九大原子核セミナー

2018年11月27日(火) 16:30〜18:00

講師： Miguel Maeques 氏 (GANIL)
演題：First observation of the heaviest Boron and Nitrogen isotopes
場所：ウェスト1号館7階 物理セミナー室3 (W1-A-723室)

概要：
The well-established shell structure of the nucleus, that translates into an enhanced stability for systems with a magic number of protons and/or neutrons (2, 8, 20...), is distorted when nuclei approach the landscape limits or driplines, specially the more distant one, the neutron dripline. The most spectacular effect is found at neutron number N=16, in what is known as the oxygen anomaly: while oxygen can hold at most 16 neutrons, the next element, fluorine, can hold up to 22. In this respect, the neutron-rich tail of the boron and nitrogen isotopic chains are of particular importance. 21B is the first isotope beyond the dripline at N=16, and 24,25N represent one step further from the already exotic isotopes 25,26O.
In this seminar we will review the results from experiments performed at the Radioactive Isotope Beam Factory (RIBF) of the RIKEN Nishina Center, in which the most neutron-rich boron and nitrogen isotopes to date, 20,21B and 24,25N, have been observed for the first time using invariant-mass spectroscopy following one- or two-proton removal reactions from, respectively, 22N, 22C and 26,27F at energies around 230 MeV/nucleon. Their unbound nature lead to the decay into 19B or 23N plus one or two neutrons. Through a comparison with shell-model calculations and extrapolated values from mass evaluations, the results will be discussed in terms of the prevalence of the N=16 shell gap at Z<8.

2018年10月19日(金) 16:30〜18:00

講師： 鷲山 広平 氏 (九州大学)
演題：Fusion hindrance in heavy nuclear systems with time-dependent Hartree-Fock

場所：ウェスト1号館7階 物理セミナー室2 (W1-A-722室)

概要：
The interplay between static and dynamical effects in nuclei is crucial for appropriate description of heavy-ion fusion reactions at energies around the Coulomb barrier. Coupled-channels calculations have been widely used to quantitatively describe the entrance channel of fusion reactions in light- and medium-mass systems, whose charge product (ZpZt) is less than 1600. In heavy systems (ZpZt >1600), it was observed that the fusion probability is strongly hindered around the Coulomb barrier, compared with light and medium-mass systems and with coupled-channels calculations. This phenomenon is called fusion hindrance. Quasi-fission process is considered to be mostly responsible for this hindrance. I address this problem by microscopic time-dependent Hartree-Fock (TDHF) model. I will show the analysis of fusion hindrance from head-on collision simulations of TDHF. Then, I will show recent progress of quasi-particle random-phase approximation in three-dimensional space. This will be used to compute mass parameters along fission paths.