Personal radiation dosimeter badges are the things that you may have seen people wearing in nuclear power plants, that measure how much radiation is in the immediate environment. Unfortunately, the devices don't provide real-time feedback - instead, they must be sent off to a processing lab, which determines the wearer's radiation exposure after the fact. Now, however, the U.S. Department of Homeland Security's Science and Technology Directorate (S&T) is working on a wallet-sized card that would serve the same purpose, but that could also be read on the spot using a handheld reading device. Called the Citizen's Dosimeter, it could be used to detect the presence of ionizing radiation caused by nuclear accidents or dirty bombs.

Currently in the blueprint stage, the dosimeter is being developed by the New York City-based National Urban Security Technologies Laboratory (NUSTL), which is managed by S&T.; The device is designed to incorporate commercially-available components, in order to keep production costs down. It will utilize the radiation-sensitive element tantalum, combined with a double-layer stainless steel filter. Tantalum was chosen from about half a dozen other materials, as it strikes a good balance between accuracy and minimal thickness.

NUSTL is also working on a portable reading device for the cards. The idea behind the system is that when emergency crews show up at the scene of a nuclear accident or terrorist attack, they could read the dosimeters of citizens in the area, to see if they have been exposed to dangerous levels of radiation.

Although it will reportedly be years before the Citizen's Dosimeter is available, the device has recently been awarded a patent. Although Homeland Security has developed numerous technologies over the years, this is the first one to ever be patented.