Development And Application Of X-ray Instruments With Li F Full Focuse Double Curved Crystal

Full focuse double curved crystal(DCC)has two radii of curvature,including Rowland circle and rotation direction around focal point line.DCC is a strict Johansson-type structure.The radius of crystal is R and the radius of crystal lattice plane is 2R.It diffracts monochromatic X-ray which Bragg's Law was satisfied and totally foucused it to the focal point on Rowland circle.The combination of DCC and microfocal spot X-ray source can diffraction high-intensity monochromatic X-ray and converge.This monochromatic X-ray fluorescence spectrometer(MWXRF)is a development direction of energy dispersive X-ray fluorescence spectrometer(EDXRF)which has obvious advantages in material elements analysis.MWXRF uses monochromatic X-rays to selectively excite elements in the material,thus can lower the limit of detection(LOD)by1?2 orders of magnitude.Laboratory type monochromatic X-ray source can be provided by combination of microfocal spot Xray tube and fully focused DCC which will be able to replace some applications of synchrotron radiation source.According to the DCC principle,a complete set of procedures and methods for LiF crystal grinding,crystal curving,instrument design and application are established.The main research contents are as follows:1.Based on the Bragg equation and the Johansson Roland circle,the radius of the Rowland circle R and the monochrome X-ray energy E were set.The crystal parameters including the Bragg incidence angle,the rotation radius r,the distance between source and crystal and crystal to sample,the distance of focal line and so on,are calculated firstly.Using the craft of " grinding first and then bending",the planar crystal parallel to lattice plane was grinded to a cylindrical surface with a radius of curvature of 2R,and then gradually increased 2?4kg load on the punch under650?700?,so that the cylindrical crystal was slowly deformed,finally the DCC surface was consistent with the concave die.The practical parameters of DCC were fully identical with the theoretical value.Through this craft,50mm×30mm×0.5mm LiF(200)with a 5.415 keV diffraction energy,42mm×22mm×0.5mm LiF(200)with a 17.425 keV diffraction energy,54mm×30mm×0.5mm and 40mm×30mm×0.5mm DCC with a diffraction 17.425 keV energy were fabricated.And the diffraction energy can be extended to any monochromatic X-ray energy in the energy range of2.30?22.16 keV.The DCC need to be adjusted by means of three dimensional optical adjusting frame.The intensity measuring device was designed to test the diffraction intensity of LiF(200)DCC,which reachs 5.3×108cps international level.The knifeedge scanning test was carried out to measure the focal spot with Ti sheet.During the experiments,it was found that the size of the calculated focal spot showed a good quadratic linear relationship with the step distance,and the size of the calculated focal spot showed a good quadratic relationship with the Z-axis position.According to the fitting curve,the minimum size of the horizontal focal spot was 0.74 mm.The theoretical minimum focal spot size at the sample window is 0.24mm×0.52 mm considering the 34.6° angle between the convergent X-ray beam and the sample.2.Development and application of MWXRF instruments for light elements.Double arc slits,light matrix or pure copper sample window,small aperture and copper collimator with aluminum inside were used to minimize stray line interference.MWXRF trace light elements analysis instrument was developed using LiF(200)DCC and micro-focal spot Cr target.The LOD of S in gasoline was 1.75?g/g,and the LOD of Cl in mineral oil was 0.63 ?g/g.3.MWXRF instrument for heavy elements has been also developed with LiF(420)DCC and micro-focal Mo target X-ray tube.It was successfully applied in analysis of Cr?Ni?Hg?As?Pb heavy metals in the tipping paper and filter of tobacco materials.The LOD of elements was reduced nearly an order of magnitude in which LOD of Cr declined from 7.5?g/g to 0.72 ?g/g.