X-rays Cure Snow Globe of “Static Cling”

March 16, 2008

Snow globe and x-ray machineClick here to watch the demo (1:40, AVI format, 4 MB). The forced-air snow globe has become a popular piece of holiday decor in recent years. But, as the Wikipedia article mentions, this toy is menaced by static cling: “snow” adheres to the inside of the plastic globe and refuses to fall. (Presumably, the globe and the snow become triboelectrically charged during operation.) So how do you instantly exorcise this static cling from your snow globe? Simple. You expose your snow globe to a powerful beam of ionizing radiation.

The video available here depicts a snow globe suffering from extreme static cling being treated with an 80 kVp / 3 mA portable x-ray machine that produces about 300 R / hr near the midpoint of the globe. The x-rays create ions in the air that rapidly discharge the plastic “snow” and globe, eliminating the electrostatic forces trapping the snow against the globe. This is a variant on the radiation-discharging-electroscope demo commonly practiced in physics lectures in the early part of the 20th century. A good example can be found in Sutton RM, ed., Demonstration Experiments in Physics, New York: McGraw-Hill (1938.):

“Three rubber balloons filled with hydrogen or illuminating gas and attached to a common point on the table by silk threads make an effective large-scale electroscope. When charged, they will stand far apart but will come together promptly when an x-ray beam is turned on them.” (p. 497-498.)

This genre of demonstration is rarely performed today for safety and liability reasons. In 1938, folks were aware that radiation had its hazards but were pretty casual about controlling exposure. Sutton’s words of caution prefacing the above excerpt embody this attitude perfectly:

Caution: Prolonged exposure to x-rays may produce bad burns. Do not expose any part of the body for more than a few minutes.”

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