Acknowlecgments The author is indebted to Rolf Lange, Leonard Lawson, and Hoyt Walker of Lawrence Livermore National Laboratory for their assistance in developing the suite of computer programs used in the calculations. Grateful thanks are also due to Nathaniel Greenhouse * and Edward Lessard of Srookhaven National Laboratory for supplying me with meteorological and dose rate data for the Castle-Bravo test. Present affiliation: 94720. ad Lawrence Berkeley National Laboratory, Berkeley, California