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, 11Li, 11Be, 12Be, 14Be and 8Be have been measured. The results obtained
on the nuclear matter density distributions represent a clear signature of nucleon halos
(skins) in 6He, 8He, 11Li, 12Be and 14Be. 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
"EXPERIMENTAL STUDY OF THE NUCLEAR SPATIAL STRUCTURE OF NEUTRON-RICH He AND Li ISOTOPES" in PNPI HEPD Report
MAIN SCIENTIFIC ACTIVITIES of High Energy Physics Division in 2002-2006" - page 176).
IRIS (Investigation of Radioactive Isotopes on Synchrocyclotron) is the first in Russia ISOL (Isotope Separator On-Line)
installation for studies of nuclei far from the stability line. Its operation was started in 1975. The main part of IRIS
is the mass-separator on-line with the 1 GeV proton beam of the PNPI synchrocyclotron. Nuclei far from stability are
produced by interaction of 1 GeV protons with a target. The nuclides obtained in reactions with high energy protons are
released from the target material at the high temperature, ionized in the ion-source and subsequently after mass-separation
as a single charge ion beams directed through the vacuum ion-guides, which are equipped by electrostatic elements to be
implanted into the collectors of experimental setups. The obtained by this way the radioactive sources can be studied
using the conventional alfa-, beta-, gama- detectors as well as some other systems of registration.
One of the most efficient methods to study nuclei far from the beta stability line appeared to be the method of resonant laser photoionization technique. For the first time this method has been used for the study of properties of the ground and isomeric states of nuclei at the IRIS facility. Later at the IRIS facility as well the basically new modification of this method (mentioned above) has been developed and used (for the first time and it was the resonant photoionization) inside the laser ion source . By means of the method of the laser spectroscopy the isotopic changes of mean square radii and electromagnetic moments of more than 100 neutron-deficient nuclei in the rare earth elements region.
In experiments at IRIS facility masses of more than 100 unstable nuclei have been derived from the experimental values of beta decay energies of nuclei under investigation. Using the obtained experimental data on the beta+ strength functions, the resonant structure of them has been demonstrated for the first time.
Some of the important activity directions of the Laboratory for study of short lived nuclei are presented below: