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Journal Articles

Anomaly of structural relaxation in complex liquid metal of bismuth; Dynamic correlation function of coherent quasi-elastic neutron scattering

Kawakita, Yukinobu; Kikuchi, Tatsuya*; Inamura, Yasuhiro; Tahara, Shuta*; Maruyama, Kenji*; Hanashima, Takayasu*; Nakamura, Mitsutaka; Kiyanagi, Ryoji; Yamauchi, Yasuhiro*; Chiba, Kaori*; et al.

Physica B; Condensed Matter, 551, p.291 - 296, 2018/12

 Times Cited Count:8 Percentile:49.07(Physics, Condensed Matter)

There are elemental liquid metals with complex structures far from the hard sphere (HS) packing model. Liquid Bi has an asymmetric first peak in the structure factors S(Q). The pair distribution function g(r) exhibits strange distance ratio of 1:2 between the first and the second peaks. Since a HS model with two kinds of radius produces asymmetry of the main peak in S(Q), existence of short-lived covalent bonds was discussed. Contrarily, modulation of the atomic distribution by the Friedel oscillations of shielding electrons around metallic ions was discussed. To examine its bonding nature from viewpoints of dynamic correlation functions, we have measured neutron quasielastic scattering of liquid Bi by using cold disk chopper spectrometer installed at MLF of J-PARC. The van Hove function revealed that the shoulder structure located at a longer side of the first peak in g(r) exhibits a longer relaxation time than the main structures such as the first and second peaks.

Journal Articles

The r-process element abundance with a realistic fission fragment mass distribution

Chiba, Satoshi; Koura, Hiroyuki; Maruyama, Toshiki; Ota, Masahisa*; Tatsuda, Sayuki*; Wada, Takahiro*; Tachibana, Takahiro*; Sumiyoshi, Kosuke*; Otsuki, Kaori*; Kajino, Toshitaka*

AIP Conference Proceedings 1016, p.162 - 167, 2008/05

Effect of the $$beta$$-delayed fission in r-process abundance is investigated. The data base for the fission fragment mass distribution used in the r-process network calculation is constructed based on the 2-center shell model and Langevinequation. The $$beta$$-decay rates (no emissive, neutron emission and $$beta$$-delayed fission) are also newly calculated with the gross theory. The differences appeared in the final element abundance calculated with and without fission process are demonstrated and the mass region modified by the fission products is presented.

Journal Articles

Systematic study for the shell effect in the fission fragment mass distribution reptured from neutron rich nuclei

Ota, Masahisa*; Tatsuda, Sayuki*; Yamamoto, Kazuyuki*; Asano, Tomomasa*; Wada, Takahiro*; Hashizume, Kazuaki*; Sumiyoshi, Kosuke*; Otsuki, Kaori*; Kajino, Toshitaka*; Koura, Hiroyuki; et al.

Nuclear Physics A, 805(2), p.558 - 560, 2008/02

The data base for the fission fragment mass distribution used in the r-process network calculation is constructed. The differences appeared in the final element abundance calculated with and without fission process are demonstrated and the mass region modified by the fission products is presented.

Journal Articles

Fission fragment mass distribution for nuclei in the r-process region

Tatsuda, Sayuki*; Hashizume, Kazuaki*; Wada, Takahiro*; Ota, Masahisa*; Sumiyoshi, Kosuke*; Otsuki, Kaori*; Kajino, Toshitaka*; Koura, Hiroyuki; Chiba, Satoshi; Aritomo, Yoshihiro*

AIP Conference Proceedings 891, p.423 - 426, 2007/03

We investigate the fission-fragment mass distribution on about 2000 nuclides, which should have a critical impact on the r-process nucleosynthesis through fission ($$Z>85$$). The mass distribution of fission fragment is thought to be one of the most important elements on some astrophysical conditions for the theoretical estimation of the r-process abundance pattern. We calculated the potential energy surface (PES) by means of the liquid-drop model with the shell energy correction by the Two-Center shell model in 3-dimensional parameter space. We derive fission-fragment mass distribution by considering the location and the depth of the valley of PES near the saddle point and the scission point of nuclei with the use of the Langevin calculation. We determine the fission asymmetry by examining the valley depth and its location in the deformation parameter space. The consistency of our mass asymmetry with available experimental data is discussed.

