Table III. Radioisotopes Present in Plankton Collected soon after Fallout Isotope Half life Per cent of total radioactivity Bomb debris Np239 2.3 days 69 y237 6.8 days 3 Fission products Mo99-T¢99m 66 hours 12 Te 132-1132 77 hours 8 Rul93-Rp103 40 days Rul05_pp,105 36 hours?) Ru106_Rp106 3 il year Bal40-7,a140 12.8 days 2 Cel4i1_p,141 33 days 2 Zr95-Np95 65 days 1 285 days <1 Cel44_p,144 100+ 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