Characterization of fluor concentration and geometry in organic scintillators for in situ beta imaging

Abstract

Development of a small area (1-2 cm/sup 2/) in situ beta imaging device includes optimization of the front end scintillation detector, which is fiber optically coupled to a remote photon detector. Thin plastic scintillation detectors, which are sensitive to charged particles, are the ideal detectors due to the low sensitivity to ambient gamma backgrounds. The light output of a new binary plastic scintillator was investigated with respect to increasing concentrations of the fluor (0.5-2.0% by weight) and varying thickness cylindrical configurations of the intended imaging detector. The fluor had an emission maximum increasing from 431 to 436 nm with increasing fluor concentration. The decay time(s) had two components (0.38 and 1.74 ns). There was an /spl sim/20% increase in light output with increasing fluor concentration, measured with both /sup 204/Tl betas and conversion electrons from /sup 207/Bi. The highest light output of this new scintillator was measured to be /spl sim/30% lower than BC404. Simulations predicted the 1.5 mm scintillator thickness at which light output and energy absorption for /spl sim/700 keV electrons (e.g., from /sup 204/Tl, /sup 18/F) were maximized, which corresponded with measurements. As beta continua are relatively featureless, energy calibration for the thin scintillators was investigated using Landau distributions, which appear as distinct peaks in the spectra. As the scintillators were made thinner, gamma backgrounds were shown to linearly decrease.