The Department of Homeland Security (DHS) has used figures that may suggest a new type of nuclear weapons detectors is more reliable than warranted, the Government Accountability Office (GAO) stated in a report to Congress.

To be sure, the GAO report didn’t find that screening detectors installed at shipping ports are unable to detect nuclear weapons or materials secreted within cargo containers.

Rather, the watchdog agency found that test results may overstate the competence and reliability of those sensor systems in ferreting out threats.

The DHS Domestic Nuclear Detection Office is tasked with preventing smuggled nuclear weapons from entering the nation, and using the radiation detection portal monitors as one means of achieving that goal.

Specifically, the GAO focused on a new type of detector called advanced spectroscopic portal (ASP) monitors. The competing versions of the ASP are made by Raytheon Co. [RTN], Canberra and Thermo to screen trucks carrying cargo containers as they arrive at ports to be loaded on ships. The three contracts totaled $1.2 billion over five years.

So-called Phase 3 tests of how well the ASP systems work were interpreted by DHS in a way that the GAO asserted was flawed. For example, while DHS might say test results show ASP would identify a nuclear source in a container about half the time, actually it might be in a range of 15 to 85 percent of the time, the GAO found.

The DHS "reporting of the test results … makes them appear more conclusive and precise than they really are," the GAO report stated.

Congress mandated that ASPs cannot be procured at full production unless and until tests show the ASPs would be a major improvement over existing detectors.

The government review agency determined that "it is not appropriate to use the Phase 3 test report in determining whether the ASPs represent a significant improvement over currently deployed radiation [detection] equipment because the limited number of test runs do not support many of the comparisons of ASP performance made in the Phase 3 report."

These results, the GAO asserted, "could be misleading."

If an ASP correctly spots nuclear material every time, but the test is run just five times, then the most that can be concluded with a high level of statistical confidence is that "the probability of identification is no less than about 60 percent," the GAO stated.

DHS strongly disagreed with the report and some conclusions, and DHS refused to make two changes that GAO recommended, while agreeing to make a third change. The GAO, meanwhile, stands behind its report and its recommendations.

To read the GAO report titled "Combating Nuclear Smuggling: DHS’s Phase 3 Test Report on Advanced Portal Monitors Does Not Fully Disclose the Limitations of the Test Results" in entirety, please go to http://www.gao.gov on the Web.