A Digital Alpha/Beta Ray Discrimination Method

Abstract

A digital alpha / beta ray discrimination method. After the alpha / beta rays are detected by the detector, the photomultiplier tube outputs a current pulse signal, which is converted by an RC feedback charge-sensitive amplifier to form a double-exponential voltage signal, which is then digitized by an ADC. The digital pulse signal enters the FPGA for processing; uses the current waveform restorer to eliminate the long exponential decay signal formed by the RC feedback charge-sensitive amplifier; uses the construction of two parallel digital square filters, according to the decay time of ZnS(Ag), plastic scintillator Set the filter width to process the output signal of the current waveform restorer; the peak value holder automatically tracks and outputs its peak value for the square filter; the ratio comparator is used to obtain the ratio of the two peak holders, and the α counter that exceeds the set threshold Counting is performed, and the β counters below the threshold are counted. After the α / β rays are discriminated, the counting auto-increment enabling signals of the α and β counters are generated. After receiving the auto-incrementing enabling signals, the counting task is completed.

Description

technical field [0001] The invention belongs to the technical field of ray measurement, and specifically relates to a method for screening α / β rays. Background technique [0002] The α / β surface contamination instrument and the low-background α / β measuring instrument can use a composite scintillator composed of ZnS(Ag) and a plastic scintillator and a photomultiplier tube to form a probe to simultaneously detect α / β rays. ZnS(Ag) has high detection efficiency for α rays, but is insensitive to β rays. β rays can penetrate the ZnS(Ag) coating and reach the plastic scintillator to be absorbed. The photons emitted by the composite scintillator are converted into current pulse signals by the photomultiplier tube, and the current signals can be processed by the post-stage signal processing chain. The current pulse signal sequence has both alpha signals and beta signals. The post-stage signal processing chain must deal with both. The pulse signal is screened in real time, and the ...

AI Technical Summary

Problems solved by technology

For the amplitude method, since the α and β signals have a relatively large overlap in amplitude, there will be mutual crosstalk for the rays in the overlapping area, and since the judging standard is the amplitude, the gain stability of the entire system is very important for the particle screening. Great effect

For the pulse width method, the pulse amplitude and baseline noise have a greater impact on the determination of the start and end positions of the pulse, resulting in inaccurate measurement of the pulse width and affecting the particle screening effect

For the above two methods, there are common defects. The key screening parameters are controlled by analog devices. In the amplitude method, the amplitude of the pulse is greatly affected by the photomultiplier tube and the amplifier circuit, and the threshold is affected by the stability of the reference voltage; In the pulse width method, the pulse width is affected by the peripheral components of the photomultiplier tube

When the environment changes and the device ages, these key parameters will change, and the stability of the entire screening effect will be affected

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