Research On The Scintillation Mechanism And Pulse Shape Discrimination Of Inorganic Scintillators

The study of scintillation mechanism of inorganic scintillators is an important basic research,which not only helps to understand the characteristics of scintillators,but also guides the optimization of new scintillator materials and the development of new radiation detection methods.Lanthanum bromide?La Br₃:Ce?is one of the most representative novel inorganic scintillator materials in the past two decades.Its excellent material properties have been extensively studied and applied in nuclear physics and astrophysics experiments.In recent years,many research groups have studied the?/?pulse shape discrimination?PSD?in La Br₃:Ce crystals,but contradictory results were achieved.Such controversy proposed a more critical puzzle.La Br₃:Ce is considered to not possess different decay components,but has been proved to have the capability of discriminating gamma and alpha events using fast digitizers at room temperature.The physical mechanism of such PSD capability of La Br₃:Ce remains unclear.Further research on scintillation mechanisms based on La Br₃:Ce will also help to better understand the problems of quenching and nonlinearity of inorganic scintillator materials.Startting with the pulse shape discrimination of La Br₃:Ce detector,researches on the scintillation mechanism and PSD performance,including the readour electronics and PSD algorithm,are carried out in this work.Considering the scintillation mechanism,coupled rate and transport equations are established to explore the scintillation processes of La Br₃:Ce based on the the previous researches on the modelling of inorganic scintillators and related experimental measurements.With one parameter set,the model reproduces multiple observables of La Br₃:Ce scintillation responses,including the ionization density-dependent pulse shape differences for alpha or gamma particles,the proportionality response of electrons and quenching factor of alpha particles.In particular,the quenching process between the excited states of doped ions(Ce^3+*)are proposed and quantitatively calculated due to the higher doping concentration of La Br₃:Ce crystal,which has then been experimentally verified as well.Moreover,the model also provides insight on the best choice of 5%Ce concentration for La Br₃:Ce crystal growth and forecasts the generality of ionization density-dependent pulse shape differences in other novel and fast inorganic scintillators,such as LYSO and Ce Br₃.For the achievement of PSD performance of inorganic scintillators,the present study quantitatively,taking La Br₃:Ce as an example,analysed the influence of digitiser properties in terms of fast amplifiers,sampling rate??,and vertical resolution on the spectral resolution and PSD performance.Furthermore,this analysis also provides a general rule about the optimal design of waveform digitisers for similar applications based on digital waveform processing.This work also designed and implemented an optimized digital La Br₃:Ce detector system to study the performance of PSD application.The charge comparison method?CCM?for alpha and gamma discrimination in La Br₃:Ce is quantitatively analysed and compared with two other typical PSD methods using digital pulse processing.The algorithm parameters and discrimination efficiency are calculated for each method.Moreover,for the CCM,the correlation between the CCM feature value distribution and the total charge?energy?is studied,and a fitting equation for the correlation is inferred and experimentally verified.Using the equations,an energy-dependent threshold can be chosen to optimize the discrimination efficiency.Additionally,the experimental results show a potential application in low-activity high-energy?measurement by suppressing the alpha background and improving the MDA.A self calibration and stablization method for spectral application,which utilizes the alpha background as calibration,is also proposed to improve the long-term peformance of the detector.