大学物理实验报告英文版--X光

Experiment report of X ray Principle When we speak of attenuation of x rays we mean the decrease in intensity that occurs when the radiation passes through matter This attenuation is caused mainly by the two effects scattering and absorption Although absorption and attenuation are different physical phenomena the transilluminated object is often referred to inaccurately as an absorber this should more properly be termed an attenuator However this description will follow the traditional usage in some places and refer to absorbers instead of attenuators The scattering of x ray quanta at the atoms of the attenuator material causes a part of the radiation to change direction This reduces the intensity in original direction This scattering can be either elastic or entail an energy loss or shift in wavelength i e Inelastic scattering When x ray hits a fluorescence material it excites the material making fluorescence lights This is the principle of a fluorescence screen When x ray is used in imaging the transmitted light will carry interior information of the object A more sophisticated x ray detector is the so called Geiger Muller counter an instrument for detecting the presence of and measuring ionizing radiation such as the x rays It converts the intensity of the x ray into counting rates We will use such a device in our lab Attenuation of x rays When passing through a material x ray can be attenuated by E M interactions For a slab of thickness x the transmission defined as the ratio of the transmitted radiation to the incoming is the attenuation coefficient with a dimension of x Te 1 distance is a character of the material and it varies for example as a function of atomic number We will study this dependence in this lab Bragg Diffraction d a0 Like normal lights when x ray transmit through material with regular optical pattern e g lattice diffraction will happen if the wavelength of the x ray is close to the lattice space Such diffraction on the crystal is the so called Bragg Diffraction If the lattice spacing is d and the x ray and the crystal surface forms an angle the angle where maximum diffraction happens will satisfy 2 sin 1 2 dnn where n is an integer and is the wavelength Lab equipment The equipment is an x ray lab system made by Leybold Inc A schematic is shown below 监控区X光管实验区 B1 B2 B3 B4 B5 A1A2A3A4 此区内所有操作必须 带上手套进行 The x ray is generated by an electron beam with controllable energy via the potential and current The x ray is going into the detection chamber to the right There is a removable aperture which focuses the x ray a rotatable sample holder and a rotatable G M counter At the right end of the wall there is a fluorescence screen for imagine Operation details of the device will be given by the manual Basically you need to set the high voltage U which determine the energy of the x ray the current I and the angle of the sample holder target or the detector A knob can be used to make the adjustment on selected parameters Coupled movement means one moves the target and the detector together the former by an angle and the latter by an angle 2 Make sure the lead glass window is closed before you turn on the high voltage Attenuator target Left aluminum attenuator mounted on a curved plate with thickness of 0 0 5 1 0 1 5 2 0 2 5 and 3mm One can select different thickness by selecting angle Right attenuation of different materials all with a thickness of 0 5 mm including Polystyrene average Z 6 Aluminum 13 Iron 26 Copper 29 Zirconium 40 and Silver 47 2 Install the aperture Install the Zr foil onto the aperture This is to filter out the K line Squeeze the NaCl crystal onto the sample holder In this part of the procedure we need to make sure that the X ray beam the crystal surface and the detector is aligned Use the following alignment procedure by the Bragg Diffraction the process is omitted data The first peak appears when it s 7 5 degree 1 analysis 2 sin 1 2 dnn Then m 9 10 2 sin2 0 56402 10sin7 5 1 4724 10 1 d n That is the wavelength of X ray is m 10 1 4724 10 2 Measure the X ray attenuation to different thickness Install the Zr foil onto the aperture Set HV 21 kV I 0 05 mA 0 t 100 s Hit target key Change the angle sequentially to 0 10 20 30 40 50 60 degree the thickness of the attenuation increase by 0 5mm each step For each of this setting hit scan to take the data and hit replay to get the average rate attenuation of different thickness thickness mm 0 511 522 53 Data 1 s 21 49 64 42 81 71 Fit the rate as a function of thickness with background subtraction to get the attenuation coefficient Fit the data in origin with exponential fit mode expdec1 through equation We form the graph of 1 T and x So we get that x Te Hence So the attenuation coefficient is 11 0 26378 3 79097t Measure the X ray attenuation to materials with different atomic mass a Remove the Zr filter Insert the curved attenuator holder B different target into the annulus slot on the plastic mount Set HV 30 kV I 1 mA 0 t 100 s Hit target key Change the angle sequentially to 0 10 20 30 40 50 60 degree each corresponding to a given material b For each of this setting hit scan to take the data and hit replay to get the average rate c For the scan with Zr filter attenuation of different Z with Zr Z61326294047 Data 1 s 9117 97627 472 97 7108 914 4 No exact rule can be found Install the Zr filter Repeat of Z number The graph turns out attenuation of different Z without Zr Z61326294047 Data 1 s 9025 49027 88308 475 25 274 8 Plot the rate as a function of Z number Also no exact rule can be found Conclusion 1 the wavele