1. Field of the Invention
The present invention relates to a scintillator. The invention can be applied to the field of radiation measurement, radiation non-destructive inspection, radiation medical diagnosis, etc.
2. Description of the Related Art
A scintillation counter is known as a detector for detecting radiation such as γ-rays or X-rays. The scintillation counter has a scintillator. When an electron state in the scintillator is excited by radiation, fluorescence is emitted while the electron state is restored to a ground state. The fluorescence is detected so that the amount of radiation applied on the scintillator is detected.
Accordingly, the characteristics required of the scintillator are (1) high quantum efficiency in an irradiation state, (2) short life of fluorescence, etc.
From the point of view of facilitation of production of crystal, scintillation efficiency, etc., ionic crystal of alkali halide or the like is used as the scintillator. In practice, NaI:Tl or CsI:Tl containing alkali halide such as NaI or CsI, and a fluorescence activator such as Tl added to the alkali halide is generally widely used.
Although the ionic crystal of NaI or CsI has a merit in facilitation of production of crystal, high scintillation efficiency, etc., there is a chemical stability problem that the ionic crystal deliquesces by absorbing water. In addition, because Tl added as a fluorescence activator is a highly toxic substance, there is also a problem that Tl has bad influence on the human body and the environment.