Table I. Radioisotopes Present in Plankton Collected soon after Fallout Per cent of Isotope Half life total radioactivity Bomb debris Np 239 2.3 days 69 y237 6.8 days 3 Fission products Mo29-T¢99™ 66 hours 12 Te 132_7132 77 hours 8 Ru 103-Rpt03 40 days Rul05-Rpl05 36 hours?) Ru106-Ry106 ‘ 3 1 year Ba!40.1,,140 12.8 days 2 Cel4i-p,yi4l 33 days 2 65 days ] 285 days <1 Zr95-Nb95 | Cel44_pyl44 100+ 1) Data from Lowman, (1960): average value for six samples collected less than 48 hours post shot; fallout from one detonation, Rehoboth survey, (1958) 2) Half life of daughter