Study On Spectrum Smoothing Technique In Positron Impact X-Ray Spectrum

Positron is the antiparticle of electron.From theoretical prediction to experimental observation,it has been widely concerned by scholars.The collision between positron and atom has attracted a large number of scholars to do related research,and has become one of the important parts of nuclear physics.However,the interaction mechanism between low-energy positrons and other substances is still unclear,and a large number of experiments are still needed to reveal the mystery.The positron induced inner shell ionization cross section data are widely used in practical research.A large number of reliable experimental data are needed in many fields,including radiation physics,astrophysics,plasma physics and so on.However,the experimental data of low-energy positrons are still very scarce,and there are some differences between the experimental results and the existing theoretical models,so more reliable experimental data are needed to guide the improvement and development of the theory.At the same time,the development of advanced data processing methods can not only improve the efficiency of experimental data processing,but also improve its reliability.In the experiment of studying positron impact ionization cross section by characteristic X-ray method,it is important to obtain accurate characteristic peak net count in data processing.However,the fluctuation of experimental X-ray spectrum is increased due to annihilation effect.Especially for the experimental spectrum with low incident positron energy is more affected by the statistical fluctuation,which makes it difficult to obtain the characteristic peak net counts and seriously affects its accuracy.In order to eliminate this adverse effect,we propose to smooth the positron impact X-ray spectrum.By using different smoothing methods to fit or transform the original spectrum lines,the amplitude of statistical fluctuation is reduced,which not only improves the efficiency of data processing,but also ensures the accurate acquisition of characteristic peak net counts.Based on MATLAB GUI platform,an X-ray spectrum smoothing software is developed in this work.We can choose gravity center method,least square method,Fourier transform method or wavelet transform method to smooth the X-ray spectrum impacted by positron and calculate the corresponding characteristic peak net counts in real time.The program can free to choose the smoothing interval,smoothing degree,characteristic peak boundary,which also can smooth the experimental spectrum efficiently and reliably.This paper also establishes a reliable evaluation system to evaluate the smoothing effect,and the evaluation parameters will be given in real time in the spectrum smoothing program to facilitate timely adjustment.The evaluation system has also passed the reliability verification,and the reasonable range of evaluation parameters is given.The best smoothing scheme can be selected through the evaluation system to achieve the optimal smoothing effect.In this work,we also used the developed spectrum smoothing program to smooth some experimental X-ray spectrum of positron collision by different methods.According to the evaluation system,the smoothing effect of different methods has been evaluated,and the best smoothing scheme has been selected and the corresponding characteristic peak net counts of the experimental spectrum after smoothing has been calculated.Among them,the experimental X-ray spectrum of 4-9keV positron collision Al target is less affected by statistical fluctuations and using the center of gravity method can achieve great smoothing effect.Moreover,the net counts gap of characteristic peak calculated by each scheme is not large,and the effect of energy spectrum smoothing is relatively not obvious.In the experimental data processing of 6-9keV positron impact Ag target,the background energy level is reduced due to the double Si escape peak found in SDD.There is a small impurity peak near 3.5keV in the experimental spectrum,while the characteristic X-ray energy corresponding to the Lγ1 peak in the Ag target experimental spectrum is about 3.5keV.In order to read the characteristic peak information more accurately,it is necessary to deduct the impurity peak.It is observed that there are the same impurity peaks near 3.5keV in the experimental spectrum of Al target.Therefore,using the Monte Carlo simulation method to calculate the normalized constant of the two,and then the normalized Al target experimental spectrum is deducted from the Ag target experimental spectrum to achieve the purpose of removing impurity peaks.The experimental spectrum of Ag target and the operation of Al target are smoothed when the buckle spectrum is processed.This is because both the Ag target experimental spectrum and the Al target experimental spectrum have statistical fluctuations.If the spectrum is deducted directly will further increase the statistical fluctuation range in the spectrum line,the deducted spectrum line morphology will be more disordered.After the buckle spectrum is completed,the experimental spectrum of Ag target impacted by positrons with impurity peaks is smoothed by different methods,and the best smoothing scheme is selected to obtain the corresponding net counting of characteristic peaks.It can be seen that spectrum smoothing technology plays an important role in the data processing of such experimental spectrum,effectively reducing the true spectrum line shape,and not introducing new impurities too much.For the experimental spectrum of 6-9keV positron impact Pb target,because it is relatively influenced by statistical fluctuations,it is difficult to select the boundary of characteristic peak,and it is difficult to distinguish weak peak,so the reading of net counts of characteristic peak directly is not accurately.Smoothing the X-ray spectrum can not only reduce the influence of the spectrum line on the statistical fluctuations and noises,but also make the profile of the spectrum clear,the weak peaks can be displayed,and the reading of the net count of the characteristic peak is convenient and the accuracy is improved.The introduction of spectrum smoothing technology in the analysis of X-ray spectrum impacted by positron not only improves the processing efficiency,but also reduces the impact of the contingency in data reading caused by fluctuations,which provides great convenience for obtaining accurate characteristic peak net counts.There are many kinds of smoothing methods,so it is necessary to adjust to a more suitable smoothing method according to the actual situation of experimental spectrum to obtain better smoothing effect.According to the analysis of the results of the current processing,the method of gravity center and least square has a better smoothing effect for the energy spectrum with less influence on the statistical fluctuations.For the energy spectrum affected by statistical fluctuations,the effect of Fourier transform method is relatively significant.Finally,according to the specific situation,the smoothness degree is adjusted to obtain the best smoothing effect.