影响X光源特性的参数研究

针对高能电子束撞击重金属靶产生轫致辐射光子, 利用蒙特卡罗方法详细研究了电子束半径与发射度以及靶的厚度对X光源特性的影响. 结果表明：电子束半径与发射度不仅是影响照射量的主要因素, 也是造成照射量分布不均匀的主要原因; 给定电子束, 存在一个靶厚度使得靶前1 m处的照射量最大. 因此, 在X射线成像系统的设计和模拟过程中, 应综合考虑电子束半径与发射度和靶厚的影响.

Parameters Affecting the Characteristic of X-ray Source

The characteristic of X ray source is one of the most important parameters on the image quality of radiography. The X ray source is composed of bremsstrahlung photons produced by the high energy electron beam impinging on the heavy metal target. The effects of parameters (include radius and emittance of the e beam and the target thickness) on the characteristic of X ray source are detailed by means of Monte Carlo method. It is shown that (1) giving a e beam radius, the exposure at 1m from the converting target increases and the uniformity of exposure distribution becomes bad, when the normalized emittance of e beam decreases; (2) for a given normalized emittance, the exposure uniformity becomes bad, when the e beam radius increases, but there exists an e beam radius under which the exposure at 1m is the largest; (3) in the case of zero emittance, enlarging the e beam radius can slightly improve the uniformity; and (4) given an e beam, there exists a target thickness which causes the exposure at 1m to be the largest. Therefore, the radius and emittance of e beam and the target thickness should be integrated with the design and Monte Carlo simulation for radiography.