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Radioactivity in cathode ray tubes

Kirner, Nancy P.; Troyer, G. L.; Jones, R. A.; Gray, E. W. Jr.

Operational Topic

While surveying used computer equipment out of a zone posted as a Contamination Area, 100% of the computer monitors surveyed had levels of radioactivity that were significantly above background. The radioactivity was primarily on the front face of the cathode ray tube and was not amenable to decontamination. Hot spots were found also along the edges and seals of the cathode ray tube. Similar surveys of computer monitors that were never in Contamination Areas confirmed that radioactivity was incorporated into the monitor. Surveys were made of recently manufactured television sets with similar results. Gamma spectroscopy indicates that the radioactivity is due to naturally occurring radioactive materials. Since most surveys of cathode ray tubes in the literature were made while the units were energized and indicated low-energy x-rays, the use of naturally occurring radioactive materials in the manufacture of cathode ray tubes has not been widely recognized. This paper presents the results of these surveys, the results of gamma spectroscopy, and a method for releasing existing computer equipment having naturally occurring radioactive materials.

A discussion of the natural radioactivity in CRT monitors and a method for evaluating them are presented so appropriate disposal decisions can be made.

* Kirner Consulting, Inc., Tacoma, WA; † Hanford Group, Inc., Richland, WA.

‡ Disposal of CRTs that do not have the potential for contamination or activation are typically not considered to be mixed waste even though they may contain very low-levels of naturally occurring radioactive material. When such “clean” CRTs are no longer useful they are recycled or, if waste, they are managed as dangerous waste, not mixed waste.

© 2004 by the Health Physics Society