Development Of Low Power Consumption Digital Gamma-ray Spectrometer Based On CPLD

γray spectrometry is an important nuclear geophysical methods which is widely used in uranium exploration, geological mapping, oil and gas exploration ,In areas of radiation evaluation of the environment, analysis of radioactive sample, it also plays a important role. This article comes from major project of the national "863 Program" (No. 2006AA06A207).Traditional Gamma-ray Spectrometer mainly use analog technology to process signal, there are the following deficiencies: (1) Analog shaping circuit can not achieve the best shaping effect, and shaping parameters will be changed when parameters of analog components changed by ambient temperature, this type of shaping is not easy to adjust.(2) In the case of high counting rate, the spectrometer resolution goes down; the pulse through-rate becomes low.(3) As there are many analog modules, the system requires a high signal to noise ratio, then more linear power is used, which results in increasing system power consumption and making the battery-powered applications inconvenient. To overcome these shortcomings, in recent years, foreign country developed digital multi-channel spectrometer based on FPGA and DSP, but it is always large power consumption, this paper proposes low power consumption digital gamma spectrometer architecture based on CPLD. The instrument is mainly composed of the following components:(1) Signal acquisition board is based on CPLD + ARM, mainly to complete digital multi-channel pulse height analysis, ADC will digitize signal from pre-amplifier directly. Filtering, peak searching, pile up rejection (PUR) and other functions will be completedin CPLD. The final results of the analysis will transmitto the ARM, which is responsible for data transfer between the host computer and CPLD.(2) In order to improve the conversion efficiency of the entire power system, alldesignof power supply board is based on switching power technology, which will provide low noise,±12V,±5V and positive 9V.As ripple of high voltage have great influence on the detector output signal.To reduce ripple noise, an electronic filter is used at output of high voltage and it works well.(3) So as to analyze results output from the acquisition board, developed a host software on the platform of visual C++6.0, which is used forspectrometer sampling, displaying and simple calculations.After instrument design is completed, there are some tests on spectral resolution, pile up rejecting, stability and spectral drift, the main technical indicators are as follows: the energy resolution of 8.0% (0.662MeV); energy linear correlation coefficient R is 0.9995, Differential nonlinearity (DNL) is1.02%, integral nonlinearity (INL) is 0.51%; have a certain pile up rejecting capability; has good stability, working 8 hours continuously, peak drift is less than 2 channel.