Research And Relization Of Effective Focal Spot Size Measurement Method In Electron Linac

Industrial computer tomography technology(referred to as Industrial CT) has been called one of the most promising technologies of the nondestructive testing because of its clear and accurate detecting about internal structure of objects. Electron linac owns the characteristics of high energy ray beam and strong penetrating power, which make it widely used as a high-energy radiation source in industrial CT system. The size of effective focal spot is one of the key performance indicators of electron linac, affecting spatial resolution and unintelligibility of industrial CT images directly. As a result, it is necessary to accurately grasp effective focal spot size of electron linac radiation source when high-energy industrial CT system is developed.Currently,traditional measurement methods about effective focal spot size of ray source are scanning method, pinhole method, sandwich method, etc. However, these methods do not apply to measure effective focal spot size of electron linac, or these methods susceptible to interference of subjective factors in the measurement process leading to poor reproducibility.To solve these problems, the influence that effective focal spot size of electron linac has on the quality of industry CT image is analyzed. Three methods of measuring effective focal spot size of electron linac are researched and put forward referring to the characteristics of detection and scanning of ICT, including vertical scanning method; parallel scanning method and angle translation method, which are objective, quantitative and easy to be implemented. Then requirements and detailed procedures of three measurement methods are introduced, and advantages and disadvantages are compared.To achieve the measurement method, effective focus size measuring instrument of electron linac is developed. According to the performance requirements, systematic framework of instrument measuring effective focal spot size is analyzed. To meet the detection and acquisition task of high-energy X-ray, the design of detection-acquisition system of effective focus size measuring instrument are researched, and the hardware circuit and control logic of detection-acquisition system are implemented. In order to meet the control tasks about effective focus size measuring instrument, the solutions of control system are researched, and the hardware circuit and control logic of the main control board of control system are completed.Then, the debugging of the detection-acquisition system, the control system and online debugging about measuring instrument are carried in turn. The test results show that the measuring instrument can meet the demand of measurement about effective focal spot size of electron linac with high reliability and accuracy.Measuring experiments about vertical scanning method, parallel scanning method and the angle translation method are carried on the 4Me V electron linac. And experiment about sandwich method is also carried out as a contrast. The experimental results show that the vertical scanning method and parallel scanning method can both complete the tasks of measurement about effective focal spot size of electron linac effectively, and parallel scanning method has a better measurement accuracy. Relative to other methods of measuring effective focal spot size of electron linac, the measuring methods put forward this paper are less susceptible to the effects of subjective factors and easy to be operated and implemented with high measuring accuracy.