| 摘要 |
PURPOSE:To improve a starting characteristic and prevent a drop in a light flux during a life by forming a holding body of at least one kind of silica and alumina of 10-50% (mol%) and forming the rest of an oxide of a rare earth metal. CONSTITUTION:A holding body 18 dispersedly enclosing an radioactive material 20 is further enclosed in a luminous tube 4 where at least a rare earth metal is enclosed as a luminous metal for composing a holding body of at least one kind of silica and alumina 10-50% (weight%) and the rest of an oxide of a rare earth metal. Thereby, a reaction amount of a component of the holding body 18 and a rare earth metal halide is reduced and excessive reduction of an effective amount of the rare earth metal, which is the luminous metal, is suppressed, moreover dispersion of the holding body and the radioactive material 20 dispersedly contained in the tube wall of the luminous tube 4 is reduced thus sharply improve a light flux drop during a life as well as to improve a starting characteristic.
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