Research On LED Stabilization Based On Programmable Constant Current Source And Photoelectric Correction

Scintillation-based gamma spectroscopy is widely used in: physiological medical testing,environmental radiation measurement,mineral resources exploration,highenergy physics research,nuclear accident emergency treatment and other fields.In the process of energy spectrum measurement and analysis,after obtaining the original spectral line of the detector,it is necessary to perform pre-processing such as smooth noise reduction,peak finding,and stable spectrum to ensure the accuracy of content conversion,dose conversion and nuclide identification.Due to factors such as temperature,magnetic field,high voltage stability and electronic drift,the scintillator light yield,photomultiplier or electronic magnification changes,eventually leading to spectral line drift.Spectral drift can lead to errors in the calculation of the energy window;when multiple detectors are simultaneously measured,the resolution of the synthesized spectrum will decrease or even be erroneous;in some cases,the spectrum will overflow and the high-energy ray information will be lost.In the field of energy spectrum measurement,the research on solving the spectral drift problem is both a key point and a difficult point.In this paper,a light-emitting diode(LED)-based spectrum spectrometer stabilization method and circuit are designed and implemented.The control of LED luminous intensity is used to simulate the luminescence characteristics of gamma ray with different energy absorbed by the scintillator and its practical application.LEDs that can be used to simulate the luminescence properties of Na I(Tl)crystals were determined by theoretical calculations and experimental tests.In this paper,the LED is closely attached to the scintillator,so that the light emitted by the LED and the fluorescence emitted by the scintillator can be irradiated to the photomultiplier tube(PMT)to form an energy spectrum.The ARM embedded microprocessor outputs a pulse signal to quickly switch the constant current source circuit to drive the LED,so that the LED emits a pulse beam of a specific intensity and illuminates the PMT.The artificially introduced LED characteristic reference peak is obtained by a gamma spectroscopy by outputting a pulse current through the PMT.By adjusting the frequency,pulse width and constant current value of the ARM output pulse signal,the intensity and peak position of the LED characteristic reference peak can be adjusted,so that the LED reference peak is far away from the energy range to be tested,and the energy peak with appropriate intensity can be quickly obtained.The use of LED reference peaks eliminates the temperature effects of all electronics in the PMT and back-end,and enables fast stabilization with flexibility and ease of use.Due to the temperature drift and light decay effect of LED,long-term reliable operation cannot be guaranteed.For this reason,a precision optical integrator based on SFH2701 ultra-low temperature drift(0.01%/°C)photodiode and charge integration chip IVC102 is designed.It measures the change of light intensity emitted by the LED in real time,plays the role of calibrating the luminous intensity of the LED,and eliminates the problem of long-term drift of the LED luminous intensity.Since the LED stabilization spectrum can only eliminate the temperature drift problem of the PMT and the back-end electronics,it cannot eliminate the temperature effect of the scintillator itself.To this end,a large number of temperature tests were performed on the scintillator,and the temperature characteristic curve of the scintillator luminescence yield was obtained.The paper systematically studied the functional relationship between scintillator,PMT and electronic temperature coefficient and system spectral line drift in gamma spectrometer.The system spectrum drift of LED stability spectrum and scintillator temperature correction is studied,and a complete and practical LED automatic stabilization method is proposed.After testing,the program achieved a better temperature correction stability spectrum effect.In the energy spectrum measurement system with a spectral resolution of 2048 channels,the peak position generated by the gamma ray with a energy of 3.5 Me V is stabilized by this method,and the K-40 peak shift is less than ±2 channels during the 12-hour measurement period.There are three innovations in this article:1.A method based on LED to accurately simulate the luminescence of a scintillator after gamma ray irradiation is proposed.2.A precision optical integrator based on low temperature coefficient photodiode and charge integration chip is designed to correct the light decay and temperature effect of LED in real time.3.The relationship between scintillator,PMT and electronic temperature coefficient and system spectral drift in gamma spectrometer was systematically studied.The system spectrum drift after introducing the LED stabilization spectrum and the scintillator temperature correction is studied,and a complete and practical LED automatic stabilization method is proposed.The design scheme is applicable to a measurement environment where the reference peaks such as the aerial gamma spectroscopy measurement,the low background lead gamma spectroscopy measurement are not obvious,or the background spectrum is relatively complicated.