一种减小X射线背向散射方法的计算机模拟

Computer Simulation on the Reduction of X-ray Backscattering

影像增强器内电极和管壳对X射线的背向散射将降低增强器输出图像的空间分辨率和对比度 .提出一种能减小背向X射线散射的方案 ,即在管壳和内电极表面采用蒸镀或其它方法制作一层很薄的铝膜 (如 80 μm) ,使其吸收背向散射X射线 ,并对此方案的实施过程进行MonteCarlo模拟 .结果表明 ,在X射线能量较低的场合 ,如常规医学诊断使用的X射线能量范围 ,这种方法效果明显 .当球管电压为 6 0kV时 ,可将背向散射X射线光子数降低到原来的 2 5% .但随着球管电压升高 ,高能量的入射X射线光子数增加 ,背向散射光子的能量也随之提高 ,铝膜对背向散射X射线光子的吸收将减小 ,从而使铝膜对背向散射的抑制效果降低 .因此 ,该方案并不适合X射线能量较高的场合 ,如工业无损检测中使用的影像增强器 .

The X-ray backscattering from the inner electrodes and the tube wall of an X-ray image intensifier (XRII) will degrade the spatial resolution and the contrast of an output image. In this paper a method was put forward to reduce the X-ray backscattering by forming a thin aluminum film (80μm) on the surface of the inner electrodes and the tube wall through evaporating or other techniques. This Al film can absorb the backscattered X-rays,having no adverse effect on the XRII. The validity of the method was verified by Monte Carlo simulation. The results show that the method can reduce the X-ray backscattering markedly if the incident X-ray has low energy, for example, the energy being used by the medical routine X-ray diagnosis. The number of backscattered X-ray photons will be reduced to 25% of the original when the X-ray tube potential is 60kV. With the increase of the tube potential, the number of the incident high-energy X-ray photons as well as the energy of the backscattered photons increase,however, the number of the absorbed photons decreases, which weakens the effect of the Al film on backscattering. So, this method is not suitable for cases involving the use of high energy X-rays, such as non-destructive detection in industry.