Glass Objects Bear Permanent Record, Scientist Reports : Simpler Method Found to Measure Radon Gas

Times Science Writer

An unusual new way to measure the concentration of radioactive radon gas in homes over long periods has been developed by a Swedish scientist.

Physicist Christer Samuelsson of the University of Lund in Sweden reported in a paper published in today's Nature magazine that glass objects such as windows, mirrors and the glass in picture frames contain a permanent record of the amount of radon that has been present in a house over its lifetime--or at least since the glass was brought into the home.

Radon in homes causes as many as 20,000 cases of lung cancer in the United States each year, second only to the number caused by smoking, according to the Environmental Protection Agency, and is the most common radioactive agent to which most people are exposed.

Could Prove Useful

Samuelsson's discovery could prove useful because measurement of radon levels is now a time-consuming process. The amount of radon that seeps into a house through cracks in the foundation, drains or other openings varies widely over the course of a year. It is thus necessary to leave a radon detector in the house for at least a year to get an accurate measurement of the average amount of radon present.

The new technique will allow researchers simply to remove a pane of glass and use it to determine the radon history of the house, a process that could be carried out in a few days.

U.S. scientists said they are not familiar with Samuelsson's technique, but most agreed that it could be a useful addition to the methods of monitoring if its utility is confirmed.

"What we have problems with now is finding those long-term levels of radon, so (the new technique) would be helpful," said Richard Hopper, acting chief of the EPA's evaluation branch.

EPA to Investigate

Hopper said the EPA will take a close look at the new technique.

Radon is a colorless, odorless gas that is produced by the breakdown of the minute quantities of uranium in granite and some other types of rock. It seeps through the ground and into the basements of houses, where it often collects in much higher concentrations than are present outdoors.

The gas then breaks down into so-called daughter isotopes that bind to small particles of dust in the air, which are inhaled and lodge in the lungs. As these daughter isotopes continue to break down in the lungs, they release radiation that can cause lung cancer.

Radon levels are now most commonly measured by leaving a small piece of plastic in an unobtrusive spot in the house for a long period of time. As the radon and its daughter isotopes break down, they emit radiation, called alpha particles, that leaves a scar on the plastic. At the end of the year, the number of scars on the plastic is counted under a microscope.

Measuring Required

This method is accurate, but it gives a measure only of the amount of radon that was present when the plastic was in the home. A small number of states in the East, such as New Jersey and New York, where radon is a particular problem, require radon monitoring before a home is sold. This practice has generated controversy in some cases where homeowners allegedly have removed the monitoring devices for part of the monitoring period, thereby artificially lowering the amount of radon measured.

The new technique could solve that problem, experts said.

Samuelsson's technique is based on his discovery that one daughter isotope of radon called lead-210 binds permanently to any glass that it strikes. The amount of lead-210 and its daughter isotopes present on the glass can then be measured, using sophisticated radiation counters.

Samuelsson removed glass from windows and picture frames in houses where the radon history was well known and measured the amount of lead-210 and its daughter isotopes attached to the glass. He found that the amount of lead-210 was directly proportional to the amount of radon that was known through previous measurements to have been in the house, and that it thus provided a good measurement of the house's radon history.

He is now extending the studies to provide more data.

Samuelsson said the same technique could be applied to eyeglasses to monitor an individual's personal exposure to radon. But the technique would be useful, he said, only if the person did not clean the glasses very often.

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