Paper Scintillator Incorporated with Scintillator-Silica Fine Powders: Photophysical Characterization and Proof of Concept Demonstration of Tritium Detection.

In order to decrease the generation of radioactive waste, it is of interest to develop a scintillator capable of absorbing tritiated solutions for efficient detection of low-energy ß-particles from tritium. In this work, paper scintillator incorporated with scintillator-silica fine powders (FPs), which is composed of scintillator-silica nanoparticles (NPs) attached to silica FP, was fabricated and evaluated. The scintillator-silica NPs contained liquid scintillators benzoic acid, 2,5-diphenyloxazole (PPO), and 1,4-bis(5-phenyloxazol-2-yl) benzene (POPOP). Photophysical characterization was executed by means of photoluminescence, fluorescence lifetime, quantum efficiency, and radioluminescence under X-ray excitation. POPOP emission was confirmed by absorbing the emissions from benzoic acid and PPO. Radioluminescence results confirmed POPOP emission. Fluorescence lifetime analysis yielded a 1.29 ± 0.01 ns main fast decay (64.2%) combined with a 4.00 ± 0.04 ns slower decay (35.8%). The combined luminescence results suggested that most POPOP in the paper scintillator was solvated. At 301 nm, the average quantum efficiency from both faces of the paper scintillator was about 4%, and at 370 nm, it was about 11%. The paper scintillator detected 3H ß-particles by dipping the paper scintillator into tritiated water without a liquid scintillator. The counting efficiency depended on water content in the paper scintillator, and it increased to above 10% for tritium activity less than 200 dpm since it was preferentially adsorbed by vapor pressure isotopic effect and isotopic exchanged tritium on the surface of the scintillator-silica FP in the paper scintillator.

Microgravity effects on nonequilibrium melt processing of neodymium titanate: thermophysical properties, atomic structure, glass formation and crystallization.

The relationships between materials processing and structure can vary between terrestrial and reduced gravity environments. As one case study, we compare the nonequilibrium melt processing of a rare-earth titanate, nominally 83TiO2-17Nd2O3, and the structure of its glassy and crystalline products. Density and thermal expansion for the liquid, supercooled liquid, and glass are measured over 300-1850 °C using the Electrostatic Levitation Furnace (ELF) in microgravity, and two replicate density measurements were reproducible to within 0.4%. Cooling rates in ELF are 40-110 °C s-1 lower than those in a terrestrial aerodynamic levitator due to the absence of forced convection. X-ray/neutron total scattering and Raman spectroscopy indicate that glasses processed on Earth and in microgravity exhibit similar atomic structures, with only subtle differences that are consistent with compositional variations of ~2 mol. % Nd2O3. The glass atomic network contains a mixture of corner- and edge-sharing Ti-O polyhedra, and the fraction of edge-sharing arrangements decreases with increasing Nd2O3 content. X-ray tomography and electron microscopy of crystalline products reveal substantial differences in microstructure, grain size, and crystalline phases, which arise from differences in the melt processes.