Speaker
Teresa Kurtukian-Nieto
(Universidad de Santiago de Compostela,Spain)
Description
The complete understanding of the r-process still remains a challenge not only
because of the identification of the possible astrophysical sites but also because
of the interpretation of the observed abundances. With respect to this latter
point, one of the main problems we have to overcome to fully understand the
observed r-process abundances is the lack of information on the nuclei
participating in this process, in particular for the heaviest ones. The main reason
for this is that the heavy nuclei involved in the r-process are so neutron-rich
that until now they have been far from any experimental access.
During the last years promising results have been obtained investigating the
properties of medium-mass neutron-rich nuclei close to the waiting point A=130 [1]
while the waiting point around A=195 remains a completely unexplored territory.
Nevertheless, the possibility to accelerate heavy ions at relativistic energies has
allowed the investigation of reactions mechanisms leading to the production of
heavy neutron-rich nuclei such as cold-fragmentation reactions [2].
In this work we report on an experiment performed with the FRS at GSI to explore
the production of heavy neutron-rich nuclei close to the neutron shell N=126 and
to measure their beta half-lives. We used cold-fragmentation reactions induced by a
208Pb beam at 1 AGeV impinging a Be target to produce heavy neutron-rich nuclei
south of lead. The isotopic identification of the projectile residues was achieved
by determining both the atomic number and the mass-over-charge ratio of each
nucleus by measuring their magnetic rigidity, time-of-flight and energy loss. The
identified nuclei were implanted in an active catcher made of four 5x5 cm2 Double-
Side Silicon Strip Detectors 1 mm thick. The position and time correlations between
the implanted nuclei and the subsequent beta decay allowed the determination of the
beta half-lives.
In this measurement we were able to identify for the first time around 30 new
neutron-rich nuclei approaching the neutron shell N=126. In addition, the half-life
of some of them has been determined. These half-lives have been compared with model
calculations [3,4] which in general do not reproduce the measured values. This work
opens new perspectives for further detailed spectroscopic investigations coupling
with gammas that will allow us better understand the structure and decay properties
of the A=195 waiting point nuclei.
[1] Dillmann I., Kratz K.-L., et at Phys. Rev. Lett. 91, 162503 (2003)
[2] Benlliure J., et al. Nucl. Phys. A 660, 87, (1999)
[3] Tachibana T. et al. Proc. Int. Conf. on Exotic Nuclei and Masses, A 660, Arles,
763 (1995)
[4] P. Möller et al. Atomic Data and Nuclear Data Tables, 66, 131 (1997)
Authors
Jose Benlliure
(Universidad de Santiago de Compostela,Spain)
Karl-Heinz Schmidt
(GSI Darmstadt,Germany)
Teresa Kurtukian-Nieto
(Universidad de Santiago de Compostela,Spain)
Co-authors
B. Blank
(CENBG Bordeaux-Gradignan, France)
B. Jurado
(GSI Darmstadt,Germany)
D. Cortina-Gil
(Universidad de Santiago de Compostela,Spain)
D. Henzlova
(GSI Darmstadt,Germany)
E. Casarejos
(Universidad de Santiago de Compostela,Spain)
F. Becker
(GSI Darmstadt,Germany)
F. Rejmund
(Institute de Physique Nucléaire, Orsay, France)
J. Giovinazzo
(CENBG Bordeaux-Gradignan, France)
J. Pereira
(Universidad de Santiago de Compostela,Spain)
L. Audouin
(Institute de Physique Nucléaire, Orsay, France)
M. Fernandez-Ordoñez
(Universidad de Santiago de Compostela,Spain)
O. Yordanov
(GSI Darmstadt,Germany)
