Properties of High-Energy X-Ray Detector With Heavy-Metal-Oxide Nanoparticle-Loaded Plastic Scintillator

A heavy-metal-oxide nanoparticle-loaded plastic scintillator (PLS) is effective for a fast detector to measure high-energy X-rays, with a count rate of
${>}10^{7}\,\,\text{s}^{-1}$
and sub-nanosecond time resolution. We polymerized up to 50-wt% Bi2O3 nanoparticle-loaded PLS (Bi-PLS) by mixing with 2-(4-tert-butylphenyl)-5-(4-biphenyl)-1,3,4-oxadiazole as fluorophore-based polystyrene or polyvinyltoluene. A 40-wt% Bi-PLS was evaluated with a high-speed photomultiplier tube (PMT). The pulse-height and time spectra were obtained using a synchrotron X-ray beam of the photon factory (PF) ring, with the detector at 73.04 keV. The detection efficiency reached 25.4 ± 0.1% for a thickness of 3 mm, and the time resolution [full-width at half-maximum (FWHM)] was 0.24 ± 0.06 ns. The counting rates were recorded at 57.61 keV in the multibunch mode of the PF ring, with a maximum count rate of 3.28
$\times \,\,10^{7}\,\,\text{s}^{-1}$
at an input photon rate of 1.99
$\times \,\,10^{8}\,\,\text{s}^{-1}$
. Another X-ray detector using 40-wt% HfO2 nanoparticle-loaded PLS (Hf-PLS) was operated around the Hf
$K$
absorption edge of 65.35 keV to investigate the effects of
$K$
X-ray emission. The emitted
$K$
X-rays from the Hf-PLS reduced the detection efficiency to a value less than that calculated with photoelectric absorption. Furthermore, it affected the time spectrum by adding a slight peak tail due to the
$K$
X-ray escape events. However, with a suitable setting for the threshold level of the pulse height, the detector was confirmed to exhibit superior performance in the time spectrum even over the high-
$Z$
atom’s
$K$
absorption edge.