Elastic properties of nuclear pasta in a fully three-dimensional geometry

Xia, C.-J.*; 丸山 敏毅; 安武 伸俊*; 巽 敏隆*; Zhang, Y.-X.*

Physics Letters B, 839, p.137769_1 - 137769_5, 2023/04

https://doi.org/10.1016/j.physletb.2023.137769

Realistic estimations on the elastic properties of neutron star matter are carried out with a large strain ( 0.5) in the framework of relativistic-mean-field model with Thomas-Fermi approximation, where various crystalline configurations are considered in a fully three-dimensional geometry with reflection symmetry. Our calculation confirms the validity of assuming Coulomb crystals for the droplet phase above neutron drip density, which nonetheless does not work at large densities since the elastic constants are found to be decreasing after reaching their peaks. Similarly, the analytic formulae derived in the incompressible liquid-drop model give excellent description for the rod phase at small densities, which overestimates the elastic constants at larger densities. For slabs, due to the negligence on the variations of their thicknesses, the analytic formulae from liquid-drop model agree qualitatively but not quantitatively with our numerical estimations. By fitting to the numerical results, these analytic formulae are improved by introducing dampening factors. The impacts of nuclear symmetry energy are examined adopting two parameter sets, corresponding to the slope of symmetry energy L = 41.34 and 89.39 MeV. Even with the uncertainties caused by the anisotropy in polycrystallines, the elastic properties of neutron star matter obtained with L = 41.34 and 89.39 MeV are distinctively different, results in detectable differences in various neutron star activities.

Nuclear pasta structures and symmetry energy

Xia, C.-J.*; 丸山 敏毅; 安武 伸俊*; 巽 敏隆*; Zhang, Y.-X.*

Physical Review C, 103(5), p.055812_1 - 055812_13, 2021/05

https://doi.org/10.1103/PhysRevC.103.055812

In the framework of the relativistic mean field model with Thomas-Fermi approximation, we study the structures of low density nuclear matter in a three-dimensional geometry with reflection symmetry. The effect of finite cell size is treated carefully by searching for the optimum cell size. Typical pasta structures (droplet, rod, slab, tube, and bubble) arranged in various crystalline configurations are obtained for both fixed proton fractions and -equilibration. It is found that the properties of droplets/bubbles are similar in body-centered cubic (BCC) and face-centered cubic (FCC) lattices, where the FCC lattice generally becomes more stable than BCC lattice as density increases. For the rod/tube phases, the honeycomb lattice is always more stable than the simple one. By introducing an - cross coupling term, we further examine the pasta structures with a smaller slope of symmetry energy MeV, which predicts larger onset densities for core-crust transition and non spherical nuclei. Such a variation due to the reduction of is expected to have impacts on various properties in neutron stars, supernova dynamics, and binary neutron star mergers.

Sorption and diffusion of Cs in Horonobe-URL's sedimentary rock; Comparison and model prediction of retardation parameters from sorption and diffusion experiments

舘 幸男; 清田 佳美; 土井 玲祐; Xia, X.*; 油井 三和

Materials Research Society Symposium Proceedings, Vol.1124, p.573 - 579, 2009/00

Diffusion and sorption of Cs in the sedimentary rock of Horonobe generic URL site were studied in the present study. The retardation parameters, De and Kd, of rock for Cs were measured by both batch sorption and intact diffusion experiments with the comparison of obtained retardation parameters each other. The tracer depletion, breakthrough and inner concentration data in the through diffusion experiment were simulated simultaneously by the conventional transport model with one set of the retardation parameters. The Kd values obtained from the data fitting were consistent with those obtained by the batch sorption experiment with crushed rock. The obtained sorption parameters were also simulated based on geochemical model calculation to interpret the sorption behavior theoretically under the assumption of dominant sorption minerals and their sorption mechanism.

幌延堆積岩へのCs収着挙動に対するイオン交換反応に基づくモデルの適用性検討

土井 玲祐; Xia, X.*; 柴田 雅博; 北村 暁; 吉川 英樹

JAEA-Research 2007-007, 21 Pages, 2007/03

JAEA-Research-2007-007.pdf:1.57MB

高レベル放射性廃棄物の地層処分システムの性能評価に対する信頼性向上の観点から、地層処分環境下での放射性核種等の移行評価が重要である。収着は核種移行を遅延させる主要なメカニズムの一つであり、その指標として分配係数(K)が用いられる。地層処分システムの性能評価において、このKの予測が不可欠で、その予測方法の確立が必要である。本研究では、Cs収着が試料中のイライトにおけるイオン交換反応に支配されるというモデルを幌延堆積岩へのCs収着試験結果に対して適用し、このモデルの適用可能性を検討した。イライトへの収着に関してCsと競争する陽イオン(K, NH, Na)とのイオン交換反応に基づき、平衡時の液中Cs濃度をモデルに基づく計算により求めることでKを算出した。このKについて実験値とモデル計算値で比較した。KのCs濃度依存性については、平衡Cs濃度が高くなるとK値が減少する実験結果をモデル計算で説明できた。しかし、Kの実験値と計算値には一桁程度の差が認められた。