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Radiation detector. Personal radiation detection tag resting on fingers. This device is worn by people who may be exposed to radiation, such as radiographers and nuclear power plant staff. Radiation affects the small squares inside the tag over time, and they are periodically analysed to ascertain the exposure levels over a set time period. If they are found to be higher than standard safety levels, then steps can be taken to reduce the individual's exposure. High levels of radiation can cause health problems such as dermatitis, organ damage and cancer. Tags such as these are cheap and easy to use, but provide no warning against large but short-lived doses. (KEYSTONE/SCIENCE PHOTO LIBRARY/KLAUS GULDBRANDSEN)