Preparation and characterization of thermal neutron sensitive lithium doped polystyrene plastic scintillators

Abstract [Background] Lithium-doped plastic scintillators possess the dual-mode detection capability for both fast and thermal neutrons, and combine the advantages of conventional plastic scintillators such as cost-effectiveness and the ability to fabricate in large sizes, have drawn much attention and shown great potential for thermal neutron detection in recent years. [Purpose] This study reports on the preparation and performance characterization of polystyrene (PS) plastic scintillators doped with lithium methacrylate (LiME). [Methods]Through investigating the correlation between the radioluminescence intensity and the concentrations of the initiator 2,2'-Azobis(2-methylpropionitrile) (AIBN), primary fluorescent dye 2,5-Diphenyloxazole (PPO), and the wavelength shifter 1,4-Bis(5-phenyl-2-oxazolyl) benzene (POPOP) in the scintillator matrix, the optimal mass concentrations were determined experimentally to be 0.1% for AIBN, 2% for PPO, and 0.02% for POPOP. Utilizing a thermal polymerization method, a series of plastic scintillator samples with a diameter of 33 mm and a thickness of 6 mm, doped with LiME at mass concentrations ranging from 0 to 12 %, were successfully prepared. The optical transmittance (OT), photoluminescence (PL), radioluminescence (RL), and pulse height spectrum (PHS) of these samples were characterized. [Results] The results indicate that the lithium-doped plastic scintillators exhibit excellent optical quality, with the emission spectrum's peak position remaining consistent with that of the pure plastic scintillator. However, the fluorescence intensity and light output of scintillator decreases with increasing LiME content, which is presumed to be associated with fluorescence quenching effects resulting from the doping process. [Conclusions] Large lithium-doped plastic scintillators with high optical quality were successfully prepared. Though the performance is yet to be improved, these scintillators are promising for applications requiring efficient dual-mode detection of fast and thermal neutrons.