第14章-X射线-中文2.pptVIP

* * 第十四章 X射线 14.1 X射线的产生 Equipment Generating X-Rays (1)X射线管 (2)低压电源(5~10v) (3)高压电源(104~105v) 一、X射线的发生装置 条件：高速带电粒子流及合适的障碍物，将动能转换为光子的能量。 X射线管结构： (1) 灯丝 (阴极) - K A X-Ray X-Ray tube (2) 靶 (阳极) (3) 高真空管 (1)灯丝形状 电子流的截面“A” 阳极靶：耐高温、导热好性的材料。降温的方法：散热片通风、阳极空心内流水、旋转。 (2) 靶与电子流的角度“θ”. Small one - for diagnosis Large one - for therapy 影响焦点因素 A θ 有效焦点 焦点：实际焦点和有效焦点 Focal spot 实际焦点 (3) 电场的分布聚焦 二、 X-Rays 强度和硬度 1. X-Rays强度 I =? Nihvi=N1hv1+N2hv2+N3hv3+…… 2. X-Rays硬度 取决于光子能量的大小，与光子的数量无关。 hv 管电压U? Ve? hv。临床：KV 单位时间、单位面积的各频率的光子数总和N =? Ni。其正比管电流I。临床：毫安秒 The hardness means the penetrating ability of X-Rays which depends on the wavelength of X-Ray or the energy of X-radiation 三、 X-Rays 频谱 X-Ray spectra contains two portions: 1.连续谱 Continuos spectrum 2.线谱或标识谱 Line spectrum or Characteristic spectrum High speed electrons experience the action of electrical field of atoms in a target. Their velocities are reduced sharply and the energy of them may be converted directly to X-radiation. 1. 连续谱—韧致辐射 X-Rays最短波长 2. 标识谱—能级跃迁 nuclear Exciting inter electron High speed electron The wavelength of line spectrum only depending the element made up target and are independence of the tube voltage. So it’s called the characteristic spectrum. 序数越高能级差越大 X-Ray crystal · · · · Laue spot Proved the property of X-Ray Laue experiment （1912） 14.2 X-Ray Diffraction and the Structure of Biological Molecules 1. X-Ray diffraction on the crystal ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? d d? d?? ? ? dsin? 1 2 A C B d : inter- atomic spacing ? ? ? ? ? ? ? ? d Ex.1 The interatomic spacing is 0.2 nm and the plane angle is 10°. If the shortest wavelength in the X-Ray beam is 0.03 nm. Which wavelengths will be reflected strongly from this plane? Solution: ? ? ? 2. The Structure of Biological Molecules Given: ?、? , can measure d — Crystal structure X-Ray X-Ray spectrum contain information: Locations: d, λ,Ф, - structure Intensity: chemical compositio