Back in the days when I was a member of the Civil Defence Corps (yes, I *am that old!), we used dosimeters (jocularly referred to as "dozy-meters"). These were small, tubular machines with a calibrated dial with a logorithmic scale at one end which indicated the amount of radiation present.

Incidentally, how do *you pronounce "dosimeter?" We used to put the stress on the second syllable, thus - doh-SIM- mit-uh.