Central collisions in theO16+12

Abstract

Central collisions of 0 on a C target have been studied at 32.5 MeV/A. An analysis in terms of incomplete fusion followed by statistical decay is presented and the main channels for the incomplete fusion are extracted for this reaction. A detailed study of the specific channel, GHe+2H, shows a good agreement with a statistical decay of the Mg parent nucleus while a multifragmentation model predicts a larger sphericity for these events. PACS number(s): 25.70.Mn I. INTR, ODUCTION Breakup studies of light nuclei such as 0 and Ne in peripheral reactions [1] have shown consistency witha statistical decay process. In these inelastic collisions the system undergoes a relatively gentle reaction, which could be the reason for the apparent equilibration decay. In order to search for nonequilibrium phenomena, we studied central collisions where hotter nuclei are formed. We chose a relatively light system 0 beam at 32.5MeV/nucleon of incident energy on a C target and selected central collisions by requiring a large multiplicity of fragments in the multielement detector used to observe the reaction.After a description of the experimental apparatus, we present an analysis of the center of mass velocity to de-termine the main composite nuclei formed through incomplete fusion. We then examine in detail a channel in which a large number of particles and large total charge is detected, the 5He+2H channel. A sphericity and coplanarity of the events are determined and compared with simulations.tons up to 100 MeV. In the position-sensitive detectors the E element was 2.5 cm thick. The thresholds for particle identification ranged from 8 MeV for protons to 10 MeV per nucleon for Be, B, and C.For a TP detector three values were recorded for every detected particle: a "short gate" value (Sg), which was the fast component of the output signal integrated in a 40 ns gate, a "long gate" value (l:g), which was the integration of the total signal in a 2 ps gate, and a time signal. The short gate corresponded approximately to the energy deposited in the LE element and the long gate approximately to the total energy. For a positionsensitive detector, Ave values were recorded: two Sg values and two Zg values, one for each end of the detector, TP Phoswich Detectors II. EXPEH.IMENT Beam Exit '--:=!SR@ =SR Saesm essay & iThe experiment was performed at the LBL 88-inch Cyclotron and the detection system (Fig. 1) consisted of an array of 48 truncated pyramidal (TP) plastic phoswich detectors covering the forward angles from 2. 5' to 17. 5' [2] and 10 position-sensitive plastic phoswich detectors [3], covering larger angles up to 78' in the horizontal direction and 56 in the vertical direction. All plastic detectors were of the LE-E type and had a 0.4 mm thick fast scintillator (BC-404) for the AE element and a slow scintillator (NE-115) for the E element. The E element in a TP detector was 10.2 cm thick and could stop proSlice Phoswich Detectors FIG. 1. Plastic phoswich detector array for light charged particles. The slices are positioned symmetrical...