TSA officials have said that the radiation from a scan is equivalent to the amount received during two minutes of flight, and Rapiscan, the firm that makes the machines, argues that scans are safer than eating a banana, which contains potassium that is very slightly radioactive.
But a letter sent to White House science adviser John Holdren from five professors from the University of California, San Francisco and a sixth from Arizona State University argues that evidence made public of the system's safety is neither complete nor persuasive. The missive, first reported by ProPublica.org, a nonprofit investigative journalism organization, also asks why the TSA won't make scanners available for testing by independent scientists.
TSA's full body scanners use so-called backscatter technology, a fast-moving X-ray that bounces off the skin and creates an image of the passengers body. The beam does not pass through the body so the skin receives most the radiation exposure. The system has been evaluated by the Food and Drug Administration, National Institutes for Standards and Technology, and Johns Hopkins University Applied Physics Laboratory, according to ProPublica.
The group of scientists raising doubts about the scan's safety point out that the Johns Hopkins lab didn't test an actual airport machine, instead it used a system configured like one previously tested by TSA. They also noted that the device used to measure radiation levels, an ion chamber, could get overwhelmed by the high amount of radiation emitted by the backscatter device in a short period of time and might not provide accurate readings.
ProPublica reported that a number of scientists, including some who believe the amount of scan radiation to be minimal, say that more safety tests should be run, given TSA's plans for widespread use of the system.
Photo of full-body scan at Logan International Airport by John Tlumacki/Globe Staff