Tuesday, November 18, 2008

Personal Radiation Detectors and Law Enforcement

Personal Radiation Detectors (PRDs) should not be used as a standalone law enforcement mechanism.

Common items--bananas, spinach, peanuts, brazil nuts, pottery, kitty litter, patients with recent radiation treatment for cancer--emit gamma radiation that will cause false positives in PRDs. As an example, the Port of Long Beach has over 250 false positives per day.

PRDs as a standalone radiation detection mechanism for law enforcement purposes is probably a poor strategy due to these excessive numbers of false positive readings from such innocuous sources, an inability to detect beta radiation, and unreliability in detecting heavily shielded sources. PRDs, as I understand it, are meant to be used in conjunction with other radiation detection technology (e.g., imaging systems and spectrographic monitors) in a "layered" defense.

Thus, stopping or searching a person based solely on a PRD positive reading, in my opinion, would be unwarranted (and probably a violation of his or her Fourth Amendment rights--although, of course, this is for the courts to decide).

[Note that I called detection of radiation from bananas, kitty litter, etc. by PRDs "false positives" above. These are false positives (Type I errors) only in the sense that PRDs are functionally devices to look for "bad stuff," and they identify "bad stuff" a lot more than it is actually present. Note, however, that these detectors are largely correct in identifying gammas sources. (Their actual false positive rates (i.e., an indication of detection of gamma radiation when there is no source) is more like 1 or 2 percent)).]

3 comments:

Tom said...

Bananas and kitty litter are only a problem with the very large portal monitors and cargo container detectors that are calibrated to detect very small changes in radiation level. PRD's are generally not sensitive enough to detect these small changes in radiation level. The real problem is that nuclear medicine patients are hot enough to trigger an alarm from a PRD. For the last few years these patients are provided with a document to keep them from being subjected to unwarranted searches.

Carl Southwell said...

GAO-03-235T opined that "radiation detection pagers have limitations. DOE officials told us that they do not view pagers as search instruments, but rather as personal safety devices to protect against radiation exposure, and that the pagers have a limited range and are not designed to detect weapons-usable nuclear material. ... pagers are more effectively used in conjunction with other radiation detection equipment, such as portal monitors similar to what DOE is providing to Russia for use at its border crossings." Granted, this report is old and technology has improved, but, in your opinion, has technology improved enough for first responders to use PRDs as a sole source for a probable cause search? I understand that some police departments are considering this as a crime fighting tool.

Carl Southwell said...

By the way, thanks for the correction on the banana and kitty litter issue.