A study of compressibility in nuclei far from the stability line

点击翻译按钮获取中文摘要

We have studied (α, α') reactions for proton- or neutron-rich unstable nuclei by using inverse kinematics in order to get a milestone for investigating E0 giant resonances and nuclear compressibility. A Liquid He target system was constructed where materials in a path of gamma rays from excited states were minimized and stability of the temperature were maintained through a 2-weeks experiment. The thickness of the target are selectable in a range of 100-250 mg/cm^2. By using 60-MeV secondary beams from the fragment separator RIPS in RIKEN accelerator facility, (a) ^<14>O+α and (b) ^<12>Be+α scatterings were measured. The detector system consisted of a hodoscope of plastic scintillators for charged particle detection and an array of 68 NaI(TI) scintillators for gamma rays. (a) The transition to 0^+, 1^-, 2^+ and 3^- excited states in ^<14>O were identified and the angular distributions of the differential cross sections were characterized by the transferred angular momenta. We also measured production cross sections of various fragments and found that production of carbon isotopes are much larger than a prediction of a semi-empirical rule. (b) We found an isomeric 0^+ state at 2.24 MeV just above the first excited state of the ^<12>Be, where its spin was determined by a gamma-gamma angular correlation pattern. Alpha inelastic scattering to the 2+ and 1- states were also measured, where the angular distributions are characterized by the transferred angular momenta. We newly found that the (α, t) and (α, ^3He) nucleon transfer reactions have significant cross sections, which gives a new spectroscopic tool for single particle states in unstable nuclei.