| 407835 Natural Radioactivity and Radiation John H. Harley (HASL) ee Wayne M. Lowder (HASL) The measured levels of artificial radioactivity and radiation from weapons tests or the operation of nuclear facilities are often compared with the levels of natural background radicactivity. While many of these comparisons are not relevant it was felt to be worth while to have available a compilation of natural radioactivity and radiation levels. This compilation can then be used to provide general figures for cases where such comparisons are valid. The United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) has treated natural radioactivity in its 1958, 1962 and 1966 reports and other summaries of data are also available. The present compilation makes use of these previous collections and references rather than returning to the original papers on the subject. This was done both to avoid the labor of pre- paring new mean values and also to take advantage of the judgment of previous compilers. The data are presented as a series of tables indicating concentrations of radioactivity in various parts of the environment plus measurements and calcu- lations of the amounts in diet and man as well as the calculated resultant internal radiation doses. The external radiation dose is discussed separately. In addition to presenting an estimate of the mean value, the expected ranges are shown where the data are available. There has also been an attempt to stress measurements for the United States although these values should not be significantly different than worldwide values for the specific purposes of this compilation.