Design And Realization Of The Gaussian Shaping Filtering In Digital Nuclear Instrument System

It is of significant importance to Extract and process nuclear information for the study of many basis and application sciences. An analog nuclear instrument system is formed from the standardization modules whose functions were defined and solidified in hardware by the manufacturers. The user cannot modify or optimize the functions of the standardization modules even if the measuring conditions had been varied. So some investigators start to explore and develop new nuclear instrument systems. The progress of digital processing techniques brings the chance for developing new nuclear instrument systems.In digital nuclear instrument systems, after the signal from detector-preamplifier is necessarily band-limited and gain-adjusted, it is digitized by high speed ADC at once, and then all signal processing are implemented in digital domain. A digital nuclear instrument system can carry out various nuclear measurement tasks by designing various digital algorithms. The user can modify the digital algorithms according to some special measurement demands so that the optimal results can be obtained. In the digital domain, as long as the signal features those hide information are recognized, one can extract the information from the signal features by digital processing techniques using certain methods.Corresponding to the time of radiation event happening, the radiation signal is of sharp transition, and the information of radiation events are hidden in the features of the points of sharp transition. The wavelet analysis is a novel method for signal processing and can be used to exhibit the features of the points of sharptransition in signal.In this paper, the radiation signal have been analyzed and processed using wavelet method in detail, and the techniques have been developed for the synthesis of the gaussian pulse shapes based on the wavelet analysis. The gaussian shaping filter(GSF) based on wavelet analysis has a distinct merit, which is that it can accurately extract energy information and time information from radiation signal at the same time. The peak amplitude of the gaussian pulse reflects the energy information for radiation ray, and the peak position of the gaussian pulse reflects the time information for radiation event happening.The GSF based on wavelet analysis is a band-limited filter. At the output of the GSF, the minimum mean square noise is obtained by choosing a suited scale, and so the best signal to noise ratio (SNR) is achieved.The noise corner constant rc and the exponent decay constant r0 have been evaluated using described methods, which help to design an appropriate GSF with more accurate characteristic parameters related to a radiation detection system. The evaluating precision of the exponent decay constant r0 has been effectively improved by denoising the noisy exponent signal with wavelet transform.The digital algorithms based on the GSF for measuring energy spectroscopy have been described. In the algorithms for pulse detection, besides traditional threshold, the minimum width MinWidth and the maximum width MaxWidth are used at the same time, which reduce the probability of mistaking for or missing out the valid radiation pulses. Making use of the linear phase characteristic of the GSF, a measurement of the peak amplitude of a pulse is simply obtained by capturing the value of the pulse amplitude at the output of slow filter channel at the pulse's arrival time tpeak which has been made sure in fast filter channel based on the pulse detection algorithms, which simplifies the procedure of capturing peak amplitude of a pulse. The pileup correction algorithms based on the GSF improve both the energy resolution and the pulse throughput for a radiation measurement system. Because the rate of output pulses closes to the rate of input pulses, it is not necessary at approximate case to correct the measured energy spectroscopyaccording to the dead time correction algorithms.The recursion approximation algorithms for realizing the GSF are described. The linear phase recursion approximation algorithms can extract energy and time information at the same time and well exhibit the excellent performance of the GSF. The linear phase recursion approximation algorithms need a mass of memory resources because of making use of anti-cause filtering. If only measuring energy spectroscopy, in order to reduce the demands of hardware resources, the nonlinear phase recursion approximation algorithms are provided in this paper, too.The digital system platform for measuring energy spectroscopy is formed using both the digital nuclear instrument system and the algorithms for measuring energy spectroscopy based on the GSF. It is validated that the digital system platform for measuring energy spectroscopy is efficacious by measuring energy spectroscopy in person computer with the simulating signals and the sampling signals. Contrast with the results from analog system for measuring energy spectroscopy, the energy resolution from digital system for measuring energy spectroscopy is obviously improved.