Method for digitally correcting sodium iodide crystal decay time in real time

Abstract

The invention provides a method for digitally correcting attenuation time of a sodium iodide crystal in real time. The method comprises but is not limited to steps that S1, after rays are detected bya detector composed of a sodium iodide crystal and a photomultiplier, the photomultiplier outputs a current pulse signal of an exponential decay function waveform, the signal is defined as I(t), and the decay time constant of the crystal is tau0; S2, after the current pulse signal I(t) is converted by an RC feedback type charge sensitive amplifier, a double-exponential voltage signal is formed, moreover, the bandwidth of an input current pulse signal is reduced, and the signal is defined as V(t); S3, digital sampling of the signal V(t) is conducted through an ADC, and a digital pulse signal V(n) is formed and enters an FPGA to be subjected to digital signal processing. The method is advantaged in that whole process of the method for digitally correcting the attenuation time of the sodium iodide crystal in real time is automatically carried out, and the attenuation time of the crystal changing in a large range is corrected in real time within a wide temperature range; a spectral line drift phenomenon of the energy spectrum measurement equipment caused by crystal attenuation time change is greatly reduced.

Description

technical field [0001] The invention specifically relates to a method for digitally correcting the decay time of sodium iodide crystals in real time. Background technique [0002] According to the research data of Schweitzer J S, Ziehl W.Temperature Dependence of NaI(Tl)DecayConstant[J].IEEE Transactions on Nuclear Science, 1983,30(1):380-382, it is shown that sodium iodide crystals, namely NaI(Tl) crystals, decay The time constant is 230 ns at room temperature (25°C). If the temperature increases, the NaI(Tl) crystal decay time constant will slowly decrease. It is reduced to 100ns at around 180°C. If the temperature drops, the decay time constant will increase at an average rate close to 5ns / °C, about 600ns at -25°C, and the rate of increase will be faster and faster, which has a nonlinear characteristic. In a wide temperature environment, where the temperature range exceeds ~30°C to 60°C, the NaI(Tl) crystal decay time constant ranges from about 650ns to 200ns. Due to ...

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Problems solved by technology

[0003] The current common practice is to limit the operating temperature range of radiation measuring equipment based on NaI(Tl) crystals as detectors to not lower than -10°C, or even above 0°C, so that the influence of decay time changes is acceptable

Or set a longer ballistic loss recovery time (need to be greater than 5 times the decay time constant), but this increases the forming time and reduces the pulse passing rate of the system, so it can only be used at low dose rates

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