Fragment coincidence measurements for 58 Ni + 58 Ni collision at 29.3 MeV/u

Intermediate mass fragment (IMF) emission has been proved to be a powerful tool in studying the degree of equilibration of their sources in heavy ion induced reactions. At lower energies (< 10 MeV/u) the main source of IMF's in central collisions is represented by a fully equilibrated system produced in complete or incomplete fusion events. In this energy domain we studied the 58 Ni + 58 Ni system, showing that complete fusion produces IMF's with 3 ≤ Z ≤ 8. In order to study the energy evolution of the central collision mechanism and to check to which extent the IMF channel have sizeable cross sections, we have performed an experiment using a 58 Ni beam of 29.3 MeV/u delivered by the Superconducting Cyclotron of LNS-Catania. The measurements has been carried out using the experimental setup DRACULA Phase II. The twin position sensitive ionization chambers (ICs) used for fragment detection and identification spanned the angular range from 24 angle to 48 angle in laboratory system. For fragment detection and identification in the angular range from 0 angle to 24 angle two hybrid position-sensitive detectors (POSEIDONs) have been used. TOF measurements have been done using a four-section start PPAD placed in the target vicinity and the two PPAD which are in front of the ICs or the prompt signal plastic scintillator of the POSEIDONs as stop. A plot of the raw data used for on-line survey during the measurement, namely the specific energy loss ΔE1 of the products as a function of their velocity is give. The γ radiation was detected by 5 HPGe detectors mounted in the backward hemisphere in spherical geometry around the target. The position and energy calibration of the reaction products detected in ICs has been accomplished. The Galilei-invariant cross section (1/vtrans)σ(vlong, vtrans) for reaction products with atomic number Z = 6 - 9 is presented. The surface inside the thick full line is well filled by events showing the quality of the calibration. Putting gates on Z lines and correcting the coincident gamma ray energy for Doppler shift, gamma spectra for each IMF charge will be generated. The IMF characteristic discrete γ lines in the spectra will be used to deduce cross sections of bound excited states. In a first stage the analysis will concern the C, N and O isotopes, where the presence of excited levels spaced by a few MeV allows a good sensitivity in the effective temperature extraction. (authors)