Hatch's staff had provided this newspaper with a copy of Gerberding's letter, which the paper forwarded to Lyon for comment. That was the first he had seen it, and on Wednesday Lyon wrote a letter to Hatch replying to Gerberding's points.

Lyon wrote to Hatch that from 1986 to 1999, his group developed a dosimetry model to estimate a person's exposure to radiation from the Nevada Test Site.

The group used the model, and the details of the model were published in peer-reviewed journals, he wrote.

"Since the original development, variations of this very model have been used widely in radiation research, including by the CDC-funded Hanford (Wash.) Thyroid Disease Study and the National Cancer Institute study of the nationwide exposure to Iodine-131," radioactive material released by atomic explosions at the test site.

"It comes as a shock to us, as it will to radiation researchers worldwide who have been using our model for years . . . that the CDC is claiming that in the current study, there is 'a lack of scientifically defensible dosimetry,' " Lyon wrote.

Gerberding said the university was unable to reproduce the dosimetry from earlier work.

"This is not true," Lyon wrote to Hatch. "We did have difficulty getting our original dosimetry mode, written in 1989, to run again because of changes in the software and computer platforms, but we have always been able to reproduce the dosimetry.

"As mentioned, we also found some errors in the original model and corrected any problems we identified." The changes were summarized in a scientific paper submitted to a peer-reviewed scientific journal in February, he added.

Lyon told Hatch that a sub-study that was approved and originally funded would look at the effects of Nevada Test Site radiation on all other causes of death besides thyroid disease. No study has ever addressed the question, "and we will be unable to complete it because of the loss of funding," he wrote.

The Utah study is the only one in the United States attempting to actually examine individuals who were exposed to radiation to determine if they evidence of health effects, the letter says.

"We're trying to do it with the highest level of scientific credibility," Lyon told the Deseret Morning News.

So why has CDC pulled the plug on the study?

"If we knew, we would tell you," Lyon said.

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E-mail: bau@desnews.com