Theoretical Study Of Prescission Particle Emission Based On Pathwise Analysis Method

There appear lots of new fundamental problems in nuclear physics, accompanying withthe quick development of heavy-ion physics and radioactive nuclear beam physics.Thenuclear dissipation (ND) draws various research works in low-energy nuclear reaction, andalso makes the deexcitation of hot nuclei more complicated, then it is a very important subjecthow to ascertain its intensity and deformation dependence. A best probe to study ND isprescission particle multiplicity, hence we investigate ND through carrying out preciseanalysis about the emission of prescission particle in the deexcitation process of hot nuclei.In the anterior two chapters of my thesis, we make a discription for the current researchstatus of ND, and detailed introdutions for two models, namely the combined dynamical andstatistical model (CDSM) and the modified CDSM (MCDSM), which simulate deexcitationprocess of hot nuclei.In the posterior two chapters, we draw a kind of new method to analyse the dynamicsproperties of deexcitation processm, i.e. pathwise analysis method. By means of the spirit ofnuclear mean field, we can take ND as a kind of friction force which frustrates motion of theBrownian particle alone deformation dimension, in addition the driving force for motion ofparticle stems from nuclear free energy. As such, the emission of prescission light particle isjudged by the competition between two forces alone deformation direction. Next, we discussthe deexcitation of hot nuclei200Pb and224Th using the new method, and the results show asfollows:(1) The amount of prescission neutron is relatively less with a stronger deformationdependence of level density parameter (DDLDP) as a result that the driving force isrelatively larger with such a DDLDP,and the position where the positive driving forcecomes forth is relatively closer the ground states.(2) The driving force with SPS ND is less than that of OBD ND, and it is most importantthat the intensity of the former is less than that of the latter in the first phase of nuclearfission. The two reasons result in the amount of prescission neutron is relatively lesswith SPS ND compared with OBD ND.(3) The emission of prescission neutron becomes weak after taken the action from nuclearcurvature energy and complessibility energy into account. The reason is that thereducation of driving force increases under the condition that height and deformationcoordinate of fission barrier change slightly.(4) The deformation coordinate of saddle point shifts forward calculated with MCDSMmodel as the number of mass of the hot nucleus increases, then the tendency which theemission of prescission neutron weakens is mainly controled by the emission in the firstphase of nuclear fission.(5) After taken the action from nuclear curvature energy and complessibility energy into account, the emission of prescission particles decreases in the first phase, and increasesin the second phase of fission. The descent of emission barrier of particle can boost upthe emission of prescission particles. The beforementioned twofold actions result in theprescission proton multiplicity barely changes, and the prescission alpha particlemultiplicity increases in the first phase. Besides that the emission of prescission chargedparticle increases under the action of two kinds of effect.The works in present thesis provides a kind of feasible analysis method to investigate theisospin effect of the emission of prescission particle.