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LoI_SP2_Ph2 40: The role of the Isospin in the formation and decay of excited nuclei

Letter of intent for the SPIRAL2 Phase II - Day One

by FAZIA Collaboration - published on , updated on


Beams of Kr isotopes will be accelerated by the Spiral2 facility under 10 AMeV.
The idea of the present proposal is to employ these isotopes, together with some stable beams, to investigate several aspects of the reaction mechanisms which are expected to depend on the N/Z ratio. In particular we will focus on the interplay of the dynamics and the sequential decay of the excited fragments produced in dissipative collisions.
In this energy regime, not much above the Coulomb barrier, reactions proceed via nucleon exchanges which are mainly ruled by the mean field. The main exit channels are fusion (complete or incomplete)
and deep-inelastic interaction, the latter dominating for heavier systems. The details of the mean field, the role of neutron-rich surfaces and their fluctuations during the formation of final products are poorly known especially in systems characterized by exotic isospin values where very selective data are scarce so far.
The thresholds and the limitations imposed by the detectors are severe at low energies; our collaboration intends to pursue this investigation at GANIL by means of the FAZIA array, a new modular apparatus where the mass and charge identi-cation capabilities of silicon and CsI detectors are pushed to their limits thanks to detector improvement and extensive use digital electronics. The proposed activity is strongly connected to other initiatives of the FAZIA collaboration, which mainly operates at GANIL and at the INFN Laboratori in Legnaro and Catania.


This proposal aims at studying the influence of isospin in the formation and decay of excited states of nuclei formed in heavy-ion reactions at energies slightly above the Coulomb barrier and
for N/Z ratios that vary between about 1.1 and 1.6. Beams of krypton isotopes from SPIRAL2, namely 80Kr and 94Kr, at around 10 A·MeV or slightly below will be used.
At these energies, mean-field effects are dominant and heavier nuclei are formed by fusion and/or deep-inelastic collisions (DIC). Evolution of the formed system and its N/Z equilibration are still poorly understood. Investigation of isospin-sensitive observables in fusion (+fission) and DIC is very important and is connected to the equation of state of nuclear matter through the link of isospin drift and diffusion to density dependence of the symmetry energy in asymmetric nuclear matter.
The proponents intend to use a whole arsenal of detection equipment such as the technically very advanced detector array FAZIA with excellent mass and charge identification capabilities
together with low detection thresholds.
This will be coupled with INDRA to extend the detection
efficiency, with VAMOS to allow tagging with identified evaporation residues and possibly with neutron detectors to characterise the reactions as fully as possible.

The physics addressed with this LoI is quite interesting. It requires strong support from theory and the collaboration has managed to successfully engage theoretical groups in this research programme. It is important that the theory support is given at an early stage to help the collaboration identify the most important observables to look for experimentally. With the help of this theoretical support it would be useful if the collaboration performs simulations showing what
detection scenarios of interesting physics one can expect with the different detector combinations proposed.

[1from the Minutes of the meeting of SPIRAL2 Scientific Advisory Committee (SAC) held in
Caen on 26-28 January 2011