Evaluation of wavelength shifters for spectral separation of barium fluoride emissions.

Abstract

Application of the barium fluoride (BaF$\sb2$) scintillator for characterization of intense radiation fields has been pursued since the fast component was discovered in the early 1980's. Unfortunately, $\approx$80% of its emissions have a slow $\approx$600 ns scintillation decay time. The long decay time hampers the use of this scintillator at high count rates because the slow emissions appears as afterglow and have an intensity that varies with the interaction rate in the crystal. This dissertation examines the possibility of temporally separating the BaF$\sb2$ emissions by spectrally separating them using wavelength shifting techniques. Three wavelength shifting techniques are presented: orthogonal geometry, in-line: solute excitation, and in-line: solvent excitation. The latter technique shows the greatest potential for spectral separation while delivering the highest efficiency. Unfortunately, wavelength shifting techniques are not sufficient in and of themselves to suppress the slow emissions to the desired degree. However, wavelength shifting can be used in conjunction with other technologies to further decrease the response of the system to the slow BaF$\sb2$ emissions. Discussions of the three techniques as well as the physical limitations imposed by wavelength shifters are presented along with a novel temporal technique to measure the fluor quantum efficiency in solution.