Preparation And Property Study Of A Novel Gadolinium Doped Liquid Scintillator

In recent years,neutron and neutrino detection has become a hot research topic in the world.The accurate and reliable detection of neutrino mixing angle?13 plays an important role in evidencing CP violation law and the existence of antimatter.At present,the main method to detect the neutron and neutrino is to adopt scintillation detector.As a core component of scintillation detector,compared with plastic scintillator and scintillation crystal,liquid scintillator has been paid more and more attention because of its advantages such as high light yield,good light transmission,easy preparation of large volume materials,and the unrestricted shape.The ideal liquid scintillator should have high light yield,large attenuation length,fast fluorescence decay time,low chemical activity and good safety.As the main component of liquid scintillator,solvent has a great influence on the performance of liquid scintillator.At present,many countries around the world have invested a lot of money to study the formula of liquid scintillator solvent to improve the overall performance of liquid scintillator.However,for a single solvent,there always exists some flaws and shortcomings,such as the low light yield,poor light transmission,and the bad compatibility with acrylic material vessel.When the second solvent are added to solve these problems,new problems will arise.Therefore,how to prepare the liquid scintillator with good comprehensive performance has been a difficult problem.In addition,compared with the hydrogen core of the liquid scintillator solvent,the rare earth metal gadolinium has a very large capture cross section for the neutron,so it is often added to the liquid scintillator to improve the detection efficiency of the neutrino.In this paper,the mixed solvent of PC-LAB was used as the matrix of liquid scintillator for the first time,and the advantages and disadvantages of the two solvents were combined to optimize the overall performance of liquid scintillator.The optimum proportion of mixed solvent was studied.Based on the light yield,attenuation length and chemical activity,it was found that the mixed solvent of 20% PC-80% LAB achieved better results.The PPO and bis-MSB were successively chosen as the primary fluor and wavelength shifter.The optimal formula of liquid scintillator was explored,and the properties such as the light yield,attenuation length,decay time and compatibility with acrylic materials were characterized.On the basis of this work,two methods,namely direct dissolution method and solvent extraction method,were used to prepare the Gd doped liquid scintillators,and the performances of the samples by two different methods was compared.It is well known that the light yield is a very important performance of liquid scintillator.The higher the light yield,the higher the energy resolution of liquid scintillator detector.In order to further improve the light yield of the liquid scintillator,bis-4-MOSB,which was a novel wavelength shifter,was designed and synthesized in this paper.The optical properties comparison with bis-MSB,which is the traditional wavelength shifter,were conducted.It was found that the novel wavelength shifter had higher light yield.In order to study the charge excitation characteristics of bis-4-MOSB and bis-MSB in the process of the luminescence,the theoretical calculation was also carried out by means of density functional theory(DFT).Based on the UV absorption and fluorescence emission,the appropriate calculation method was selected to calculate the frontier molecular orbitals energy bandgap.The frontier orbital composition of the methoxy and methyl in novel waveshifter and bis-MSB were analyzed by the natural atomic orbital method of Multiwfn 3.3.5.