Study On Imaging Of Primary Proton Beam Spot Using Secondary Neutronsy

The spallation neutron source is a large-scale scientific research platform with international frontier multidiscipline applications.It is an important scientific research facility for studying the microstructure and natural laws of matter.The China Spallation Neutron Source(CSNS)was constructed by China government during the "Twelfth Five-Year Plan" period.Following the on-service spallation neutron sources of the United States,Japan,and the United Kingdom,It is one of the four large pulsed spallation neutron sources in the world.The CSNS provides a good experimental platform for domestically scientific and technological developments.The on-service spallation neutron sources in the world have the common feature that they use a high-energy and high-power proton beam to bombard a heavy-element target and generate a large number of neutrons through the spallation reaction.With the continuous increase of the target beam power of the spallation neutron source,the monitoring of the beam spot in front of the target becomes more and more difficult,and it is necessary to find a more effective method to solve this problem.This paper is based on the principle of pinhole imaging to study the beam spot imaging of high-power proton beams in front of the target.It is expected to be one of the methods to solve this world-class problem.It has very important application prospects for existing conditions or new high-power spallation target stations in the future.We have calculated the secondary neutron beam emitted from the back-streaming angle of the target surface,and obtained the image of the neutron distribution at a remote location using the principle of pinhole imaging.Then according to the correlation between the secondary neutron distribution and the proton distribution and using the image reconstruction algorithm,the two-dimensional distribution of the proton beam spot in front of the target is indirectly obtained.This method can keep the imaging system away from the strong radiation area near the target and prolong the lifetime of the imaging system;The imaging system at the remote location can be maintained without beam shutting down;It also has the ability of real-time monitoring for the real two-dimensional proton beam spot;Beam spot image is more intuitive and accurate.In this paper,the Monte Carlo simulation software FLUKA is used to simulate the process of high-power proton bombardment of heavy element targets.By recording and analyzing the coordinates and energy of the secondary neutrons,the distribution characteristics of the secondary neutrons are obtained.Compared with the distribution of the incident proton beam in front of the target,we confirmed that the secondary neutrons can reflect the distribution characteristics of the incident proton beam in front of the target.The best spatial resolution is about 1 mm.Through further analysis of the distribution of neutrons emitted from the target surface,the conversion relationship between the distribution of neutrons emitted from the target surface and the beam spot distribution of the incident proton beam in front of the target is obtained.The neutron beam spot distribution in the remote location is obtained using the principle of pinhole imaging.The remote neutron distribution is reconstructed by the ART algorithm,and the distribution of the incident proton beam spot in front of the target is obtained,which theoretically confirms the possibility of reconstructing the proton beam spot distribution in front of the target based on the principle of pinhole imaging.In this paper,based on the principle of pinhole imaging and the idea of secondary neutron imaging,the beam spot distribution of the incident proton beam is reconstructed.It is a novel method to solve the high-power proton beam monitoring in front of the target.This method is first proposed in the international spallation neutron sources.It has an important reference value for solving the problem of high-power proton beam monitoring,and has a good engineering application value in the future.