Downwinder advocates are not buying that explanation. They say the National Nuclear Security Administration's tests overlooked crucial questions.

"They weren't thorough in their analysis," said Richard Miller, an expert on nuclear-testing fallout.

The Salt Lake Tribune obtained a copy of a report developed by the University of Nevada-Las Vegas radiochemistry laboratory.

The report, which examined the particles captured on air filters from a Milford air-monitoring station, concludes "no man-made radionuclides were detected."

In other words, bomb soot did not trigger those radiation spikes registered by a Milford air monitor.

NNSA spokesman Darwin Morgan repeated what his agency said two weeks ago - that his agency merely wanted to inform Utahns about the high gamma-radiation readings. According to NNSA, the Milford monitor detected penetrating gamma radiation at up to 7 times the average for the area, probably because naturally occurring radiation was being released from the ground and burning vegetation.

"We saw something and we got it out there so people could make decisions based on what we saw," he said Wednesday.

The new report dispels one theory advanced by Morgan's agency: that the naturally occurring element, radon, was the cause for the gamma spikes.

The radon theory was "couched in terms of possible, probable," said Morgan. "Their assumption was wrong."

The UNLV team found instead that gamma-emitting uranium, thorium, lead, beryllium, cesium-137 and potassium-40 all wound up on the filter. But there was no sign of anything unusual, like fallout.

David Shafer of the Desert Research Institute, which oversees the fallout radiation monitor network, said more tests are planned to examine alpha and beta radiation, but high levels are not expected, given the two, week-long tests already done and the three back-up tests used for confirmation.

Miller, a researcher who has developed an almanac of nuclear test fallout, attacked the tests for taking too long and for overlooking key questions, including how much alpha and beta radiation the fire released.

"It's taking a ridiculously long time to determine what's in that stuff, and that's unacceptable, unacceptable, and you can quote me on that," he said.

And, commenting on the lack of data on other forms of radioactive material in the fire smoke, he added: "That doesn't sound like sound science. It's terrible science, and you can quote me on that, too."

fahys@sltrib.com