Internal Homeland Security documents describing specifications for border-crossing scanners, which emit gamma or X-ray radiation to probe vehicles and their occupants, are raising new health and privacy concerns, CNET has learned.

Even though a public outcry has prompted Homeland Security to move away from adding X-ray machines to airports--it purchased 300 body scanners last year that used alternative technology instead--it appears to be embracing them at U.S.-Mexico land border crossings as an efficient way to detect drugs, currency, and explosives.

A 63-page set of specifications (PDF), heavily redacted, obtained by the Electronic Privacy Information Center through the Freedom of Information Act, says the scanners must "be based on X-Ray or gamma technology," which use potentially dangerous ionizing radiation at high energies, and "shall be capable of scanning cars, SUVs, motorcycles and busses."

"Society will pay a huge price in cancer because of this," John Sedat, professor of biochemistry and biophysics at the University of California at San Francisco, told CNET. Sedat has raised concerns about the health risks of X-ray scanners, and the European Commission in November prohibited their use in European airports.

The specifications do not say how Customs and Border Protection, or CBP, will notify people crossing the border about the radiation emitted by the devices, how frequently the devices will be tested to ensure they're operating properly, or whether travelers will be presented with a choice of declining the scan, which is an option at airport body scanners that use X-rays.

X-ray scanners made by American Science and Engineering are already in use at the busy San Ysidro, Calif., checkpoint. CBP, which says the level of radiation emitted falls within commonly accepted norms, is planning to announce details about the next round of scanner purchases on February 1.

Unlike, say, radio waves, ionizing radiation is dangerous because it can damage living tissue, rearrange chromosomes, and raise cancer risks. Whether the radiation is harmful depends on the dose: ionizing radiation at very low doses is ubiquitous in the environment, including from cosmic radiation, radon, and high-altitude air travel. Pregnant women are especially sensitive to high doses of ionizing radiation.

"This seems to be a massive escalation in the use of these systems," says Peter Rez, a professor of physics at Arizona State University who has studied the way the X-ray scanners work.

Rez says the name that Homeland Security has picked for its border scanners--"Low Energy Drive Through Portal Non-Intrusive Inspection Systems"--is highly misleading. "To call anything based on high energy X-rays 'low energy' is worse than 1984 doublespeak" because radiation emitted by the scanners "goes right through the person" sitting in a vehicle, he says. (High energy X-rays can penetrate not only human flesh, but steel plates that are multiple centimeters thick.)

For its part, Homeland Security says the dose is safe and based on commonly accepted government standards (PDF) established by the National Council on Radiation Protection and Measurement, which would permit 2,500 scans a year for each person. CBP's specifications also require the manufacturer to "perform an evaluation of the potential effect of radiation exposure on public safety on the proposed system." In addition, a CBP representative told CNET that the machines are currently only used in secondary inspections (most people go through just the primary inspection).

But Homeland Security did not respond, citing insufficient time, to a list of questions that CNET posed on Wednesday evening asking about independent testing that has been performed on the scanners that would measure the actual dose of radiation emitted. In the case of its airport scanners, Homeland Security's Transportation Security Administration initially promised to conduct such an analysis, but then backtracked, prompting criticism last fall from Sen. Susan Collins, a Maine Republican.

The dispute about radiation during border scans generally parallels the one about airport X-ray scanners, with Homeland Security saying they're safe, and researchers raising concerns that no independent testing has been done. A letter (PDF) that UCSF's Sedat and others sent the Department of Health and Human Services last year says that independent tests have not "been adequately performed for X-ray scanners, leaving us in a situation where a major untested technology is being used on a large segment of our population, and where any damage may not be apparent immediately, or recognized to be caused by the extra radiation exposure--an unprecedented state of affairs."

And the privacy concerns, too, are similar. Homeland Security's TSA says it "takes all measures to ensure passenger privacy" at airports. Its new "advanced imaging" millimeter wave machines at airports, which don't use ionizing radiation, do not display body outlines.

"They're potentially the same kind of images as people in airports," Ginger McCall, director of EPIC's open government program, says of the border scanners. They're also "capturing images of people essentially naked," she says.

The origin of the scanners can be traced back to a not-so-obvious source: President Obama's signature American Recovery and Reinvestment Act of 2009, better known as the stimulus bill. That awarded a $27.3 million contract to American Science and Engineering, or AS&E, to build 35 scanners, according to a description at Recovery.gov. Soon afterward, X-ray scanners appeared at the San Ysidro, Calif., checkpoint, sometimes called the world's busiest land crossing; other locations listed in the specification include El Paso, Texas, Columbus, N.M., and Nogales, Ariz.

Now Homeland Security wants more. The U.S. government convened a "pre-solicitation conference" in Washington, D.C., on November 29, 2011, according to a public procurement document. Another document says "Customs and Border Protection is very appreciative of all the responses received" and plans to publish a formal request for proposals for the next purchase on February 1.

AS&E, a publicly-traded company based in Billerica, Mass., boasts on its Web site that its Z Portal vehicle screening system can conduct "imaging from three sides simultaneously," and that "one scan is equivalent to flying one minute at altitude on an airplane."

Sedat, the biophysicist, says that the estimates of X-ray radiation dosage from AS&E and CBP are likely to be in error by several orders of magnitude because of the equipment they're using. He says: "If you have a laser pointer that you use for slides, it's a very bright beam. It's very hard to measure because it overwhelms a normal detector. You'll saturate the detector and you'll get the wrong answer. It could well come up with zero, or close to zero. And that's not right. It's not designed for handling that. The same is true for the ionization chambers they're using (as detectors)."

Rez, the physics professor, says the problem with X-ray scanners is that as the resolution increases, the corresponding dose leaps upward as well--and that AS&E's resolution has increased to approximately 5 millimeters. Another problem, he says, is failures: because the scan is conducted by having the vehicle move, if it stops in mid-scan, the radiation concentrated on one place would be above acceptable limits. "The energies are about three times the average energy in CT," he says, meaning an X-ray computed tomography scan.

A paper that (PDF) Rez and two-co-authors published in the journal Radiation Protection Dosimetry concludes that "serious consideration should be given to the possibility of unintended and unnecessary doses to passengers due to malfunctioning equipment."

Update January 30, 2012: We posed a number of questions to AS&E, which makes the Z Portal X-ray scanner, before this article appeared, but did not receive an answer. After it appeared, an AS&E representative contacted us to send a two-page letter from Joe Reiss, the company's vice president of marketing, that also did not answer the questions. Reiss did not respond to our question about whether AS&E will bid on Homeland Security's next round of X-ray scanner purchases, expected within the week. In response to our question about independent testing of radiation levels, an AS&E representative eventually said that "independent testing experts SGS have tested and certified the Z Portal to be in compliance with this and all other relevant radiation standards."

Part of AS&E's letter from Reiss is a word-for-word excerpt from one of the company's marketing brochures (PDF). The other points that Reiss raised in his letter: First, Z Portal's X-Ray tube has a peak energy of 225 kiloelectron volts (keV) and "does not use higher-energy X-rays" (ranging from 1,000 - 9,000 keV). Second, "X-rays are immediately shut off if the (vehicle) speed falls below the required threshold." Third, there are no privacy concerns because "the system cannot be used to identify an individual, or the race, sex or age of the person." Fourth, the Z Portal adheres to the American National Standards Institute (ANSI) standard N43.17-2009 "Radiation Safety for Personnel Security Screening Systems Using X-Ray and Gamma Radiation."

CNET offered to link to Reiss' full letter, but AS&E spokeswoman Betsey Rogers declined to post it on the company's Web site, saying it "would not serve the company well."