Study On The Decay Properties Of Excited Nuclei

The highly excited nucleus with high excitation energy and high angular momentum is produced in the intermediate and high energy heavy ion collisions.It is significant to investigate the properties of the excited nucleus which is related to the understanding of nuclear equation of state,multifragmentation phenomenon,liquid gas transition,isospin effect and so on.The isospin-dependent quantum molecular dynamics model?IQMD?and a statistical model GEMINI are adopted to make comparative study of the decay properties of excited nucleus.The modified IQMD model could produce excited nuclei with different temperatures.The excited nuclei are decayed in the IQMD model and GEMINI model through free evolution and sequential decay,respectively.There are four main parts in this work:Fragmentation mechanism:The correlation between temperature and the mean multiplicity of intermediate mass fragments is given by analyzing the fragments distribution after the decay process.The proportions of three fragmentation phenomena,i.e.spallation,fission and multifragmentation are compared in different temperature regions using the event-by-event analysis method.Thus,the similarities and differences of the mechanisms between the two models could be learned.Liquid gas transition:The effective parameter?_effof the power-law is extracted by fitting the charge distribution of the fragments.Campi plots are also adopted to extract?₂ which represents the fluctuations in the fragments'size.?Campi plots are the distributions between the second moment of the fragments and the largest fragment?.It is found that the extracted?_{ef f}and?₂ by IQMD are more reasonable.The obtained possible critical region is T=8-10MeV.Slope temperature:Slope temperatures are extracted by fitting the kinetic energy distributions of the particles¹H,²H,³H,³He,⁴He.It is found that the slope temperatures are mass dependent for both models.The results of IQMD model are more reasonable.Comparison with experimental data:A series of excited nuclei are adopted to simulate the excited residual nuclei produced in the ¹²⁴Sn-^natSn experiment of projectile fragmentation.Those excited nuclei are decayed by the IQMD and GEMINI model,respectively.Then the<M_IMF>-Z_boundcorrelations are compared between the models and experimental data.It is found that the result of IQMD is consistent with experimental data.The trend of GEMINI is close to experimental data.Further analysis shows that GEMINI could well reproduce both the shape and width of the experimental isotopic distribution.The width of the isotopic distribution obtained by IQMD is too large.In conclusion,the decay properties of the excited nucleus are well reproduced within the IQMD model and it is shown that the IQMD model could be used alone in most cases.