Study Of The Two-Dimensional Scission-point Model And Fission TPC Detector Based On The Neutron Induced Actinide Nuclear Fission

As one of the most important decay modes,nuclear fission plays an essential role in developing low and intermediate energy nuclear physics experiments and theories.At the same time,it also contains abundant physical information,such as shell struc-ture,spin,and the asymmetry of mass and charge,etc.,and it will also lead to the termination of r-process in the evolution of celestial bodies.However,up to now,due to the complex quantum effects and the limitations of experimental technology,there are still a series of opening questions in theory and experiment.Current theories gen-erally believe that multiple modes in the fission process correspond to various valleys from saddle point to the scission point on the potential energy surface of parent nucle-us,leading to a specific shape of the parent nucleus different valleys on the potential energy surface.However,in experiments,most traditional studies mainly focused on describing a single observable measurement,such as the mass distribution,charge dis-tribution,total kinetic energy,or cross-section of the fission fragments.Moreover,a large number of experimental results have been accumulated.However,in the theo-retical analysis,the single observable description frequently requires integrating other variables within the range of possible values.Therefore,it is insensitive to the lo-cal structure for the potential energy surface of the parent nucleus.Different fission paths cannot be distinguished as well.Naturally,the correlation between the different observable characteristics is of considerable significance to further extract fission infor-mation.In recent years,with the expansion of the neutron beam energy region and the development of association technology,there are large achievements in the association measurement of neutron-induced actinide elements nuclear fission.That enables us to have a deeper understanding of the relationship between multi-parameters of fission fragments and better explore the reaction mechanism of nuclear fission.Given the idea mentioned above,theoretically,the interaction potential energy of two fragments that are quite close to each other is analyzed using the concept of the di-nuclear system(DNS)in super-heavy nuclear cold fusion synthesis.According to the lowest energy principle,the tip-to-tip orientation is always taken during the nu-clear system's evolution.Compared to other orientations,it tends to have a relatively high internal fusion barrier and a lower external coulomb barrier evolving along the r-direction,which will increase the probability of fission.By considering the tip-to-tip orientation at the scission point of the fission process.The variation of the drive potential with the fission fragment asymmetry?is investigated,reflecting the fission fragment yield distribution.And then,the driving potential of DNS is considered into the two-dimensional scission-point model(TDSPM)for calculation.In the model,the ground state deformation of the nucleus and the damping effect of the shell are also taken into account.Finally,we investigate the mass,charge,and kinetic-energy distri-bution of fission fragments at excitation energy(0-20)Me V using the TDSPM.It shows that the fission fragment distributions can be reproduced very well,including the recent experimental results on the isotone chain.Agreement with theoretical results is perfect for the peak position,width,and height of fission yields.Especially for the charge dis-tributions,the odd-even effect of nuclei is well explained.That indicates the simplified method will be useful for realizing the multi-parameter global measurements of fission products.In the experiment,we are building a time projection chamber detector based on GEM technology.This thesis completes the design and construction of the low-pressure fission TPC.The detector mainly consists of four parts:low-pressure control system,fission TPC detection system based on GEM,the auxiliary measuring system of the delayed?,and back-end electronics readout system.The detector adopts flow-gas pres-sure automatic regulation system,and through simulation,the whole detector needs to maintain the working pressure at about 25 k Pa?42 k Pa.The readout system of the detector is composed of 13APV-25 integrated preamplifier chips controlled by a piece of data acquisition master plate,and a total of 1634 channels of electronics readout is realized.The system can continuously sample a single signal for 30 cycles;each cycle has 25 ns,50 ns in total.As the core component of the whole fission TPC detector,the fission TPC detection system based on GEM technology is mainly composed of two GEM,a drift pole,and a PCB readout board,which is used to complete the generation,ionization,electron multiplication and collection of fission fragments.In addition,ex-cept for the delayed?auxiliary measurement system,the machining and construction of the main structure of the other detectors have been completed.And the performance of the detectors has been tested by using the X-ray source of⁵⁵Fe at constant pressure.At low pressure,the performance of the whole detection system was tested by using the X-ray source of⁵⁵Fe and the?source of the smoke alarm.The test results show that the whole detector has stable performance and is expected to measure single fission fragment information in the future accurately.