Based On The Research Of γ Spectrometer LED Stabilization

Nal scintillation spectrum is easily affected by the change of the external environment temperature and will produce the change of zero and gain, eventually leading to the measured spectrum drift, the stability of the spectrum is guaranteed by steady spectrum method.Domestic stabilizer often use the built-in reference source, and the reference source radioactive will have the side effect to human body, they use LED as the reference source radioactive to control the stability of the spectrum at abroad, the LED light after photo-multiplier tubes, get a peak position, using it to achieve the effect of the stabilizer.Photo-multiplier tube (PMT) can use the stability of the light emitting diode (LED) as a reference illuminant. Led offers clear light of short pulse voltage if the LED temperature keeps constant. However, if the photo-multiplier tubes should be performed in a wide temperature range, the LED light output is not a constant, but it is a function of junction temperature.In this article, through SMT32 as LED driver, and using the PID control algorithm. This problem can be solved at low expense by means of a new method. The LED is operated in two alternating pulse modes distinguished by the pulse voltage. The LED light output depends on the pulse voltage and, therefore, the PMT pulse height spectrum shows two distinct peaks. However, not only is the total amount of light L emitted per pulse but also the shape of the temperature dependence L(T) varies with the pulse voltage. The numerical ratio R of the peak positions corresponding to the two differem LED modes is therefore a function of the LED temperature as well. Since it is a ratio, R is independent of the actual PMT gain but characterizes the LED junction temperature. Thus, the pulse height ratio of the different LED signals can serve as an LED thermometer. Moreover, measuring L and R at several temperature points covering the full operational range yields a calibration function L(R). With this knowledge, commercial off-the-shelf LED components can be used as precise reference light sources in a wide range of ambient temperatures.