九大原子核セミナー

2010年10月29日(金) 16:00

講師：M. K. Gaidarov 氏(Bulgarian Academy of Sciences)
演題：Probing Nuclear Structure of Exotic Nuclei and
Reactions with Helium Isotopes
場所：理学部・物理・第三講義室(理学部2号館2階2249室)

概要：
An investigation of important characteristics of nuclear structure near drip-lines in coordinate and momentum space has been performed. Results on charge form factors calculations for several unstable neutron-rich isotopes of light (He, Li), medium (Ni), and heavy nuclei (Kr, Sn) are presented and compared to those of stable isotopes in the same isotopic chain. For the lighter isotopes the proton and neutron densities are obtained within a microscopic large-scale shell model, while for heavier ones the densities are calculated in the framework of deformed self-consistent mean field Skyrme HF+BCS method. The resulting charge radii and neutron skin thicknesses of even-even isotopes of Ni, Kr, and Sn are compared with available experimental data, as well as with other theoretical predictions. The formation of a neutron skin, which manifests itself in an excess of neutrons at distances greater than the radius of the proton distribution, is analyzed in terms of various defnitions. Formation of a proton skin is shown to be unlikely. The nucleon momentum distributions for the same isotopic chains of neutron-rich nuclei (Ni, Kr, and Sn) are studied in the framework of the same mean-field method, as well as of theoretical correlation methods based on light-front dynamics and local density approximation in which nucleon-nucleon (NN) correlations at short distances are taken into account. The isotopic sensitivities of the calculated neutron and proton momentum distributions are investigated together with the effects of pairing and NN correlations. The effects of deformation on both the neutron skins and momentum distributions in even-even deformed nuclei far from the stability line are discussed.

A microscopic approach to calculate the optical potential (OP) with the real part obtained by a folding procedure and with the imaginary part inherent in the high-energy approximation is applied to study the 6,8 He+p and 6 He+ 12 C elastic scattering data at energies of tens of MeV/nucleon (MeV/N). The calculated optical potentials and cross sections are based on different models for the neutron and proton density distributions of 6,8 He and that obtained from the electron scattering form factors for 12 C. The role of the spin-orbit potential and effects of the energy and density dependence of the effective NN forces are studied. Comparison of the calculations with the available experimental data on the elastic scattering differential cross sections at beam energies < 100 MeV/N is performed. The problem of ambiguity of adjusted optical potentials is resolved requiring the respective volume integrals to obey the determined dependence on the collision energy. Estimations of the Pauli blocking effects on the optical potentials and cross sections are also given and discussed. It is shown that the present approach, which uses only parameters that renormalize the depths of the OP, can be applied along with other methods like that from the microscopic g-matrix description of the complex proton optical potential. Conclusions on the role of the aforesaid effects and on the mechanism of the considered processes are made.

2010年10月22日(金) 16:00

講師：米山　博志 氏(佐賀大学)
演題：有限温度・有限密度におけるQCD臨界点近傍の特異性
場所：理学部・物理・第三講義室(理学部2号館2階2249室)

概要：
有限温度・有限密度QCDの相図の決定は、重イオン反応実験の進展とも相まって重要な研究テーマになっている。特に、QCD臨界点については様々の方法によってその存在が予言されているが、格子ゲージ理論による数値的検証は深刻な符号問題のために確定的段階にいたっていない。
格子ゲージ理論ではこの符号問題を回避するために、テーラー展開法や虚数化学ポテンシャル法などの方法が用いられているが、これらの方法の有効性は複素化学ポテンシャル平面におけるsingularity と関係している。このsingularity は分配関数の零点と密接に関係しており、したがって、分配関数の零点の構造を見ることにより、これら方法の有効性を調べることが可能になる。また分配関数の零点の研究は、臨界現象の理解にたいして通常の方法とは相補的な視点を提供し、その理解を深める重要な役割をしている。
本研究では、複素化学ポテンシャル平面内の、主に臨界点近傍におけるsingularityの様相に注目をし、QCDの有効理論とモンテカルロ計算を用いた計算の結果について報告をする。