, Osamu

no journal, ,

To establish a reasonable nuclear transmutation technology for long-lived fission products (LLFPs), it is important to improve precision of the nuclear data needed for the simulation of the nuclear transmutation. The level density is essential for the nuclear reaction calculation using the statistical model, and it has significant influence on the precision of the nuclear data evaluation. Although a phenomenological model such as Fermi Gas model is used in a usual nuclear data evaluation, it is considered that using a microscopic theory that has predictive power superior to a phenomenological model brings better precision for the nuclear data. In this study, to improve precision of the nuclear data of LLFPs and nuclei around LLFPs, the level densities needed for the nuclear data evaluation of those nuclei were derived based on the microscopic nuclear data calculation. In this derivation, we improved the calculation method to describe prcisely the effect of the deformation change with nuclear excitation. To analyze precision of the nuclear reaction calculation, we compared the cross sections of various reaction channel systematically with the experimental data of stable nuclei.

Furutachi, Naoya; Minato, Futoshi; Iwamoto, Osamu

no journal, ,

no abstracts in English

Furutachi, Naoya; Minato, Futoshi; Iwamoto, Osamu

no journal, ,

Except for extremely light nuclei and neutron rich nuclei, generally the density of nuclear excited states around neutron threshold energy is very high, and therefore it is very difficult to predict energy and width of resonance precisely. On the other hand, it has been known that the resonance parameters have statistical property with high density of excited states. There is a theoretical method to calculate cross section in resonance region by generating resonance parameters randomly utilizing the statistical properties of the resonance parameters. Such a method can reflect a theoretical information of resonance on a nuclear data evaluation for nuclei with no experimental data, such as fission products. However, studies for how to determine a representative value of the cross section randomly calculated, and what is an uncertainty from the randomness, are insufficient. Therefore, in this study, we calculated the cross section in the resonance region using randomly generated resonance parameters, and derived the probability distribution of the cross section by calculating cross section repetitively using resonance parameter sets generated from different random seeds. By using this density distribution, we discuss the behavior of the statistically reasonable cross section, and uncertainty from statistical fluctuation.

Nakayama, Shinsuke; Furutachi, Naoya; Iwamoto, Osamu; Watanabe, Yukinobu*

no journal, ,

In the ImPACT project, deuteron is a first candidate of incident beam for nuclear transmutation of long-lived fission products (LLFPs) and accurate deuteron nuclear data on LLFPs are strongly required. Thus, we have performed theoretical model analysis of deuteron-induced spallation reactions on LLFP with DEURACS, which is the computational code dedicated for deuteron-induced reactions. Through comparison with measured data and other calculation method, the applicability of DEURACS to spallation reactions and the role of breakup processes in the reactions will be discussed.

Kunieda, Satoshi; Furutachi, Naoya*; Minato, Futoshi; Iwamoto, Nobuyuki; Nakayama, Shinsuke; Iwamoto, Osamu

no journal, ,

no abstracts in English

Iwamoto, Osamu; Kunieda, Satoshi; Furutachi, Naoya*; Minato, Futoshi; Iwamoto, Nobuyuki; Nakayama, Shinsuke; Ebata, Shuichiro*; Nishihara, Kenji; Yoshida, Toru*; Watanabe, Yukinobu*; et al.

no journal, ,

Treatment of high-level radioactive wastes produced by reactor operation is are very important problem for nuclear energy. A new nuclear data library JENDL/ImPACT-2018 has been developed as a part of the ImPACT project aiming at reduction and resource recycling of LLFPs through nuclear transmutation. Due to possible creation of a lot of secondary products including unstable nuclei, the nuclear reaction data have been evaluated with improving predictability of theoretical calculations.