air travel cosmic ray exposure and chest X- rays have much higher X-ray energies and the health consequences are appropriately understood in terms of the whole body volume dose. In contrast, these new airport scanners are largely depositing their energy into the skin and immediately adjacent tissue, and since this is such a small fraction of body weight/vol, possibly by one to two orders of magnitude, the real dose to the skin is now high. In addition, it appears that real independent safety data do not exist. A search, ultimately finding top FDA radiation physics staff, suggests that the relevant radiation quantity, the Flux [photons per unit area and time (because this is a scanning device)] has not been characterized. Instead an indirect test (Air Kerma) was made that emphasized the whole body exposure value, and thus it appears that the danger is low when compared to cosmic rays during airplane travel and a chest X-ray dose. However other professors in the UCSF radiology department disagree, saying that the radiation dose is low. "The conclusions are wrong", Ronald Arenson, professor of radiology, tells SF Weekly of his own institution's letter. "People who are totally unrelated to radiation wrote it. ... It was senior faculty at UCSF. They're smart people and well-intended, but their conclusions, I think, were off-base. They don't understand how radiation translates to an actual dose in the human body". Dr. Steve Smith, inventor of the body scanner in 1991, and president of Tek84, one of the companies that produces the machines, has stated that the concerns of Dr. Brenner and UCSF Scientists regarding the skin dose of backscatter scanners are incorrect. He states the values used for X-ray penetration were incorrectly based on the description of the imaging depth which describes what the instrument sees and is a few mm into the skin and the dosage depth which is deeper. He describes experimental proof that the X-rays have the same properties as any other X-rays and the penetration is correct to be averaged over the whole body. Dr. Smith has provided measured data from an operating body scanner to explain his position. In October 2010, The TSA responded to the concerns of UCSF researchers via the White House science advisor. Scanners also concentrate the dose in time, because they deliver a high dose-rate at the moment of exposure. High dose-rate exposure has been shown to cause greater