Study On The Particle Identification Ability Of CsI（Tl） Scintillation Detector In The Medium Energy ⁶He+²⁰⁸Pb Experiment

The charge integration method is one of the most used technique to identify the particle for the scintillation detector such as Cs I（Tl）,and the particle identification ability is affected by the selection of delay and width of the integration gate.Usually,electronic hardware methods were used to integrate the fast and slow components of the pulse shape in experiments to identify the type of particles.It will increase the time of electrical tuning in experiment because the integral gate could not be changed once it is selected.With the development of digital acquisition systems,complete pulse shape information that can be acquired during experiments and analyzed offline by selecting the best integral condition,overcoming the weakness of hardware integration.In the⁶He+²⁰⁸Pb reaction experiment carried out at the Lanzhou radioactive beam line with intermediate energy,the full information of pulse shape for each Cs I（Tl）was recorded using the XIA acquisition system.Then,the study of searching the best condition of integral gate for the best particle identification have been done.The offline data analysis is done with ROOT software.The fast and slow component charge integration gates can be set on the pulse waveform,and the corresponding charge amount can be obtained by integration,and the two-dimensional spectrum is made.In the two-dimensional spectrum,different charged particles are distributed on different curves.The known particle ⁶He and tritium（t）in the radioactive ion beams are taken as the standard particles to judge the particle identification ability by changing the width and position of the integration gate.The best identification result corresponds to the best separation of these two particles in the 2-dimension identification spectrum.Setting a straight-line Ax+By+C=0 along the ⁶He distribution（A and B cannot be zero at the same time）and selecting t and part ⁶He in the box in the 2-dimension identification spectrum,the distance from the particles in the selected area to the straight line are calculated using the distance formula from a point to the line.The one-dimensional spectrum of particle distance distribution is obtained,and the center value of the two peaks and the parameters characterizing the width of the peak are obtained by Gaussian fitting for t and ⁶He.Here we introduce a quality factor Fo M（Figure of Merit）from a reference,which is calculated by the parameters obtained by Gaussian fitting,to characterize the particle identification ability.The particle identification ability is compared by comparing the value of Fo M.The greater the Fo M value,the better the identification ability.In the article,the optimal integration interval conditions for particle identification performance of detection units Cs I28,Cs I21,and Cs I29 with a large number of particle types were studied,and the selection range of the starting and ending points of the charge integration gates for fast and slow components on three detection units was determined.Because the voltage applied to different detection units during the experiment is different,particles with the same energy have different amplitudes of pulse waveforms on different detection units.On Cs I28,selecting the integration interval Slow gate:-20ns～+150ns,Tail gate:+300ns～+1800ns.For Cs I21 and Cs I29,changing the starting and ending points of the integration gate based on the ratio of the amplitude of the pulse waveform to Cs I28,with the peak of the pulse waveform as the center.The obtained integration interval falls precisely within the calculated optimal range.By discussing the results of the best discrimination intervals of the detection units Cs I28,Cs I21 and Cs I29 which is shown that it is a reliable method to determine the position of the integration gate according to the proportion of the pulse amplitude on different detection units.