Confusion has arisen about radiation exposure in the wake of the events at the nuclear plant in Japan. I had a colleague ask “Can we have a radiation detector to check our products coming in from Japan for radiation?” My colleague was confusing radiation with contamination. Nuclear radiation is emitted when the nucleus of an unstable isotope(radioisotope) decays to a more stable element. Alpha and Beta particles and Gamma radiation can be emitted by this process. An example is Iodine 125 decaying to the more stable Tellurium 125 as the final decay product; scintillation counters are used to detect the resulting Gamma radiation. Many labs use 125I in radioimmunoassays, the laboratory workers are thus exposed to a small amount of radiation when they work with this reagent. Exposure to radiation decreases and diminishes to nothing as the worker get farther and farther away from the 125I. The worker does not carry radiation home with her. The worker cannot become radioactive by being exposed to the 125I. However, if the worker should carry some of the 125I particles away the worker would then be contaminated. The radiation from the 125I would be detected before she left the laboratory and she would then be required wash and remove articles of clothing before going home. When radiation is detected in the water or soil as a result of a nuclear accident, it is the radiation emitted from a radioisotope particle contaminating the water and soil which is detected.