| General neutron fields are accompanied by gamma rays,in the military,energy,medical fields,radiation monitoring,neutron spectrum analysis,radiation imaging and other related technology applications need to screen neutron and gamma signals.Lithium base elpasolite scintillation crystals not only have excellentγenergy resolution,high light output,but also excellent neutron/γdiscrimination ability,which makes this kind of crystals have a broad application prospect.At present,the growth,preparation and application technology of such crystals are not mature enough,and the domestic high-quality crystals still rely on imports.In this paper,the crystal growth and packaging technology of Cs2Li La Br6（CLLB）crystal with the highest light output and the highest resolution were studied,and the crystal characteristics and scintillation performance of the crystal were analyzed by various testing methods.After the stable growth process was obtained,the doped crystal growth was carried out and the properties were compared.Research on screening methods and dose monitoring was carried out,and a dual read neutron/γmixed field dose measuring test device was developed based on Cs2Li YCl6（CLYC）crystal with the best screening performance.In view of the response ability of Cl-containing elpasolite scintillators from thermal neutron to fast neutron energy range,the neutron energy spectrum measurement technique has been studied.The main research contents,methods and related results are as follows:（1）A three-temperature crucible descending furnace was built to study the growth and packaging technology of CLLB and its doped crystals.The technological process,temperature field design and formula design in crystal growth process were studied.The temperature gradient of the two growth furnishes is 1.8℃/mm and 2.0℃/mm respectively,the crucible descent rate is 0.3 mm/h,and the Li Br excess is 100%,and the crystal with equal diameter part of 1 inch diameter is successfully grown.1%Ce element doping can obtain the ideal effect in terms of resolution and light output.（2）The crystallographic properties of conventional CLLB:Ce crystals and doped CLLB crystals were analyzed by material characterization.Scanning electron microscopy（SEM）and X-ray diffraction（XRD）demonstrate the successful growth and crystal deliquescent of the crystalline materials.Thermogravimetric differential scanning calorimetry（TG-DSC）shows that the melting point of the crystal is about 495℃,and the crystal contains eutectic impurities.Energy dispersive spectroscopy（EDS）and X-ray fluorescence spectroscopy（XRF）demonstrate the successful doping of target elements in several doped crystals.The emission spectra of all doped Ce crystals are basically the same,with peaks of 395 nm and 420 nm.The emission peak of undoped Ce crystals appears blue shift due to the dominant intrinsic luminescence mechanism.The non-Ce doped crystal still has a small emission peak at about420 nm,which is inferred to be related to the difficulties in the purification of lanthanide raw materials.（3）Scintillation properties of the grown CLLB:Ce,CLLB:Ce,Y,CLLB:Y,intrinsic CLLB,CLLB:Ce,Mg,CLLB:Ce,Ca,CLLB:Ce,Sr were analyzed.Firstly,a set of performance testing and analysis methods based on digital signal sampling is established.The results indicate that the optimal energy resolution of the 1-inch CLLB:Ce crystals is 3.9%,with a maximum output of 48432 Photons/Me V@0.662 Me V.The fast and slow decay times of 1%Ce doped CLLB crystals are 190 ns and 1080 ns,respectively,and the discrimination figure of merit（FOM）of charge comparison method is 1.27.The neutron andγsignal have the time resolution of 1.46ns and 1.76 ns signal with CR173-01 PMT broadened,respectively.The scintilation performance and neutron/γdiscriminability of the CLLB crystals doped only Y（1%）are similar with the intrinsic CLLB crystals,with the output of approximately 26000 Photons/Me V with the energy resolution ranging from 5.0%to 6.0%@0.662 Me V.Compared with CLLB:Ce crystal,FOM reaches 1.6～1.8,which is due to the large difference in the slow decay time of neutron signal andγsignal.In bivalent cationic codoped crystals,Ca doping results in crystal transparency and scintillation performance decrease.1%Mg and Sr doping has no obvious effect on energy resolution and optical output,but the discrimination ability of Mg doped crystal is inferior to CLLB:Ce crystal.Two crystals were cut and packaged in the equal diameter part of the CLLB:Ce,Sr ingot.The crystal near the lower end has better energy resolution and discrimination performance than the crystal at the upper end.（4）The neutron/γscreening method was studied,and the mixed radiation field dose monitoring test device was designed and developed.k-means clustering with vector projection method can achieve real-time screening and has similar performance to charge comparison method in resisting low sampling depth.Because it is sensitive to vector dimension,it is inferior to charge comparison method in resisting low sampling rate.Both XGBoost and Light GBM machine learning algorithms have 100%accuracy,no matter the sampling rate is reduced to12.5 MS/s or the sampling depth is reduced to 4 Bit.In frequency domain gradient method,frequency domain accumulation method and wavelet transform scale function maximum method,frequency domain accumulation method has the best discrimination performance,which is similar to vector projection method and charge comparison method.Aiming at the problem of over-response ofγenergy response in low energy region,the accuracy of hardware correction method and software correction method based on full spectrum was studied by Monte Carlo simulation.In hardware correction,the correction effect of W and Pb is better than Sn,and the fluctuation error of energy response of CLLB and CLYC is within30%in the energy range of more than 200 ke V.By software correction method,γspectrum is divided into 100 ke V for each segment,and the fluctuation error of energy response within the energy range of more than 50 ke V can be achieved within 30%.CLYC dose measuring test device based on hardware correction and charge comparison method was designed with a FOM of 1.89,which was verified and calibrated in a variety ofγfields,Pu-Be and Am-Be neutron fields.（5）The neutron spectrum measurement technique based on elpasolite scintillation detector is studied.In view of the nonlinear characteristics of optical output in neutron measurement,a nonlinear optical output scale function combining Payne/Onsager model and Bethe formula is proposed,and a better fitting effect is obtained in the high energy region.Using 252Cf continuous neutron as the research object,the performance of nine kinds of energy spectrum inversion methods is calculated and analyzed by the method of forward modeling before inversion.With root mean square error（RMSE）as the evaluation basis,compared with non-negative least squares（NNLS）,Tikhonov regularization,truncated singular value decomposition（TSVD）,Gold,Gravel,Lucy-Richardson（L-R）,maximum a posterior probability（MAP）,particle swarm optimization（PSO）and genetic algorithm（GA）,Gold algorithm has the best performance and stability with the reduction of the signal-to-noise ratio. |
