| CdZnTe semiconductor detector is a new type of gamma ray detector which is developed recently, It has the characteristics of high resolution, large absorption coefficient, high detection efficiency, convenient use, small volume etc, and can work under normal temperature conditions. It without the phenomenon of polarization detection scope within the energy of 5keV ~ 2MeV, and easy processing, coupled with low noise charge sensitive amplifier, can be made into compact, high efficiency, high resolution gamma ray detection device.It widely used in security, medical diagnosis, industrial inspection, species identification and celestial X-ray telescopes, etc.At present, the domestic of CZT crystal has been the growth of a mature technology, can be relatively easy to get to meet all kinds of CZT crystals measurement conditions, so as to make it into a specific function of CZT detector. To get laboratory level of nuclear pulse signal and the spectral lines usually use charge sensitive amplifier and digital multi-channel pulse amplitude analyzer of foreign Amptek, Canberra and other companies,but fully developed and successfully applied in the nuclear signal chain of product design is relatively rare,what’s more,report about digital multi-channel pulse amplitude analyzer which can overcome the tail effec of tellurium cadmium zinc probe hole capture is sespecially rare at home. But the application research of tellurium zinc detector is still in its infancy, it has not yet become mature application solutions in many areas, therefore, this paper carried out the test experiment, the characteristic of CZT detector and according to the actual performance parameters of the detector, the design optimization of the front end of the signal readout circuit and digital nuclear signal chain, and it provides the basis for the practical application of CZT detector.Main research work in this paper is as follows.1. This paper has set up a test platform for the CZT detector and completed the main parameters of testing work. Take hemisphere structure detectors and CaptureTM plus structure detector for example, which is developed by northwestern polytechnical university(NPU) and e V companies in the United States, the size of both of them are 4mm*4mm*2mm.This paper tested the two detectors in different temperature by the leakage current of the relation between the bias and the junction capacitance with the relationship between the bias.Experiments show that the developed by NPU detector under the same temperature and bias of the leakage current is lower than the eV companies in the United States, and the junction capacitance is also less than e V companies in the United States.2. Considering the junction capacitance and leakage current detector parameters, matching of the detector and field effect tube(JFET), PCB layout and other problems. This paper use the typical folded structure design of the low noise charge sensitive amplifier(CSA).The charge-sensitive amplifier under normal temperature of 23℃ for 615 electronic noise and noise slope is 5.45 electronic/pF; When refrigeration to-32℃ for 391 electronic noise and noise slope is 4.51 electronic/pF.3.With high efficiency, high frequency switch power supply MAX668 chip as the core, combined with voltage doubling rectifying circuit, designs the high efficiency, small volume, low ripple of bias power supply, power up to 800 V, the bias in the output bias voltage 350 V, output current more than 400 m A, ripple is less than 6 m V.4.Chose the suitable electric refrigeration device TEC, and high efficiency control circuit was designed using the way of temperature feedback for cooling the CZT detector and CSA, in order to reducing the noise of the detector and improve the working resolution of CSA. Measuring with 241 Am source developed by NPU detector, refrigered detector and CSA to-20 ℃, without using the rise time identifying, resolution has been increased from 7.87% to 7.12% at room temperature,with the rise time identifying, resolution has been increased from 3.42% to 3.42% at room temperature. Thus it improved the system resolution obviously in low temperature.5. The lifetime of probe hole carrier in CZT is usually around 1 μs, less than the capture time collection of holes, making smaller pulse signal amplitude, and the universal peak shift to the left, the formation of the tail, resulting in a decline in energy resolution.In order to reduce energy resolution charge capture effect caused by system declines, the rise time digital discriminator is designed, it will screened off signal which is collected incomplete. With the use of a rise time digital discriminator, the resolution is improved obviouslly.With NPU detector, the resolution of the measurement of a 241 Am source at room temperature increased from 7.87% to 3.42%, the resolution of the measurement of a 137 Cs source increased from 2.11% to 0.96%. Therefore, adopting the rise time screening can significantly improve the resolution of CZT detection system.6.Combining with NPU and CZT detectors of eV companies in the United States, the low noise, low noise charge sensitive amplifier bias power supply, electricity production(TEC) of the control circuit, such as the rise time of a digital discriminator module are designed and a complete digital CZT spectrum acquisition system is setted up.Test performance of leakage current, junction capacitance, energy resolution, etc between the domestic(NPU) and abroad(eV companies in the United States) detector are compared. Measuring 241 Am source and 137 Cs source at different temperature, whether to adopt the rise time identify the energy resolution of different detector. Finally results is gived by measuring Eu-152 source, Ra-226 source and Co-60 source which is using detector of NPU without using rise time identify, test results shows that tellurium cadmium zinc detector can be used for low-energy gamma ray measurement system and used as a probe of nuclide identification device. |
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