Development Of An Energy Dispersion X-Ray Fluorescence Spectrometer

Energy dispersion x-ray fluorescence spectrometer (EDXRF) is an important nuclear analysis tool, which is widely used in the fields of geology, metallurgy, architectural material and environment. Resolution is an important specification of the EDXRF. Apart from the resolution of detector itself, the affection of the performance of the following electronic circuits upon the system resolution is also not negligible.In electronic circuit, the other factors that affect the energy resolution are noise, pulse pile up and ballistic deficit. This paper is focused on the design of the electronic circuits to improve the system energy resolution, including the design of the preamplifier, the shape amplifier, the base line restorer (BLR) and the multichannel analyzer (MCA), discussing some problems, which should be taken into account in the design. In the design of shape amplifier, a method based on the simulation function of MATLAB is used to choose the parameter of the circuit. It enhances the flexibility and reliability of the design and has some practicability.In the EDXRF, the stability of the spectrum has notable affection on the accuracy of measurements. The designed EDXRF has the function of automatic spectrum stability, which can reduce or even eliminate the affection of spectrum driftupon measurement result. This can be realized by means of monitoring and adjusting the programmable gam amplifier (PGA) to stabilize the gain of the amplifier system.Complex programmable logic device (CPLD), usually used to develop ASIC, is widely used in digital system to accomplish complex combinational and sequential logic. Developing the control logic with CPLD, we can design hardware through specific software, which would reduce the difficulty of the development. We can not only improve the reliability of the development, but also reduce time and cost. In this paper we discuss MCA circuit, the sequential logic for MCA data collection, for the setting of the ULD, LLD and the gain of PGA, as well as the combinational logic for decoding circuits of the computer interface, based on CPLD. All the sequential and combinational logics, tested though the simulation under the specific software, are proved to meet the requirements of the design. It is a good reference for accomplishing the MCA in practice.