圆柱法测量X射线管焦点尺寸的研究

文章基于EN 12543标准的边界法原理，提出了一种X射线管射线束不同张角处有效焦点尺寸测量的方法——圆柱法，采用双钨合金圆柱、像素100 μm的面阵探测器、平移和旋转机构对COMET公司的MXR 225HP/11工业X射线管大、小焦点进行测量。提出了一种测量X射线源焦点到平移旋转机构的距离及射线束不同张角处位置参数的方法。测量结果表明，该方法不仅可方便地测量焦点尺寸，而且能测量射线束张角范围内焦点尺寸的变化，并对其变化规律进行研究，这将对X射线管的焦点设计及其性能评价提供参考。

Research on Cylinder Method for Measuring Focal Spot Size of X-ray Tube

The focal spot size of X-ray tube has great impact on the image quality in radiographic testing. Typical EN 12543 standard gives five measuring methods (scanning method, pinhole camera radiographic method, slit camera radiographic method, edge method and measurement of the effective focal spot size of mini and micro focus X ray tubes) for focal spot size of industrial X ray systems. The testing conditions and equipment of these methods are complicated except the edge method. However, the edge method cannot be used for an absolute measurement of the focal spot. It is only useful for the checking of focal spot under field condition in order to find change of the focal spot. Based on the edge method of EN 12543, an innovative method called cylinder method for the absolute measurement was proposed in this paper. This method was different from traditional measurement of the focal spot perpendicular to X-ray emission direction called nominal focus. It could measure the focal spot size at arbitrary angle within the field angle of radiation beam by using shift-rotation mechanism. In this experiment, the focal spot size of MXR-225HP/11 was measured by double tungsten alloy cylinder and 100 μm pixel area array detector. Double tungsten alloy cylinder could reduce the influence of scattering and the spacing between two cylinders was designed to be variable in preparation for future research on the silt camera radiographic method. Pixel area array detector overcame the shortcomings of film photography and was convenient for computer image processing. In order to improve the accuracy of measurement, a calibration method for measuring the distance parameter from the focal spot to the shift rotation mechanism and location parameter at arbitrary angle was proposed. By measuring the large and small focal spot size of MXR 225HP/11 at different angles in the width and length directions, it is found that the focal spot size varies with angle and nominal focus sizes agree well with those measured by pinhole camera radiographic method provided in the manual. However, the variation law of effective focal spot size with angle in the width direction is quite different from the theoretical analysis results, and the reasons need to be further explored. The results show this method can accurately measure the nominal focus size but also the focal spot size variation within the field angle of radiation beam which will provide reference for the design of focal spot and performance evaluation of X ray tube. Besides, the layout of imaging system can be optimized by the variation of focal spot size to ensure high imaging quality.