Time constant of double exponential signal for X-ray energy spectrum detector

Abstract

BackgroundIn the X-ray energy spectrum measurement system, the time constant is an important factor affecting trapezoidal pulse shaping. Accurate measurement of the time constant of double exponential pulse signals is beneficial to obtaining a better trapezoidal pulse shaping.PurposeThis study aims to propose a fast fitting double exponential pulse algorithm for measuring the time constant in trapezoidal pulse shaping.MethodsFirst of all, the linear regression method based on the least square method was adopted to convert nonlinear fitting linear fitting. Then, functional expression of double exponential pulse signal was fitted by fast trapezoidal pulse shaping, and the feasibility of time constant measurement in trapezoidal forming by fast fitting double exponential algorithm was verified by MATLAB programming simulation. Finally, the practicability of the algorithm was evaluated by experimental pulse data of 55Fe radiation source received by X-ray silicon draft detector (SDD). Goodness-of-fit R2 of this algorithm was compared with that of cftool toolbox of MATLAB on both the simulation data and experimental data.ResultsThe goodness of fit R2 of proposed algorithm exceeds 0.95 for both the simulated signal with 5% standard deviation noise and the shaped pulse signal of experiments. When the goodness of fit exceeds 0.95, the running speed of this algorithm is 2 orders of magnitude faster than that in cftool toolbox of MATLAB.ConclusionsThe algorithm of this paper possesses high fitting degree, fast calculation time, hence suitable for real-time measurement of time constant of double exponential pulse signal in embedded system.

Keywords

• micro-zone energy spectrum
• trapezoidal pulse shaping
• double exponential fitting
• least square method