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09 February 2012

Answer to Question #6719 Submitted to "Ask the Experts"

Category: Industrial Radiation — Industrial Applications

The following question was answered by an expert in the appropriate field:

Several articles, including a fact sheet from the Centers for Disease Control and Prevention, state that cesium powder may glow. A reference to the Goiânia, Brazil, describes the material as glowing blue. Is this the Cerenkov effect to the air molecules or was a phosphor added to the cesium chloride to make it glow like the bad smell that is added to natural gas as a warning of a leak? I thought that radioactive material itself glowing was a myth.

The "cesium powder" in high-activity ¹³⁷Cs sources is cesium chloride, which is used to give the source a high-specific activity (activity per gram). Nonradioactive cesium chloride is a commonly used material in fluorescent screens used for making x-ray images. Thus, the cesium powder will glow or fluoresce when stimulated by self-absorption of its own beta- and gamma-radiation emissions. The reference to radioactive material glowing has to do with the early use of radium, mixed with a phosphorescent material, to paint clock and watch dials and hands.

John P. Hageman, CHP

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