Preparation And Properties Of Polystyrene-based Plastic Scintillator

Scintillator is a type of material,which can absorb radiant energy,convert partially absorbed radiant energy into light energy,and emit temporary fluorescence under the action of nuclear radiation(α,β,γ rays,etc.)or high-energy particles.As an important branch of the scintillator,the plastic scintillator is widely concerned because of its advantages of short decay time,high luminous efficiency,good physical property and chemical stability,easy transportation,non-toxicity,and low cost.Although the commonly used plastic scintillators have excellent comprehensive performance,one of drawbacks is that the detection efficiency of fast neutrons is low.The use of a plastic scintillator fiber with a core refractive index greater than the refractive index of the cladding make the fluorescence generated by neutrons and scintillators to be totally reflected,thereby improving spatial resolution and enhancing image contrast to improve detection of neutrons effectiveness.This thesis takes two steps to prepare plastic scintillator fibers.First,a non-initiator polystyrene-based plastic scintillator was prepared by thermal polymerization,and the relationship between its performance and the type and ratio of the first scintillation substance and the wave-receiver was investigated.The results show that the first scintillator and the wave-reducing agent are 2,5-diphenyl oxazole(PPO)and 1,4-bis(5-phenyl-2-oxazolyl)benzene(POPOP),respectively,and When the concentrations were 1 wt% and 0.02 wt%,respectively,the best luminous efficiency was achieved.Compared to the commercial plastic scintillator EJ-200 ‘s light yield was 83.49%,the photoproduction yield was 53.43% and the decay time was 1.8 ns.Subsequently,using the above optimal ratio,the first scintillator and the wave dissolving agent were dissolved in the styrene monomer.Using the method of pre-polymerization,heterotopy pressurization,end capping,step-program heating,unblocking and vacuum secondary curing,plastic scintillating fibers with different inner diameters(150 um,200 um,and 250 um)maintained at 7 cm were prepared.Another disadvantage of the commonly used plastic scintillators is the poor discrimination of low-energy neutrons.The solution is the introduction of 6Li with a large heat-trapping area in the plastic scintillatorIn this thesis,lithium methacrylate was first synthesized by acid-base neutralization reaction,and its structure was characterized by IR and NMR.It was then dissolved in methacrylic acid and the methacrylic acid solution was transferred to a solution of styrene in which the first scintillation substance and the wave-absorbing agent were dissolved.Finally,a lithium-doped plastic scintillator was prepared by thermal polymerization.The maximum lithium doping amount of the resulting scintillator is 0.89 wt%.With the increase doped lithium,the fluorescence performance of the scintillator is gradually decreasing.At the same time,compared to the EJ-200,the light yield of the largest lithium-doped scintillator is 72.3%,and the light yield relative to the germanium crystal is 46.27%.The decay time is 1.64 ns.