With the recent spread of anthrax through the mail, the United States Postal Service (USPS) announced it would begin using radiation to kill the deadly bacteria. But some researchers wondered what would happen to the items being sterilized.

"People send all kinds of things in the mail -- photographs, computer disks, CDs," Braby said. "Gardeners send seeds through the mail. Doctors send biological samples for analysis through the mail. Irradiation won't make the mail radioactive, but beyond that, we need to know what happens to this stuff when it's irradiated."

Electron-beam, or e-beam, radiation is the same process used to irradiate food and medical equipment to kill harmful germs. Beams of electrons are fired at ultra-high speeds to break up the bacteria's DNA, killing the germs.

Researchers worried that the high doses of radiation needed to kill anthrax spores could damage items being mailed, Braby said.

"Seeds are pretty much destroyed and unprocessed film overexposed by the radiation," Braby said. "But CDs and computer disks survive the radiation process without damage. It's hard to visualize a physical process where electron-beam radiation would wipe out information stored in magnetic form, as in floppy disks and videotapes."

To test these theories, Braby and his colleagues at the Nuclear Science Center at the Texas Engineering Experiment Station used radiation on photographs and computer disks.

"We started with a dose of 5.5 kiloGrays, which is at the low end of what we would expect to be used for sanitizing mail," Braby says. "The radiation produced no errors in a 3½-inch floppy computer disk. I expected the photos to be bleached by the radiation, like they'd been left in the sun for a while, but the radiation did not produce a noticeable change in the color balance of the prints."

In the next run, Braby increased the radiation dose to almost four times the initial dose and include some writeable CDs in the test. At 20 kiloGrays of radiation, photos, computer disks and CDs again showed no signs of damage.

"Twenty kiloGrays is a large enough dose to kill the anthrax spores in the mail," Braby said. "That is probably the highest dose the postal service would use and there was no damage to the items we tested." - By Mark Evans


[Contact: Mark Evans]

14-Nov-2001