CHARACTERIZATION OF FLUOR CONCENTRATION AND GEOMETRY IN ORGANIC SCINTILLATORS FOR IN SITU BETA IMAGI - Nuclear Science Symposium and Medical Imaging Conference Record, 1995., 1995 IEEE

Gamma transparent materials are necessary to avoid detection 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 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 ( [ O S % ] to [2.0%] by weight), and varying thickness cylindrical configurations of the intended imaging detector. The new fluor had an emission maximum increasing from 431 to 436 nm with increasing fluor concentration. The decay time(s) had two components (0.38, 1.74 nsec). There was an -20% increase in light out ut with increasing fluor concentration, measured with both P04Tl betas and conversion electrons from '07Bi. The highest light output of this new scintillator was measured to be -30% lower than BC404. Simulations predicted the 1.5 mm scintillator thickness at which light output and energy absorption for -700 keV electrons (e.g. from '04Tl, '*F) were maximized, which corresponded with measurements. As beta continua are relatively featureless, energy calibration for the thin scintillators was investigated and consequent image misposition due to ambient gamma backgrounds (e.g. annihilation photons from '*F positrons). The success of the imaging device depends on detecting a sufficient number of optical photons at the photodetector end [6] with which energy and positioning information combine to form images of the beta distributions. A high photon yield plastic scintillation detector which is sensitive to charged particles (p) of <1 MeV would be the ideal detector due to its low Z (6.6) and density (1.05 g/cm3), hence low sensitivity to ambient gamma backgrounds. Organic scintillators have a known variation in light output and decay time as a function of fluor (dopant) concentration [7,8]. Additionally, optimization of scintillator geometry is an important aspect of maximizing pulse height, especially when guiding light into and through fiber optics [ 1-51. In this work a new binary fluor (from Bicron) prepared in various concentrations ([0.5%] [2.0%] by weight) in a polyvinyltoluene (PVT) solvent matrix was evaluated in comparison to commercially available BC404 (Bicron) to determine its suitability for use in the beta imaging probe. Various geometrical conditions necessary for optimal light output and device operation were also investigated by simulations and measurements. -using Landau distributions, which appear as distinct peaks in the spectra. As the scintillators were made thinner, gamma backgrounds were shown to linearly decrease.