What is the difference between an active and a passive dosimeter?

The passive dosimeter at CERN is the personal, legal or DIS dosimeter. Dosimeters such as TLD or OSL are called 'passive' as they do not provide direct readouts and can operate without any active means. The measured dose is usually taken as an estimate for the effective dose which is recorded and reported after evaluation. The CERN DIS dosimeter should be called semi-passive as it has a battery and can be read at anytime at a reader station for a direct reading of the dose stored inside. But it is called passive as well in order to differentiate it from the active or operational dosimeter.

The active dosimeter is also called electronic, operational, alarm or DMC dosimeter. It provides a direct display of the accumulated dose as well as having some additional functions such as alarm threshold settings for dose or dose rate values. In addition it provides an audible and visual indication of the dose rate level. The dosimeter requires a battery to operate. This dosimeter is used for complementary dosimetry in the case of high radiation levels or for work and dose optimisation purposes.