Wednesday, January 31, 2007

Overly sensitive radioactivity detectors - no radiation is too small?

As more and more public venues put in radiation detectors in the aftermath of 9-11 and the general terrorist scare, it appears they are catching more patients with residual radiation left over from medical tests than terrorists.

BoingBoing and others are picking up this story as new, but in a post from March of last year I described a personal experience with this phenomenon from when I was in graduate school. It was at the NIST laboratory (complete with nuclear reactor) rather than a public venue with radiation detectors but the humor is the same. From the previous post:
"You must pass through radiation detectors to enter and leave the room where the experiments are performed to make sure that no radioactive material leaves the room for safety reasons. The detectors start by stepping in them or when they detect any radiation, this last property was the source of the fun.

During one of our trips to NIST, where the experiments were performed, one of the group had just undergone a medical test similar to the one of the woman above that involved injecting a radioactive tracer. The sensitivity of the radiation detectors at NIST was so high that this newly radioactive group member could set them off from 40 feet away. His residual radioactivity was so high that he could make you fail the test (proclaimed with loud alarms and flashing lights) while you were in the machine and he was far away. It was great (if a bit geeky) fun."
That recollection was inspired by a story about a woman driving who set off detectors intended to catch mobile radioactive terrorists.

Will someone please do the economics on this stuff: How many false alarms and the costs associated with them are equal to the prevention of the hypothetical attack? Keep in mind that the false alarms are many and the probability of attack is extremely tiny.

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