Fast Scintillation X-Ray Detector Using Proportional-Mode Si-APD and a HfO2-Nanoparticle-Doped Plastic Scintillator

Abstract

We developed a new fast scintillation detector using proportional-mode silicon avalanche photodiode (Si-APD) for nuclear forward scattering experiments using high-energy synchrotron X-rays >30 keV. After a test of a prototype detector with a lead-loaded plastic scintillator (EJ-256, Eljen Technology) and proportional-mode Si-APD (S8664-3796(X), Hamamatsu Photonics) as a photodetector, we fabricated a four-channel detector using four $3\times 3\times 3$ mm3 EJ-256 scintillators and Si-APD arrays of $3\times 3$ mm2 pixels to increase the detection efficiency. The detector had a 12-mm beam path in the EJ-256. Moreover, a 10wt% HfO2-nanoparticle-doped plastic scintillator (Hf-PLS), 3 mm in diameter and 1 mm in thickness, was examined using the prototype detector. Hafnium is a heavy atom of atomic number 72 and the energy of the K-absorption edge is 65.351 keV. Its oxide nanoparticles, ~4 nm in diameter, were incorporated into a polymer matrix. The pulse-height distribution and time spectra for the detector with the Hf-PLS were measured at −34 °C with an APD gain of ~200 for 57.6-keV X-rays. The light yield of the Hf-PLS was 1.2 times that of the EJ-256 of the same size, and a good time resolution of 0.34 ns (full width of half maximum) was obtained better than that of 0.54 ns for the EJ-256. This was due to the difference in the scintillation solution, as only 2-(4-tert-butylphenyl)-5-(4-phenylphenyl)-1,3, 4-oxadiazole was added in the Hf-PLS, however, for in the EJ-256, the binary solutions, such as 2,5-diphenyloxazole and 1,4-bis (5-phenyl- 2-oxazolyl)benzene, were included.