NOTICE: The project that is the subject of this report was approved by the Governing Board of the National Research Council, whose members are drawn from the councils of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine. The members of the committee responsible for the report were chosen for their special competences and with regard for appropriate balance.

Support for this study was provided by the U.S. Department of Energy under Grant No. DE-FC01-99EW59049. All opinions, findings, conclusions, or recommendations expressed herein are those of the authors and do not necessarily reflect the views of the organizations or agencies that provided support for the project.

COVER PHOTOS. Clockwise from top: Plutonium-238 from the Savannah River Site, South Carolina; Cesium-137 and Strontium-90 capsules at the Hanford Site, Washington; 14-ton cylinder containing depleted uranium hexafluoride at the Oak Ridge Reservation, Tennessee.