Oral presentation

Systematic study of fission fragment mass distribution by a semi-empirical model

Ota, Masahisa*; Tatsuda, Sayuki*; Wada, Takahiro*; Chiba, Satoshi; Koura, Hiroyuki; Maruyama, Toshiki; Kajino, Toshitaka*; Otsuki, Kaori*

no journal, , 

We propose a systematical method to calculate the fission fragment mass distribution (FFMD) for nuclear energy and astrophysical applications. The potential energy surface (PES) of fissionable nuclei is calculated by two-center shell model taking the mass-asymmetry, fragment deformation and distance of the fragments as parameters. Then, the ratio of symmetric and asymmetric fission modes is determined in a semi-empirical way. The present model can predict FFMD for a broad range of fissionable nuclei; Z=88 to 120. We compare the present results with measured data and systematics proposed by Katakura et al.

Oral presentation

Impact of fission fragment mass distribution on r-process nucleosynthesis pattern

Chiba, Satoshi; Koura, Hiroyuki; Maruyama, Toshiki; Ota, Masahisa*; Tatsuda, Sayuki*; Wada, Takahiro*; Tachibana, Takahiro*; Kajino, Toshitaka*; Sumiyoshi, Kosuke*; Otsuki, Kaori*

no journal, , 

We introduce $$beta$$-delayed fission in r-process calculation, and investigate the difference of the abundance pattern of synthesized nuclei depending on the model of fission fragment mass distribution. We further discuss the impact of it on nucleo-cosmochronometer and possibility to restrict the physical condition of r-process sites.

Oral presentation

Time-space correlation function of liquid metals with complex static structure deduced from pulsed neutron experiment

Kawakita, Yukinobu; Kikuchi, Tatsuya*; Inamura, Yasuhiro; Tahara, Shuta*; Maruyama, Kenji*; Hanashima, Takayasu*; Nakamura, Mitsutaka; Kiyanagi, Ryoji; Yamauchi, Yasuhiro*; Chiba, Kaori*; et al.

no journal, , 

There are many polyvalent liquid metals with complex structure which cannot be reproduced by random packing model. To explain such complexity, coexistence of metallic and covalent bonds, dynamic model of short-lived covalent bonds, and quasi-crystal model where Peierls distortion still remains even in liquid phase have been proposed from structure analyses and theoretical calculations. To obtain concrete picture experimentally for complex structure, it is indispensable to measure dynamic structure with precise statistical accuracy. We performed inelastic neutron scattering of liquid bismuth by using AMATERAS installed at MLF in J-PARC and deduced its time-space correlation function. We got evidence that structure of Peierls distortion remains even in liquid by evaluating difference in relaxation time at specific atomic distances characterized by double layered structure.

Oral presentation

Structural relaxation and time-space correlation function of liquid metals with complex structure

Kawakita, Yukinobu; Kikuchi, Tatsuya*; Inamura, Yasuhiro; Tahara, Shuta*; Maruyama, Kenji*; Hanashima, Takayasu*; Nakamura, Mitsutaka; Kiyanagi, Ryoji; Yamauchi, Yasuhiro*; Chiba, Kaori*; et al.

no journal, , 

We have performed coherent quasielastic neutron scattering experiment for liquid polyvalent metals which has complicated static structure not reproduced by a hard-sphere packing model, by utilizing AMATERAS spectrometer in J-PARC. It has been considered that, for Bi and Sb, a double-layered structure originated from Peierls distortion which is seen in solid crystalline phase remains even in their liquid phases. We have succeeded in detection of such Peierls distortion structure in liquid by difference in structural relaxation time at corresponding charateristic interatomic distances in the deduced time-space correlation function.

Oral presentation

Real time and real space analysis for atomic dynamics in liquids

Kawakita, Yukinobu; Kikuchi, Tatsuya*; Inamura, Yasuhiro; Tahara, Shuta*; Maruyama, Kenji*; Hanashima, Takayasu*; Nakamura, Mitsutaka; Kiyanagi, Ryoji; Yamauchi, Yasuhiro*; Chiba, Kaori*; et al.

no journal, , 

We have developed analysis method to reduce the so-call van Hove function, a time-space correlation function, through the regularization method for coherent quasielastic neutron scattering (QENS) of liquids. In principle, the van Hove function in r-t space can be obtained by double Fourier transform from dynamic structure factor in Q-E space. Instead of a direct function estimation of the van Hove function through the regularization method which easily involves systematical deviation of the calculated dynamic structure factor from the experimental dynamic structure factor, we used a mediation function between them and estimated it through the regularization method. We will discuss with the properties of the mediation function and the obtained van Hove function and the calculated dynamic structure factor with an example of liquid metals with complex static structure such as Bi and Sb whose QENS were measured by AMATERAS spectrometer in J-PARC.

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