Isotope correlations as a probe for freeze-out characterization: central 124Sn+64Ni, 112Sn+58Ni collisions

124Sn+64Ni and 112Sn+58Ni reactions at 35 AMeV incident energy were studied with the forward part of CHIMERA multi-detector. The most central collisions were selected by means of a multidimensional analysis. The characteristics of the source formed in the central collisions, as size, temperature and volume, were inspected. The measured isotopes of light fragments (3 <= Z <=8) were used to examine isotope yield ratios that provide information on the free neutron to proton densities.Comment: 4 pages, Contribution to 8th International Conference on Nucleus-Nucleus Collisions, Moscow 200

Properties of very hot nuclei formed in Zn-64+Ti-nat collisions at intermediate energies

Formation and decay of hot nuclei have been studied in Zn-64 + Ti-nat collisions between 35 and 79 MeV/nucleon. The mass and excitation energy of excited quasiprojectiles are reconstructed from the kinematical characteristics of their decay products. In central collisions, excitation energies larger than 10 MeV/nucleon are reached. Comparisons with theoretical predictions indicate that a fraction of the excitation energy is associated with an isotropic radial flow

Gamma-ray Multiplicity Measurements for the Determination of the Initial Angular-momentum Ranges in Normal and Fast Fission Processes

Gamma-ray multiplicities (first and second moments) have been measured, in the 220 MeV 20Ne + natRe and 315 MeV 40Ar+165Ho reactions, as a function of fission fragment masses and centre-of-mass total kinetic energies. The two reactions lead to the same fusion nucleus, 205At, at the same excitation energy (167 MeV). The experimental critical angular momentum for the fission process in the Ne + Re system (91 ± 3) ℏ is close to lBf=0 (~80ℏ) while in the Ar + Ho reaction this critical angular momentum (136 ± 4) ℏ is much larger than the lBf=0 value, favoring the occurrence of the fast fission process. The observed widths of the fission fragment mass distribution: (42 ± 2) u in the Ne + Re system and (56 ± 4) u in the Ar + Ho reaction strengthen this hypothesis. For both compound nucleus fission and fast fission components in Ar + Ho, the total spin values obtained in absolute magnitude and in their dependence on the mass asymmetry are well described by assuming rigid rotation of the fissioning complex and statistical excitation of some collective rotational modes such as "Bending" and "Wriggling" according to the Schmitt-Pacheco model. These modes, however, are not all fully excited, their degrees of excitation are approximately the same for both fission components. From theoretical estimates of equilibration times, one anticipates the "Tilting" mode to be by far the last to be excited, and from its non-excitation in the present data together with the excitation of bending and wriggling, a time interval of about 10-21 s to 2 × 10-20 s can be derived for the reaction time of both normal fission and fast fission. The γ-ray multiplicity as a function of the c.m. total kinetic energy decreases in the Ne + Re system, while it increases in the Ar + Ho system even for symmetric splitting, which indicates experimentally for the first time that fast fission populates the whole mass range. This difference between the two reactions is in agreement with the normal-fission-fast-fission distinction in angular momentum space. © 1990.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Directed collective flow and azimuthal distributions in Ar-36+Al-27 collisions from 55 to 95 MeV/u

A 4 pi charged particle detector array with a low velocity threshold has been used to detect the products from reactions induced by Ar-36 on Al-27 at energies ranging from 55 to 95 MeV/u. Well characterized events were selected and sorted as a function of the impact parameter. Two methods were used for sorting these events with respect to their impact parameters and three methods were compared to determine the reaction plane. The transverse momentum analysis has been found to be the best method to extract the direction of the reaction plane for this system and for the experimental set-up used here. The energy of vanishing flow for central collisions has been found to be around 90-95 MeV/u. The azimuthal distributions of mid-rapidity particles exhibit a preferential in-plane emission and no squeeze-out effect

用次级束流对硅望远镜的时间和能量定标

利用95MeV/u的~(16)O束产生的次级束流对半导体硅探测器进行了时间和能量定标。实验结果表明,由于次级束流提供的次级粒子种类多,飞行距离长,因此,能给探测器带来非常精确的定标