Dissipation Properties Of Highly Excited Fissioning Nuclei

The nature and magnitude of nuclear dissipation are a hot topic in modern nuclear physics. A great number of experimental data provided in heavy-ion-induced fusion reaction, such as the multiplicities of prescission particles, fission and evaporation residue cross section, excitation energy at scission （Esc）, etc., have been employed to investigate nuclear dissipation properties in fission.In the framework of the stochastic Langevin model that accounts for light particle evaporation, we extract a friction value of （11-13）×10²1s^-1 by comparing theoretical predictions with measured neutron yields in fission of heavy compound nuclei 248^Fm,252^Fm,256^Fm and 251^Es. We find that deformation effects lowers the value of p needed to fit neutron data. Furthermore, calculations show that deformation significantly reduces the sensitivity of light charged particles （LCPs） on β and that excitation energy can substantially enhance the sensitive dependence of neutrons and LCPs on friction.An analysis for the data of excitation energy at scission （Exc） measured in 20^Ne+159^Tb and 20^Ne+169^Tm reactions reveals a postsaddle friction value of ～4×10²1s^-1 for light decaying systems. Moreover, we note that different from light particles, the Esc is not sensitive to deformation effects, indicating that it is a robust probe of nuclear dissipation.