The Study Of Digital Nuclear Spectrometer Based On Gaussian Filter Shaping

The acquisition and processing to nuclear information have great application value in research of basic science and applied science. Because of its high precision and sensitivity, nuclear analysis technique has become an important part of nuclear signal detection. Moreover, it can detect information that other methods can’t. Due to the importance and high reliability of nuclear analysis, the development of nuclear spectrometer has being paid close attention to. Since the mid-1990s, with the development of integrated circuit and electronic technology, digitization has become the important direction of nuclear spectrometer. Digital pulse shaping technology has become the mainstream in the process of digitization of nuclear spectrometer. What’s more, it is the most active and important research field in recent years.Digital pulse shaping technology can not only improve the stability of digital nuclear spectrometer system, but also flexibility and adaptability. The stability of nuclear spectrometer system is mainly measured through signal to noise ratio, which can be improved by filtering, in which process output signal is shaped. So, aiming to promote signal to noise ratio, filtering is closely related to signal shaping. Currently, three kinds of digital pulse shaping technology are mainly used, they are triangle, trapezoidal and Gaussian filter shaping, in which the latest is the most widely used and of optimal performance. Pulse signal shaped by Gauss has good performance in the aspect of signal to noise ratio promotion, ballistic deficit reduction and baseline drift. In view of this, appropriate impulse response is designed to convolve with the exponential decay signal. Only in this way, the later can be processed to Gaussian pulse, of which the amplitude is proportional to the exponential decay signal amplitude.In addition, real-time is necessary in the process of Gaussian filtering shaping. The key to real-time processing is to design a finite impulse response digital filter, and to shape the exponential decay signal to Gaussian pulse through convolution. Then, algorithm should be improved to adapt to parallel computing, and multipliers and adders are cooperatively used to improve processing speed. In this paper, Gaussian pulse shaping algorithm is improved, and the arithmetic logic unit which has cooperative multipliers and adders is designed on a field programmable logic device (FPGA), realizing convolution and filtering of a sampling point within a clock cycle. This ensure real-time in the Gaussian pulse shaping.Aiming at the urgent need of digitalization of nuclear spectrometer, based on technologies such as signal amplification, high speed of data acquisition, real-time processing, digital Gauss shaping and design principles on FPGA, the paper completes hardware implementation on FPGA and finishes the design of digital nuclear spectrometer based on Gauss filtering shaping.Finally, the paper puts forward detailed tests on several important parameters, such as signal to noise ratio, accuracy and energy resolution. Moreover, the influence of signal to noise ratio to signal shaping and filtering is tested when shaping time increases. On the other hand, baseline deduction and stabilizer are researched. Based on a series of research, the conclusion is drawn that Gaussian filter shaping is feasible on the basis of the digital nuclear spectrometer.