The Study Of The Correlation Effects In The Low-energy Positron Annihilation Processes In Atoms And Molecules

After decades of development,the research of positron annihilation has made great achievements and been widely used in many fields of science and technology.However,the existing theoretical methods yield much wider gamma ray spectra than the experimental ones.Although the effect of correlation on the annihilation process has been considered,it only corrects the gamma-ray spectra of some atoms and molecules,not all of the annihilation gamma-ray spectra from theoretical heights.This can be attributed to the existing theoretical methods are not systematic,using some approximate methods to simulate the positron behavior,and not using the accurate positron wave function to calculate the gamma-ray spectrum.In this paper,the gamma-ray spectra of several molecular systems are calculated by using low-energy positron plane wave approximation,and the functions of various electrons in the process of annihilation are analyzed.It is shown that the accurate positron wave function and the positron-electron correlation effect should be considered in the process of annihilation.The positron wave function and electron wave function are solved simultaneously by means of quantum mechanics by constructing a completely self-consistent field approximation method.The zero-order approximate equation and the first-order approximate equation containing exact electron and positron wave function are obtained.The gamma ray spectra of helium and neon as well as hydrogen and methane are calculated.Comparing the data with the data under the low-energy positron plane wave approximation,it is found that the zero-order approximation of many-body theory has about 20% correction effect on the low-energy positron plane wave approximation,while the first-order approximation has almost no correction effect on the zero-order approximation.It is proved that the precise positron wave function and the correlation effect between positrons and electrons play an important role in the process of low energy positron annihilation.The results of this paper hope to provide a reference for the process of the annihilation of positrons and electrons in macromolecules and promote the theoretical development of positron annihilation.Although the theoretical calculated value in thispaper is in good agreement with the experimental data,the difference between the theoretical value and the experimental value is not completely solved,but the gap is narrowed.The wave function and annihilation mechanism of incident positrons need to be described more accurately in future work.