| The miniature transmission X-ray tube is widely used in energy dispersive X-ray Fluorescence Analysis(EDXRFA). The miniature transmission X-ray tube with a small,low power consumption, X-ray emission efficiency that can be made the excitation source of handheld X-ray energy dispersive fluorescence analyzer. Miniature transmission X-ray tube is a vacuum state inside with complex structure. In the small space integrated electronemitting device, a magnetic focusing system, target and exit window. Miniature transmission X-ray tube add high voltage power supply device and a cathode current supply means. It is a precision and expensive device.The basic principles of Miniature transmission X-ray tube is a cathode emits electronsby high voltage electric field between the cathode and anode acceleration,bombarding the target on the anode to produce X-rays. Energy electron bombardment target will produce a continuous bremsstrahlung, characteristic X-rays emitted by the target brems-strahlung spectrum superimposed on the formation of Miniature transmission X-ray tube primary level spectrum. In EDXRF analysis, primary X-ray energy is usually required in the absorption limit must be greater than the atomic absorption of the target element. The primary X- ray below the absorption limit will be the background of the X- ray instrument spectrum. Relatively high radiation absorption limit rate of primary X-ray will not only affect the accuracy and sensitivity EDXRF analysis, so EDXRF analysis more difficult, and may even cause the detector electronics line load is too high.Thus, in EDXRF Analysis want to minimize the exposure rate of absorption limited primary, meanwhile must ensure that absorption limit above primary X-rays with higher volume ratio.The thesis stems from major national scientific research equipment development project "deep resource exploration core equipment research and development"(item number: ZDYZ2012-1) and National High Technology Research and Development Program(863 Program) resource environmental technology issues relating to the project "high-precision ray spectroscopy detection equipment research and development "(project number: 2012AA061803).From EDXRF analysis of actual needs, research miniature transmission X-ray tube emission spectrum characteristics, and try to miniature transmission X-ray tube is placedoutside the exit aperture filter, in order to reduce X-ray dose below absorption limit rate, At the same to ensure that the above absorption limit X-ray have a higher exposure rate. According to the X-ray absorption characteristics of the material, the selected aluminum as the base metal, copper, nickel, zinc, three metal filter element is added as a filter material of different content of the alloy and the thickness of the different miniature transmission X ray tube influences emission spectrum.Through theoretical calculation and analysis of the aluminum filter for Miniature transmission X-ray tube influences emission spectrum, based on the theoretical analysis of the establishment of the Monte Carlo model for simulation. According to the results of Monte Carlo simulation, drawn aluminum-copper alloys, aluminumnickel alloys,aluminum- zinc alloy optimal mix ratio and optical effect, the following conclusions:aluminum- copper alloy is used as filter material, most copper content of 10%, the best of aluminum- copper alloy having a thickness of 150 um, this time energy X-raycounts in the range of 0 ~ 10 KeV only energy X-ray counts in the range of 10 ~ 35 KeV 4.97%, taking into account the X-ray exposure rate and reduce X-ray exposure rate is within the range of 0 ~ 10 KeV request within 10 ~ 35 KeV energy range. Alum-inum- nickel alloy is used as filter material, optimal nickel content of 10%, the best aluminum- nickel alloy having a thickness of 100 um, energy is in the 0 ~ 10 KeV X-ray counts only the energy range 7.37%,X-ray count within 10~ 35 KeV range. Aluminum- zinc alloy is used as filter material, the best zinc content of 15%, the best aluminum- zinc alloy having a thickness of 100 um, energy is now in the range of 0 ~ 10 KeV count X-ray energy in onl-y 10.7%,X-ray count within 10~ 35 KeV range. |
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