Bi2O3 Nanoparticle-Loaded Plastic Scintillator for High-Energy X-Ray Detection

Abstract

In this study, we successfully fabricated a Bi <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O3 nanoparticle-loaded plastic scintillator (PLS) with high detection efficiency for high-energy X-rays. Such a heavy-metal-oxide-loaded PLS is useful for the measurement of high-energy X-rays with a high count-rate >10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sup> s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> . Bi <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O3 nanoparticles were synthesized by surface modification with aliphatic carboxylic acid from a triphenylbismuthine starting material. Up to 50 wt% surface-modified Bi <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O3 nanoparticle-loaded plastic scintillator (50 wt% Bi-PLS, 31 ± 1 wt% bismuth in the plastic) successfully maintained transparency after polymerization by mixing monomers consisting mainly of styrene or vinyltoluene and 2-(4-tert-butylphenyl)-5-(4-biphenylyl)-1,3,4-oxadiazole as the fluorophore. The Bi content of the Bi-PLSs was greater than that of PLSs using organobismuth compounds. The optical properties of each Bi-PLS (8 mm diameter and 3 mm thickness) were measured for transmittance, photoluminescence, and quantum yield. The average transmittance between 380 and 780 nm was over 70% (except for 50 wt% Bi-PLS) and was sufficiently high for practical use. In the recorded photoluminescence spectra, the peak attributed to fluorophore emission was clearly observed at 386 nm, even for 50 wt% Bi-PLS. We tested the Bi-PLS mounted on a photomultiplier tube using a synchrotron X-ray beam (67.41 keV at beamline BL-14A of the Photon Factory). The detection efficiency of 50 wt% Bi-PLS reached 36.8 ± 0.5%, 5.0 times higher than that of a commercially available 5 wt% Pb-loaded PLS. A superior time resolution (full width at half maximum) of 0.21 ± 0.06 ns was obtained using 20 wt% Bi-PLS.