Sross * beta so " , ‘ Levets—of-B- radioactivity of plankton at Rongelap peolt, 29st 1958. Abstract This paper brings together available dataon the beta-aetivity of plankton at Rongelap Atoll for the period 1954-1958 including tie values of radioactivity reported in UWFL-42 and43, ‘Values are given on the ash as well as the wet weight basis, and ‘are shown to be more consistent on the asn weight basis. In a comparison of reSults from nets of different mesh size, no significant‘airference | appeared in levels of activity between fine and doarsemestikd Flank: ton nets. Rates of decay over a 2- 3year period aregiven Torshout | 30 samples. The fallout in 1956 is considered to have ‘contributed less than 1/100th as much radioactivity as that of 1954, and the 1°58 fallout, less than 1/20th that of 1956. The "1954-55 fallout affected primarily the northern, and the 1956and 1958 fallouts, the soutnern, parts of the atoll. Introduction 3 Plankton in Ronsselap Lagoon first took up large “anounte of ractoa:tivity from the fallout following Bravo detonation at Bikint Atoll on March 1, 1954, Since then, tne radioactivity has declined with only relatively slight additions from the“two ‘Bucceeding series of testain 1956 (Redwing) and 1958 (Hardtack). of UW?L-+3, plankton has been collected four times, 1967, ani Maren and August 1958. te Since the writing | . July 1956 and .