Exploratory Research on the Development of Novel ${\rm Ce}^{3+}$ -Activated Phosphate Glass Scintillators

We report the discovery of a new family of Ce³⁺-activated phosphate glass scintillators that can be formed either with or without the addition of ⁶Li, for neutron or X-ray/gamma-ray radiation detection, respectively. Trivalent cerium can be efficiently introduced into these phosphate glasses in surprisingly high concentrations in the form of anhydrous cerium tri-chloride. Additionally, these glasses can be melted and poured at the relatively low temperatures of 1000-1050degC (i.e., substantially lower than silicate glasses), and to retain the cerium in the trivalent state it is not necessary to maintain highly reducing conditions during the synthesis process. The family of alkaline-earth-alkali phosphate glasses investigated here represents a system with two dissimilar cations - thereby offering a large range of potential compositional variations, substitutions, and combinations. In order to alter the scintillator characteristics, we have explored part of that compositional space by studying Ca-Na, Ca-Li, Ca-Cs, Ca-Rb, Ca-K and Ca-Ba-Na phosphate glasses, as well as various co-doping and post-synthesis thermal processing schemes. A series of experiments under X-ray, gamma-ray, and neutron excitations was carried out. The broad, peaking at about 354 nm, UV scintillation of these glasses is well suited for applications that use common photomultipliers with bi-alkali photo-cathodes. Pulse shape measurements show that the primary component of the scintillation in most of these glasses corresponds to 75-90% of the emitted photons, and it decays with a time constant of 30 to 40 ns, which classifies these materials as reasonably fast scintillators. Although the gamma-induced light yield of these new scintillating phosphate glasses is, thus far, only about 30% of that of commercial GS20 silicate glass, due to the generally faster scintillation, the initial amplitude of the scintillation pulse of these glasses is close to that of the above-mentioned GS2- - 0 scintillator.