Characterization of flour concentration and geometry in organic scintillators for in situ beta imaging
Development of a small area (1-2 cm2) 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 charge 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 flour ([0.5] to [2.0%] by weight), and varying thickness cylindrical configurations of the intended imaging detector. The new flour had an emission maximum increasing from 431 to 436 nm with increasing flour concentration. The decay time(s) had two components (0.38, 1.74 nsec). There was an approx.20% increase in light output with increasing flour concentration, measured with both 204Tl betas and conversion electrons from 207Bi. The highest light output of this new scintillator was measured to be approx.30% lower than BC404. Simulations predicted the 1.5 mm scintillator thickness at which light output and energy absorption for approx.700 keV electrons (e.g. from 204Tl, 18F) 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.
