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

In this study, we successfully fabricated a bismuth oxide (Bi2O3) 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 $10^{7}~\text{s}^{-1}$ . Bi2O3 nanoparticles were synthesized by surface modification with aliphatic carboxylic acid from a triphenylbismuthine starting material. Up to 50 wt% surface-modified Bi2O3 nanoparticle-loaded PLS (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 (PL), 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 PL 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 (PMT) using a synchrotron X-ray beam [67.41 keV at beamline BL-14A of the photon factory (PF)]. 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.