The Design Of Gamma Spectrometer Based On The High-speed Acquisition Card

Multi-channel Gamma Spectrometer is a radiometer which is used to measure energy distribution and radiation dose of gamma rays. Multi-channel Gamma Spectrometer is made up of three parts which include detector, pulse height analyzer and record & display circuit. The detector will transform rays of different energies to corresponding electrical pulses which are magnified when it is working. The magnifying pulse is sent into pulse height analyzer to be separated and recorded by the record & display circuit. The gamma spectrum measured by the instrument can not only used by the environmental radioactivity monitoring, but also used to measure the content of uranium, radium, thorium and potassium in rock or stratum.There are three methods which are linear discharge, dedicated A/D method and high-speed A/D method according A/D converting ways. The high-speed A/D method is applied in the system. Compared to the previous two methods, high-speed A/D method has obvious advantages, which include the following parts. Firstly, it reduces the analog part of shaping circuit to make it no longer pass through peak hold circuit and peak detection circuit. Secondly, it achieves nuclear pulse signal's digital analyzing, besides, the flexibility and immunity of data processing is good, and the passing rate of pulse is high. Thirdly, it can achieve all-digital sampling, and can increase the results'accuracy of the follow-up process greatly. Because the entire waveform of pulse is sampled, the demand of rate of the A/D conversion circuit is high. The research selected Advantech's PCI-1714U high-speed A/D acquisition card, whose main features are that the rate of sampling is high, the rate can is up to 30M/s, and it can sample by four-channel simultaneously.The system consists of three parts which are front-end shaping circuit, high-speed A/D acquisition card and data processing procedures. The main function of front-end shaping circuit is to magnify, form and process detector's pulse, and make nuclear pulse transform to Gaussian pulse which can be processed easily, generating trigger which is synchronous to pulse signal meanwhile, and then send the trigger into high-speed capture card. Shaping circuits include signal linear amplifier circuit, pole-zero cancellation circuit, programmable amplifier, active integral filter circuit, baseline recovery circuit, and pulse amplitude discriminator circuit. At the same time the front shaping circuit board integrates the power module, the microcontroller and peripheral circuits. The microcontroller achieves communicating with the host computer and part of digital functions of shaping circuit. The functions include receiving programmed magnified instruction, receiving screening threshold instruction, and hyperbaric dynamic displaying. High-speed A / D acquisition card is to carry the sampling of pulse out. The functions include receiving the trigger signal to acquire data by specifying the mode and making data upload to the data processing procedures. Data processing sofeware of upper computer is written using LABVIEW, and it can achieve data receiving, processing and displaying. The functions of this software include driving capture card to sample at high-speed, receive the data from acquisition card, digital analysis of pulse height , drawing spectrum line, and stabilizing the spectrum and recording the spectrum line data through software and hardware.