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Selected results from the RISING Stopped Beam Campaign

L. Caceres (GSI-Darmstadt)

When 2008-09-26
from 11:00 am à 12:00 pm
Where salle des séminaires du GANIL
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The main goal of RISING (Rare Isotope Spectroscopy INvestigation at GSI) is to study
exotic nuclei both in the proton and in the neutron rich side of the nuclidic chart. The
presented experiments were part of the RISING stopped-beam campaign. As a common
characteristic, all the nuclei of interest were produced by fragmentation and/or induced
fission reactions. The reaction products were separated by means of the B-E-B method
in a event-by-event basis in the FRagment Separator spectrometer (FRS) [1]. The isomeric
states populated in the reaction which survived the flight-path through the FRS were
implanted in a passive stopper positioned in the last focal plane of the FRS. A high
efficiency and high granularity Ge-array placed in close geometry surrounding the stopper
was used to measure the
-rays from the isomeric decays. The Ge-array consists of 15
cluster detectors from the former EUROBALL [2] spectrometer. In order to constract
the level scheme a combined information from

 coincidence and half-life analysis was
performed. A tentative spin and parity assignment of the excited states has been deduced
based on the transition probabilities and systematics.
On the neutron rich nuclei side of the nuclidic chart, the experiments focused on the
decay of isomeric states in the even-even 126Cd [3], 128Cd [4], 130Cd [5] isotopes and 131In
[6]. Large Scale Shell Model (LSSM) calculations which considered the size of N = 82
shell gap as it is known in 132Sn were performed. The remarkable agreement between the
experimental level scheme of 130Cd and 131In and the calculations lead to the conclusion
that no evidence for shell quenching at N = 82 and Z = 48 is observed. In addition, a
flattening of the 2+ excitation energies in the Cd isotopes [7] up to N = 80 compared
to the neighboring isotonic chains could be explained by the  interaction with strong
wave function overlap due to the same particle (hole) character for protons and neutrons.
The experimental results will be presented and discussed in terms of the systematics and
LSSM calculations.
On the very neutron deficient side of the nuclidic chart the study of low lying structures
in the N=Z 82Nb [8] and 86Tc [9] will be reported. The results are compared to Projected
Shell Model calculations suggesting that the observed isomeric state in 82Nb could be
interpreted as an K isomer. In addition the results shed light to the shape evolution from
56Ni to 100Sn and favors the T=1 isovector coupling in the heavy N=Z nuclei.


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