HEPD-Activities/Nuclear Physics

Exotic Nuclei.

According to a proposal from PNPI, exotic halo nuclei, such as ⁶He, ⁸He,¹¹Li, are studied at GSI by the method of proton elastic scattering in inverse kinematics. Secondary ion beams from the fragment separator FRS at the GSI heavy-ion synchrotron SIS are scattered in the hydrogen-filled ionization chamber IKAR which serves simultaneously as a gas target and a detector of recoil protons. The scattering angle of the projectile is also measured by multiple wire proportional chambers. In this way, the differential cross sections for proton elastic scattering from exotic nuclei are measured at small momentum transfers. The measured cross sections allow one to obtain information on the nuclear matter distributions. By present, the differential cross sections for proton scattering on ⁶He, ⁸He, ⁶Li, ⁸Li, ⁹Li and ¹¹Li have been measured. The results obtained on the nuclear matter density distributions represent a clear signature of nucleon halos (skins) in ⁶He, ⁸He and ¹¹Li. Measurements of proton scattering on ⁸B and¹⁴Be are planned. An experiment for measuring cross sections at larger momentum transfers is also under way.
(For more detail review see article "Study of Nuclear Matter Distribution in Neutron-Rich He and Li Isotopes" in PNPI HEPD Report "Main Scientific Activities 1997-2001").

Investigation of nuclei far from stability at IRIS.

IRIS (Investigation of Radioactive Isotopes on Synchrocyclotron) is the first in Russia ISOL (Isotope Separator On-Line) installation for studies of nuclei far from stability. It started its operation in 1975. The main part of IRIS is a mass-separator working on-line with the 1 GeV proton beam of the PNPI synchrocyclotron. Nuclei far from stability are formed as a result of interaction of 1 GeV protons with a target. The atoms of the produced nuclei are thermally released from the target, ionized in the ion-source and are mass-separated. Then they are studied with conventional spectroscopy detectors or by using some dedicated techniques such as laser spectroscopy. It could be mentioned that the resonant ionization spectroscopy technique, which has been proved very efficient for studies of nuclei far from stability, was proposed and launched with this purpose for the first time at IRIS, PNPI. Masses of more than 100 unstable nuclei were determined at IRIS. Charge radii of more than 100 nuclei were also measured. The resonant structure of the b⁺ strength functions was demonstrated for the first time. Some important directions of the investigation carried out at IRIS are presented below.

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