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N u c l e a r P h y s i c s :
Main directions of scientific activity (continuation - page3)
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").
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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Exotic Nuclei.