25 research outputs found
Production of neutron-rich nuclei in fragmentation reactions of 132Sn projectiles at relativistic energies
The fragmentation of neutron-rich 132Sn nuclei produced in the fission of
238U projectiles at 950 MeV/u has been investigated at the FRagment Separator
(FRS) at GSI. This work represents the first investigation of fragmentation of
medium-mass radioactive projectiles with a large neutron excess. The measured
production cross sections of the residual nuclei are relevant for the possible
use of a two-stage reaction scheme (fission+fragmentation) for the production
of extremely neutron-rich medium-mass nuclei in future rare-ion-beam
facilities. Moreover, the new data will provide a better understanding of the
"memory" effect in fragmentation reactions.Comment: 5 pages, 3 figure
On the two-proton emission for Fe45 - a new type of radioactivity
In an experiment at the SISSI-LISE3 facility of GANIL, the decay of the
proton drip-line nucleus Fe45 has been studied after projectile fragmentation
of a Ni58 primary beam at 75 MeV/nucleon impinging on a natural nickel target.
Fragment-implantation events have been correlated with radioactive decay events
in a 16x16 pixel silicon strip detector on an event-by-event basis. The
decay-energy spectrum of Fe45 implants shows a distinct peak at
(1.06+/-0.04)MeV with a half-life of T1/2 = (4.7+3.4-1.4)ms. None of the events
in this peak is in coincidence with beta particles which were searched for in a
detector next to the implantation detector. For a longer correlation interval,
daughter decays of the two-proton daughter Cr43 can be observed after Fe45
implantation. The decay energy for Fe45 agrees nicely with several theoretical
predictions for two-proton emission. Barrier-penetration calculations slightly
favour a di-proton emission picture over an emission of two individual protons
and point thus to a He2 emission mode.Comment: 4 pages, 5 figures, sumitted to PR
Structure around the island of inversion with single-neutron knockout reactions at GANIL
CERN-Proceedings-2010-001 available at http://www.fluka.org/Varenna2009/procmat.htmInternational audienceThe nuclear structure of the 31Mg nucleus has been studied with the singleneutron knockout reaction. We report on the preliminary results of an experiment performed with the EXOGAM array coupled, for the first time, to the SPEG spectrometer at GANIL.We present a provisional result for the inclusive single-neutron knockout cross section of Ïinc= 90(5) mb. Preliminary exclusive cross sections for the measured bound states, including the ground state, are also presented. Finally, preliminary longitudinal momentum distributions for the ground state and first excited state are also shown. These results are compared to Monte Carlo Shell-Model calculations in the sd-pf region
Structure around the island of inversion with single-neutron knockout reactions at GANIL
The nuclear structure of the 31Mg nucleus has been studied with the singleneutron knockout reaction. We report on the preliminary results of an experiment performed with the EXOGAM array coupled, for the first time, to the SPEG spectrometer at GANIL.We present a provisional result for the inclusive single-neutron knockout cross section of Ïinc= 90(5) mb. Preliminary exclusive cross sections for the measured bound states, including the ground state, are also presented. Finally, preliminary longitudinal momentum distributions for the ground state and first excited state are also shown. These results are compared to Monte Carlo Shell-Model calculations in the sd-pf region
Neutron-rich fragments produced by in-flight fission of U-238
The production cross sections of neutron-rich fission residues in reactions induced by U-238 projectiles at 950A MeV impinging on Pb and Be targets are investigated at the Fragment Separator at GSI. These two targets allow us to investigate fission processes induced by two reaction mechanisms, Coulomb and nuclear excitations, and to study the role of these mechanisms in the neutron excess of the final fragments.Peer reviewe
Systematic reduction of the proton-removal cross section in neutron-rich medium-mass nuclei
Single-neutron and single-proton removal cross sections have been measured for medium-mass neutron-rich nuclei around Z=50 and energies around 1000A MeV using the FRagment Separator (FRS) at GSI. The measured cross sections confirm the relative low values of the proton-removal cross sections, observed since a long time ago and not yet understood. Model calculations considering the knock-out process together with initial- and final-state interactions describe the measured neutron-removal cross sections. Proton-removal cross sections are, however, significantly over-predicted by the same calculations. The observed difference can be explained to a large extent by the knock-out of short-range correlated nucleons from dominant neutron-proton pairs in neutron-rich nuclei. © 2020 The Author(s)Peer reviewe
Re-examining the transition into the N=20 island of inversion: structure of 30Mg
Intermediate energy single-neutron removal from Mg has been employed
to investigate the transition into the N=20 island of inversion. Levels up to
5~MeV excitation energy in Mg were populated and spin-parity assignments
were inferred from the corresponding longitudinal momentum distributions and
-ray decay scheme. Comparison with eikonal-model calculations also
permitted spectroscopic factors to be deduced. Surprisingly, the 0
level in Mg was found to have a strength much weaker than expected in
the conventional picture of a predominantly intruder configuration
having a large overlap with the deformed Mg ground state. In addition,
negative parity levels were identified for the first time in Mg, one of
which is located at low excitation energy. The results are discussed in the
light of shell-model calculations employing two newly developed approaches with
markedly different descriptions of the structure of Mg. It is concluded
that the cross-shell effects in the region of the island of inversion at Z=12
are considerably more complex than previously thought and that
configurations play a major role in the structure of Mg.Comment: Physics Letters B, Volume 779, 10 April 2018, Pages 124-12
How sharp is the transition into the N=20 island of inversion for the Mg isotopes ?
International audienceThe N=20 island of inversion is an excellent playground for testing shell model calculations. The Mg chain is a region of shell evolution still far from being well understood. In this paper we present preliminary results of a single-neutron knockout experiment from 31Mg performed at GANIL to study the structure of 31Mg and of the core 30Mg. The level scheme and longitudinal momentum distributions were mesured and spectroscopic factors were deduced. Negative parity states arise at low energy and the spectroscopic factor for the isomeric in 30Mg was determined to be smaller than foreseen in the standard picture. The preliminary experimental results are compared to state-of the art shell model calculations revealing opposed interpretations