Preparation And Test Of ¹⁴N Injected Target

The CNO cycle is the main source of energy for a star with more than 1.3 times solar masses in its main sequence star stage [1].When the temperature of the star is very low,the energy generation rate of the CNO cycle is controlled by the reaction rate of 14N(p,γ)15O with the slowest reaction rate in this cycle [2].In addition,14N(p,γ)15O also controls the CNO cycle time of massive stars and is an important tool for determining the age of globular clusters [3].Therefore,it is of great significance to accurately measure the cross-section of 14N(p,γ)15O reaction.There are two main factors affecting the accurate measurement of the14N(p,γ)15O reaction cross section: one is the interference of natural cosmic rays.In order to reduce the impact of cosmic rays on the accurate measurement of 14N(p,γ)15O reaction cross section,we choose to conduct experiments in Jin Ping deep earth laboratory,which is located 2400 meters underground and surrounded by marble and radioactive stable rocks,which greatly reduces the background interference caused by cosmic rays on the measurement of 14N(p,γ)15O reaction cross section.The other is interference with nitrogen isotope reactions.The natural abundance of 14 N and 15 N is 99.63% and 0.37% respectively [4],but the cross-section of 15N(p,αγ)12C in this energy region is about five orders of magnitude higher than that of 14N(p,γ)15O.Therefore,in the accurate measurement of 14N(p,γ)15O reaction cross section,the preparation of a high-purity 14 N target becomes the key factor of the whole experiment.The main work of this paper is divided into the following four aspects: First: in September 2018,we prepared three 14 N injection targets on the tantalum(Ta)substrate on the 320 k V high-charge high-voltage platform of the institute of modern physics of China,using 14 N beam with energy of 100 ke V.Due to the use of analytical magnets in the experiment,15 N and other impurities along with 14 N beam were separated,so the purity of 14 N target prepared by this method was relatively high.Due to the high purity of the 14 N target prepared by this method and the ion beam injection method,this target is later referred to as the high-purity 14 N injection target(the schematic diagram of the sample is shown in FIG.3-6).At present,the preparation of high-purity isotope targets in the world is carried out by ion implantation,that is,ion beam precipitation.Second: in the process of preparing a high-purity 14 N injection target on the 320 k V high-charge high-pressure platform of the institute of modern physics of China,the influence of oil and gas generated in the process of vacuum-pumping on the purity of 14 N target was verified by adding liquid nitrogen into the cold well in front of the vacuum target chamber.When target 1 is prepared,liquid nitrogen is not added to the cold well.When target 2 and target 3 are prepared,liquid nitrogen is added to the cold well and supplemented every 1 hour to prevent the complete evaporation of liquid nitrogen,and the cold well cannot condense the oil and gas in the pipeline.Third: in June 2019,we will be in China institute of modern physics 320 k V high electric charge of the preparation of high voltage platform 3 piece of high purity 14 N injection target and a clean without the injection of tantalum sheet to the 720 institute of Si Chuan university,with Rutherford Back Scattering analysis content and content with depth distribution of the target and vacuum target chamber before any cold well on the preparation of the purity of target is measured.Since Rutherford Back Scattering analysis is not destructive to samples,it is widely used in many fields.By Rutherford Back Scattering experiment to obtain energy spectrum analysis,we get: vacuum target chamber before there is cold well can well restrain the pipe of oil and gas with beam into the tantalum(Ta)on the substrate,and the vacuum target chamber without cold well before the target sample preparation will be embedded in the process of the carbon and affect the purity of target;The nitrogen content of target 2 was 1.422×1018atoms/cm2,and that of target 3 was 0.824×1018atoms/cm2.Fourth,through this experiment,we have a deeper understanding of the design of the preparation of high-purity 14 N injection target and the application conditions of Rutherford Back Scattering analysis.As this is the first time for our research group to conduct relevant research,there are some defects in the experimental design and analysis(for example: 1.Since we analyzed the high-energy end of the energy spectrum,the gap between the energy spectrum of the target sample and the high-energy end of the tantalum sheet represents the element content.Since target 1 contains two elements and the gap at the high energy end of the energy spectrum is the sum of the contributions of the two elements,the nitrogen content in target 1 cannot be analyzed.2.When the proton energy is 1750 ke V and the scattering Angle is 165 degrees,we can see two peaks in the experimental energy spectrum of target 1.Because the energy point we choose for the energy scale is only at the high energy end,there is an error in the degree coefficient used for the low energy section,so the accurate depth cannot be obtained.3.At the same time,because the tantalum substrate is very thick,the experimental count of carbon and nitrogen elements is superposition on the count of tantalum elements,so it is not conducive to use the peak of nitrogen and carbon elements to analyze the content and depth).This paper points out the defects in the process of experimental design and analysis,and gives solutions and Suggestions.