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Register a new userIsospin Diffusion and Equilibration for Sn+Sn collisions at E/A=35 MeV
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Equilibration and equilibration rates have been measured by colliding Sn nuclei with different isospin asymmetries at beam energies of E/A=35 MeV. Using the yields of mirror nuclei of 7Li and 7Be, we have studied the diffusion of isospin asymmetry by combining data from asymmetric 112Sn+124Sn and 124Sn+112Sn collisions with that from symmetric 112Sn+112Sn and 124Sn+124Sn collisions. We use these measurements to probe isospin equilibration in central collisions where nucleon-nucleon collisions are strongly blocked by the Pauli exclusion principal. The results are consistent with transport theoretical calculations that predict a degree of transparency in these collisions, but inconsistent with the emission of intermediate mass fragments by a single chemically equilibrated source. Comparisons with ImQMD calculations are consistent with results obtained at higher incident energies that provide constraints on the density dependence of the symmetry energy.
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Experimental results concerning the dynamical fission of quasiprojectiles in semiperipheral collisions for the system 80 Kr+ 48 Ca at 35 MeV/nucleon are presented. Data have been collected with four blocks of the FAZIA setup in the first physics experiment of the FAZIA Collaboration. The degree of isospin equilibration between the two fission fragments and its dependence on their charge asymmetry is investigated. The data are compared with the results of the AMD model coupled to GEMINI as an afterburner, in order to get hints about the timescale of the process.
We present a new experimental method to correlate the isotopic composition of intermediate mass fragments (IMF) emitted at mid-rapidity in semi-peripheral collisions with the emission timescale: IMFs emitted in the early stage of the reaction show larger values of $<$N/Z$>$ isospin asymmetry, stronger angular anisotropies and reduced odd-even staggering effects in neutron to proton ratio $<$N/Z$>$ distributions than those produced in sequential statistical emission. All these effects support the concept of isospin migration, that is sensitive to the density gradient between participant and quasi-spectator nuclear matter, in the so called neck fragmentation mechanism. By comparing the data to a Stochastic Mean Field (SMF) simulation we show that this method gives valuable constraints on the symmetry energy term of nuclear equation of state at subsaturation densities. An indication emerges for a linear density dependence of the symmetry energy.
Single-particle kinetic energy spectra and two-particle small angle correlations of protons ($p$), deuterons ($d$) and tritons ($t$) have been measured simultaneously in 61A MeV $^{36}$Ar + $^{27}$Al, $^{112}$Sn and $^{124}$Sn collisions. Characteristics of the emission sources have been derived from a ``source identification plot ($beta_{source}$--$E_{CM}$ plot), constructed from the single-particle invariant spectra, and compared to the complementary results from two-particle correlation functions. Furthermore, the source identification plot has been used to determine the conditions when the coalescence mechanism can be applied for composite particles. In our data, this is the case only for the Ar + Al reaction, where $p$, $d$ and $t$ are found to originate from a common source of emission (from the overlap region between target and projectile). In this case, the coalescence model parameter, $tilde{p}_0$ -- the radius of the complex particle emission source in momentum space, has been analyzed.
Collisions of Xe+Sn at beam energies of $E/A$ = 8 to 29 $MeV$ and leading to fusion-like heavy residues are studied using the $4pi$ INDRA multidetector. The fusion cross section was measured and shows a maximum at $E/A$ = 18-20 $MeV$. A decomposition into four exit-channels consisting of the number of heavy fragments produced in central collisions has been made. Their relative yields are measured as a function of the incident beam energy. The energy spectra of light charged particles (LCP) in coincidence with the fragments of each exit-channel have been analyzed. They reveal that a composite system is formed, it is highly excited and first decays by emitting light particles and then may breakup into 2- or many- fragments or survives as an evaporative residue. A quantitative estimation of this primary emission is given and compared to the secondary decay of the fragments. These analyses indicate that most of the evaporative LCP precede not only fission but also breakup into several fragments.
Multifragment disintegrations, measured for central Au + Au collisions at E/A = 35 MeV, are analyzed with the Statistical Multifragmentation Model. Charge distributions, mean fragment energies, and two-fragment correlation functions are well reproduced by the statistical breakup of a large, diluted and thermalized system slightly above the multifragmentation threshold.
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