Explained: rad, rem, sieverts, becquerels
Sometimes it must seem as though reports on releases of radioactive materials from Japan’s Fukushima Daiichi nuclear powerplant in the wake of the devastating earthquake and tsunami are going out of their way to confuse people. Some reports talk about millisieverts while others talk about rem or becquerels, when what most people really want to know is much simpler: Can I drink the milk? Is it safe to go home? Should people in California be worried? There are a number of reasons for the confusion. In part, it’s the usual disparity between standard metric units and the less-standard units favored in the United States, added to the general confusion of reporters dealing with a fast-changing situation (for example, some early reports mixed up microsieverts with millisieverts — a thousandfold difference in dose). Others are more subtle: The difference between the raw physical units describing radiation emitted by a radioactive...