Fissionlike exit channel in the 5.8 MeV/u84Kr on24Mg reaction

Abstract

Fissionlike (FL) phenomena for systems around mass 100 have been shown previously interpretable in terms of dynamical fission. This appears to be dependent on the entrance channel mass asymmetry. We have studied the fissionlike exit channel in the 84Kr+ 24Mg reaction at E(Kr)=5.8 MeV/u. This energy is just above the threshold of fission, so that a clear separation between the Deep Inelastic Component (DIC) and the FL one can be achieved. The bombarding energy corresponds to the same excitation energy in the composite system ~~ (E* = 101 MeV) as in the 32S (158 MeV) on 76Ge reaction we studied earlier and for which fusion-evaporation along with fission-like contributions were measured. The width of the FL distribution confirms the previously observed dependence with the mass asymmetry in the entrance channel which is consistent with the extra push model.The reaction 84Kr on 24Mg has been analysed in the framework of a systematic study of fissionlike (FL) deexcitation channel of the composite system l~ versus bombarding energy and the mass asymmetry in the entrance channel 1-1]. We have used an energy corresponding to the onset of fission, according to the rotating liquid drop model RLDM [2], where the inverted kinematics for all fully relaxed products are focused in a forward cone so that the different contributions can be analysed more easily. A double humped fully relaxed fragment distribution has been observed first in the 84Kr+Z7A1 reaction [31. The goal of the 84Kr+24Mg measurement is to look for such a two component distribution which has not been observed in the 32S+76Ge reaction. Another important aim is to measure the width of the FL component for which a strong dependence with the entrance channel mass asymmetry has been observed 1-1] in contradiction with the compound nucleus formation [2,4]. In this respect the present 84Kr In the study of the 32S+ 76Ge reaction [1] the fusion models have been shown to reproduce very well the fusion evaporation (FE) cross sections from nearly the coulomb barrier E B up to 2.3 EB: in particular the saturation predicted by the RLDM I-2] when the fission barrier B I drops under the neutron binding energy, is well followed. In an investigation of the influence of the entrance channel mass asymmetry leading to the isobar a~ Agarwal et al.[9] report a difference in the FE critical angular momenta lc FE measured for 16 0 + 92Mo FE (Icr = 59 _+ 3 h) and 52Cr+ 56Fe (/~FE=53 _+4 h). In the present case such a difference is not expected because the FE cross section measured for the 84Kr+ZTA1 reaction 1-10] (leading to the neighbouring CN rain) is very close to the value obtained for 32S+76Ge for nearly the same excitation energy in the CN. The experiences have been performed using a

The competition between fusion-fission and deeply inelastic reactions in the medium mass systems

“…See Figs. If the same point of view is taken, this observation is shown valid also to the other medium mass systems like S~Kr + 24Mg [26], 84Kr + 27A1 [24], 32S + 74Ge [11]. 11 for 37C1 n L 6~Ni.…”

A fast-fission component with small mass drift in the reaction84Kr+27Al atE lab=5.9 MeV/u

“…However, such decomposition has not been attempted yet. A similarly separable asymmetric fast-fission component was also found [3] in the system S4Kr +24Mg. It is interesting to note that the ratio between compound-nucleus and fast fission is very similar in both systems, despite the fact that their absolute cross sections differ by a factor of 5.…”

“…The availability of the evaporation residue cross section from an earlier experiment [1] and the possibility to obtain more data in the context of a systematical investigation [2,3] of fission reactions for systems with mass A~ll0 were reasons for choosing the reaction S~Kr + 27A1 at 5.9 MeV/u incident energy. In this paper we report results of cross section measurements for reaction products with Z--10 to around 40, covering the range from target-and pro-* Supported by BMFT Bonn jectile-like fragments to those from symmetric compound-nucleus fission.…”