Radiation Detectors' Value Is Questioned

Several months later, the GAO found that the detection office's estimates for detection rates were overstated and that the costs of the machines were significantly understated.

As a consequence, lawmakers mandated that Homeland Security Secretary Michael Chertoff personally certify that the machines represent a significant operational improvement over existing equipment before they can be fully deployed.

Last year, the detection office conducted two rounds of tests of the machines, in part to support Chertoff's certification decision. The GAO concluded that the detection office's first round of tests were conducted in a biased way that "enhanced the apparent performance of the ASPs."

After Customs and Border Protection officials questioned the operational effectiveness of the machines in field tests, Chertoff announced a delay in his certification decision.

The GAO's new report focuses on the second round of detection office tests, called Phase 3. Detection office officials told government auditors that Phase 3 tests showed the machines "were as good as or better than" existing equipment "at detecting the presence of radiological source materials at low levels of radiological activity," the GAO report said.

The GAO also answered complaints from the detection office that auditors ignored the extent of the program's testing.

"In our view, regardless of how many tests are performed, the tests must employ sound, unbiased methodologies and [the nuclear detection office] should draw and present conclusions from the test results in ways that accurately and fully reflect the data and disclose their limitations, " the GAO report said.