Speaker
Description
The nuclear matter equation of state (EOS) is important not only for understanding the properties and structure of nuclei, but also astrophysical phenomena such as neutron star mergers and supernova explosions. In the field of experimental nuclear physics, efforts have been made to elucidate the EOS by determining the behaviour near saturation density and in symmetric matter by measuring various nuclear reactions or structure.
Recent studies suggest that high-precision, high-accuracy measurements of the isospin-dependent term of incompressibility ($K_\tau$) are important for determining the EOS. The value of $K_\tau$ can be directly derived from the isoscalar giant monopole resonance (ISGMR). Previous studies have obtained $K_\tau = -550 ± 100$ MeV from ISGMR measurements for Sn isotope. However, these measurements were limited to stable nuclei. Furthermore, there have been reports indicating the limitations of $K_\tau$ deriving using the droplet model, such as the splitting of the ISGMR spectrum in deformed nuclei and the so-called “softness,” where theoretical calculations do not match the experimental data. Therefore, it is necessary to measure ISGMR over a wide range of the nuclear chart and to investigate it in more detail, in order to elucidate the fundamental properties of nuclear matter, such as the incompressibility and the nuclear matter EOS.
To enable ISGMR measurements on unstable nuclei using inelastic scattering in inverse kinematics, an active target called CAT-M has been developed. The first experiments were conducted using stable Kr beams at the Heavy Ion Medical Accelerator in Chiba (HIMAC). As a result, we determined the centroid energy of ISGMR to be 17±1 MeV in $^{86}$Kr. In this presentation, we will report on the current status and results of these experiments, and discuss future plans for ISGMR measurements in unstable nuclei.
