Research On The Online Monitoring Method Of Intensity Of Positron Beam Based On²²Na Slow Positron Beam Device

The study of intensity of positron beam based on 22Na slow positron beam device is of great significance in many scientific research and technology applications.For example,it can promote the experimental research of positron-atomic ionization or scattering,help reveal the mechanism of interaction between positrons and atoms;It also can help to obtain accurate positronium conversion,and then better study quantum electrodynamics;The intensity of positron beam is also indispensable basic data in aspects such as the upgrade of the efficient moderator in the slow positron beam device,the detection of electromagnetic field performance,and the improvement of the experimental efficiency of the slow positron annihilation technology by predicting the energy spectrum collection time.The intensity of positron beam produced by the 22Na slow positron beam device is generally weak(usually?106e+/s),and the traditional method of Faraday tube for obtaining beam intensity online is no longer applicable.The methods for obtaining beam intensity in published references at home and abroad can be roughly divided into two types:offline methods and online methods.Given the complexity of the device and the instability of the moderator and the transmission magnetic field,the offline method is obviously not accurate enough.However,the existing online methods have shortcomings.Based on the status quo,the following work has been carried out in this paper:(1)A new method for online monitoring of intensity of positron beam has been developed,which uses HPGe to record the 511 keV photons generated by the slow positron collision target annihilation,taking into account Monte carlo realistic simulation of electromagnetic fields in the target chamber.(2)Based on the annihilation photon data generated by positron collisions with different pure thick targets,the new method developed in this paper and the existing online method are compared and analyzed.(3)The real-time changes of positron beam intensity when positrons below 10 keV collide with pure thick targets of Al,Zn,Nb and Pb were studied.The paper concludes that the existing online method is only suitable for low-Z targets,and the methods developed in this work are applicable to all low,medium,and high-Z-thick targets;Based on solid Ne advanced 22Na slow positron beam device,the beam intensity is not stable and may even fluctuate greatly.It is necessary to apply the new method developed in this work to monitor the beam intensity online.