Speaker
Description
The equation of state of nuclear matter(EOS), which describes the macroscopic properties of nuclei, is essential not only to describe the structure and collisions of nuclei but also to understand the astrophysical problems, such as the mechanism of supernova explosions and the structure of neutron stars. Since nuclear matter is composed of two Fermi particles, protons and neutrons, the equation of state has a term that depends on the density difference between the two, which is called the symmetry energy. From previous studies, it is known that the first-order density dependence of the symmetry energy is closely related to the thickness of the neutron skin [1].
In this study, interaction cross sections ${\sigma}_{\rm{I}}$ and charge changing cross sections ${\sigma}_{\rm{CC}}$ for $^{58-77}$Ni on a carbon target at 260 MeV/nucleon have been measured to derive matter radii and charge radii respectively. Recently, the charge radii of Ni isotopes up to mass number 70 were measured by isotope shift method [2]. In order to derive the neutron skin thickness in the more neutron-rich region, we attempted to derive the charge radii from charge changing cross section measurements. The experiment was performed at the Radioactive Isotope Beam Factory(RIBF) at RIKEN by using the BigRIPS fragment separator. The present ${\sigma}_{\rm{I}}$ data are the first systematic ones along the isotopic chain in Ni mass region.
In the neutron-rich region of Ni isotopes, the present ${\sigma}_{\rm{I}}$, for example, for $^{72}$Ni is largely enhanced in comparison with the Glauber calculation using the nucleon densities based on the systematics of stable nuclei, but is well reproduced with matter radii of Hartree-Fock calculations [3]. And the present ${\sigma}_{\rm{CC}}$ for $^{72}$Ni is reproduced by the simple Glauber calculation assuming that the neutron-number dependence of charge radius is the same as that for Cu isotopes, charge radii of which are already known. In the region near the stability line, charge-changing cross section is considered to be fairly enhanced by the charged-particle evaporation effect, whereas this effect reduces for very neutron-rich nuclei [4]. With the present results, it is expected that this effect is negligible for Ni isotopes with A ${\geq}$ ${\sim}$72. So, in such a mass region, it is considered that the charge radius can be determined from ${\sigma}_{\rm{CC}}$ by a Glauber calculation without this evaporation effect.
In this presentation, we’ll report the matter radii and charge radii derived from the experimental cross sections using Glauber calculations. Also, in the region where the charge radii are known, from A = 58 to 70, we’ll discuss the neutron skin thickness of Ni isotopes, which is obtained by the present data combined with known charge radii. On the other hand, in the neutron-rich region with A ${\geq}$ 71, we’ll discuss the neutron skin thickness by combining present ${\sigma}_{\rm{I}}$ and ${\sigma}_{\rm{CC}}$ data.
References
[1] M. Centelles et al., Phys. Rev. Lett. 102 (2009) 122502.
[2] S. Malbrunot-Ettenauer et al., Phys. Rev. Lett. 128 (2022) 022502
[3] W. Horiuchi et al., Phys. Rev. C 93 (2016) 044611
[4] M. Tanaka et al., Phys. Rev. C 106 (2022) 014617
