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6Li-Doped plastic scintillators (PSs) have been optimized as radioluminescent sensors for detection of fast/thermal neutrons and gamma rays for several purposes such as homeland security. Among 16 low molecular weight (C < 8) lithium carboxylates, Liα-valerate (LiαVal) exhibits high potential for loading (up to 50 wt%) in clear PSs composed of polystyrene and standard fluors (20 wt% PPO, 0.03 wt% POPOP). A methodical study of PS composition illustrates that the Li carboxylates and methacrylic acid comonomers impact the scintillation yields (from 4410 to 7790 ph per MeV) and nthermal/nfast/gamma discrimination performances with significant figures of merit (from 0.23 to 1.45 above 180 keVee).

We report herein the synthesis of a new series of plastic scintillators (PSs) loaded with 6Li210B4O7 nanoparticles (NPs), as new radioluminescent sensors for fast/thermal neutron and gamma ray detection in the critical context of homeland security. This study aims to evaluate the benefit of such nanoparticles towards thermal neutron detection in a fast neutrons/gamma discriminating PS composition. First, a size-controlled synthesis of Li2B4O7 NPs assited with poly(N-vinylpyrrolidone) (PVP) is performed. Then enriched 6Li210B4O7 NPs (65 ± 22 nm) are dispersed in clear PSs mainly composed of polystyrene and standard fluorophores (20 wt% PPO, 0.03 wt% POPOP). For the first time, a triple nthermal/nfast/gamma discrimination is presented with a NP-loaded plastic scintillator, where both 6Li(n,α) and 10B(n,α) are observed.

International audience; Since Helium-3 shortage announcement, organic scintillators play a major role in neutron detection. Our laboratory decided to focus on plastic scintillators and their ability to discriminate fast neutrons from gamma rays. In this work, we highlight the influence of the secondary fluorophore in lab-made plastic scintillators. The secondary fluorophore is generally added in the scintillating mixture to shift the emission wavelength towards the transparency domain of the material to improve its attenuation length. Thus, it is considered as a harmless molecule and is barely seen as a key criterion that could enhance the performances of the organic scintillator. In our work, we demonstrate that this molecule, even added at a small concentration (typically in the range 0.02–0.2 wt%), directly impacts the neutron/gamma discrimination ability of plastics. Not only the secondary fluorophore plays a role in self-absorption of the scintillating material, but also the couple it creates with the primary fluorophore has to be carefully chosen, as some specific triplet energy transfers between the two fluorophores can influence the neutron/gamma discrimination abilities of the plastic scintillator. Aside from classical photophysical inconveniences such as self-absorption or diffusion, the possibility that the whole, bulk material was heterogeneous in a photochemical point of view was also checked. Thus, various samples were cut from bulk monoliths and their pulse shape discrimination compared with the parent scintillator in terms of Figure of Merit and light output.

We report herein the application of a new series of plastic scintillators loaded with lithium tetraborate nanoparticles (Li 2 B 4 O 7 ) designed for the simultaneous detection of fast neutrons, thermal neutrons and gamma-rays. First, MCNP simulations are performed to highlight the potential benefit of Li 2 B 4 O 7 loading. Then, a nanoparticle-loaded scintillator is prepared and evaluated towards the detection of a partially thermalized neutron/gamma 252-californium source. Several scenarios of radiation/matter interactions are evaluated against the observed results. A detection chamber composed of boron-containing chipboard wood has been specifically designed and a subtraction method was set up to afford the best discrimination pattern. For the first time, a triple discrimination is presented with a nanoparticles-loaded plastic scintillator, where both 6 Li(n, α ) and 10 B(n, α ) signatures are observed. A Figure of Merit of 1.40 was calculated between fast neutrons and gamma rays around 480 keVee. The Figure of Merit between fast + thermal neutrons and gamma rays is slightly worse as it is 1.16 at 380 keVee.