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1、Chapter 11X-rays(June 14, 2013) The concept of atomic structure in quantum mechanicsn = 1, 2, 3, 4, 5, K, M, N, O, P, l = 0, 1, 2, 3, 4, 5, , (n 1) s, p, d, f, g, h, Therefore, in Element periodic Table K (n=1) L (n=2) M (n=3) N(n=4) s s p s p d s p d f Atomic Shells:The ground-state configuration (
2、组组态态，位位形形) of atoms.1s,2s,2p,3s,3p,4s,3d,4p,5s,4d,5p,6s,4f,5d,6p,7s,5f,6dn2(2l+1)1s2 2s22p6 3s23p64s1Potassium (K 钾钾)Z=19, Pauli exclusion principle: filling such quantum states:Coordinate rep.Quantum number rep.Quantum states for Hydrogen or lithium (Li, 锂）锂）1S11S22S11S22S1Another example: write th
3、e possible quantum states of 3p11S22S22p63S23p1X-rays diffractionCompton EffectX X射线三维成像可射线三维成像可显示心肌活动节律显示心肌活动节律http:/ 11.1 The fundamental knowledge and the production of x-raysX-rays are produced by electrons Electron accelerated by103 to 106V electrons with high speed strike a metal target x-rays
4、. observed by Rntgen in 1895 and named as Rntgen rays (伦琴射线伦琴射线). X-rays are electromagnetic waves The energy of x-ray photons is E = hv. Wavelengths of x-rays is 0.001 to 10nm.世界最强世界最强X射线激光器：比地球上光源亮射线激光器：比地球上光源亮10亿倍亿倍 http:/ 1.The equipment of the X-ray productionThe conditions of X-ray production:
5、 (1) high speed electrons beam (2) proper target to transform the kinetic energy of electrons into the energy of X-rays. The productive set of X-rays: milliammeterStep-up transformerStep-down transformer（filament）X-ray tubeGood heat conductor1% to x-rays99% to heat energyCathodeanode2. The intensity
6、 of x-raysThe intensity of X-rays: The intensity of X-rays is defined as the energies of x-rays passing through the unit area per unit time.Ni is number of hvi The intensity of x-rays depends on: (1) the tube current (more electrons more photons) (2) tube voltage (the energy of each x-ray photon). U
7、nder certain tube voltage, the current of filament (灯丝灯丝) control the intensity of x-rays. 3. The hardness of x-rays The hardness of x-ray is defined as its penetrating ability. Penetrating ability of X-rays depends on the energy of x-ray photons. The energy of x-ray photons depends on the voltage a
8、pplied to the x-ray tube. Therefore, the hardness of x-rays depends on tube voltage. 11.2 The X-ray spectrumThe plot of X-ray intensity versus wavelength of radiation emitted by an x-ray tube is called x-ray spectrum. n = 1 Kn = 2 LKLFrom higher energy levels X-rays production is involved in two dis
9、tinct processes: (1) continuous spectrum: Some of the electrons are stopped and deviated by the target. (2) Characteristic spectrum: electrons transfer their energy in whole or in part to the atoms of the target to excite the atoms. Cutoff wavelength11.3 The basic properties of x-raysThe general pro
10、perties of x-raysIonizing function X-ray enables the atoms and molecules to be ionized and this characteristic is quite useful in medical treatment. Fluorescence function (荧光作用荧光作用) : x-ray Fluoroscopy (透视透视) Actinic (光化学的光化学的) function: causing many chemical reaction. Such as x-ray photography biol
11、ogical effect: This function is the basis of radioactive (放射的放射的) treatment in medicine and also the reason to protect. penetration capability: Both x-ray Fluoroscopy (透视透视) & x-ray photography (摄影摄影) requires such function.11.4 The attenuation (衰减衰减) of x-raysWhen x-rays go through matter, various
12、interactions will be happened in the process. X-rays are absorbed by matter.The attenuation law of monochromatic x-raysWe use the word “monochromatic” as different matters have different abilities on absorbing different wavelength of x-rays.Where I0 is the intensity of x-rays and I is the intensity
13、of x-rays after penetrating through the x thickness of matter. is the linear attenuation coefficient. For a specific matter, the attenuation is proportional to the density of the matter. Because of this, the mass attenuation coefficient, m, could be defined, denoted asUnits of x, cm, , cm-1It can be
14、 used to compare the absorbing abilities among different materials. If we introduce the mass thickness xm = x, the attenuation equation could be written as Units: xm (gcm-2) , m (cm2 g-1) The thickness or the depth which could absorb the half amount of incident x-rays is called half-value depth (or
15、thickness). (半值厚度半值厚度Or半衰减层半衰减层厚度厚度) : I = I0 /211.5 Applications of x-rays to medicine1.Treatment 2.The x-rays used in clinic treatment is mainly for cancer. 3.X-rays can induce a series of biological effects in human body (ionizing, Compton effect, producing electron-positron pairs). 4.The functio
16、n of x-rays can kill cancer cells or at least can reduce their fission speed.2.DiagnosisFluoroscopy (透透视视) and photography (摄摄影影) : Homogeneous intensity of x-rays Non-Homogeneous intensity of x-rays Human bodyDifferent absorptionsnegative film fluorescent screen Digital subtraction angiography (数字减
17、影血管造影数字减影血管造影)Taking photosDigital Taking two photosOne normalOne with contrast mediumDo subtraction3.X-CT Computerized Tomography (X射线射线断层摄影术断层摄影术)CT shows：subarachnoid hemorrhage (蛛网膜下腔出血)How to get the image?1.Basic principle of CT: 2.(1) As different tissue has different absorbing coefficient an
18、d different thickness also has different absorbing coefficient , the coefficient are taken as a parameter. 3.(2) The principle is to set up the distribution of the coefficient in each part of every layer of the material in question and using computer to reconstruct the image of the material.Reconstr
19、uction of image 1 2 3 4 n-1 n.lIn11122122每次照射可以到每次照射可以到In，可算出，可算出 的和的和891075So we have: 3 5 7 24.CT Scanner5.CT Scanner: Computerized Tomography Scanner: an x-ray machine that can produce stereographic images (former name: CAT Scanner (Computer-Aided Tomography)PET: positron emission computerized tomography Classroom Quiz: (1) Write the ground-state configuration (组组态，位形态，位形) of Boron (硼硼) with Z = 5.(2) Write the possible electronic quantum states that could be possible taken for the outmost sub-shell electron of Boron.
