Measurements of fallout from the Chernobyl reactor accident in air, rainwater, soil and grass are reported. The concentrations of 16 radionuclides of the elements Nb, Mo, Ru, Sb, Te, I, Cs, Ba and Ce were obtained by γ-ray spectroscopy. In a few samples the 0-and α-emitters •••'•Sr, 23i,23 'Pu and 24, Cm were measured by radiochemical techniques. From several isotopie ratios information on the status of the reactor is derived: end of the chain reaction, exposure time of the fuel, and contribution of plutonium fission. The relative concentrations of various fission products in aerosol, soil, and grass were found to be identical whereas rainwater showed an enrichment of Mo, Ru, Te and I compared to Cs and Ba during the first week. The composition of the airborne fallout is compared with the calculated inventory and the reported release pattern. The elements are found to fall in four groups: (i) Sb, Te, I, Cs; (ii) Mo, Ru; (ni) Sr, Ba; (iv) Nb, Ce, Np, Pu, Cm with relative concentrations of roughly 1: 10" 1 : 10" 2 :10" 3 compared to the inventory. This indicates a depletion of the less volatile elements in the release from the damaged reactor and during transport. The airborne activity was found to be attached to small particles of < 1 Mm size. Iodine was present mainly in the form of species not retained by ordinary aerosol filters. Dry fallout has contributed about 75 % of the deposition of Cs and Ba and about 50% of Ru, Te and I with the major deposition during May 2 and 5, 1986. The total deposition of "Sr, 131 Csand "•Puis estimated to be 0.02, 1.5 and < 1 X 10" 4 kBq/m 2 , which has tobe compared with values of 2, 4 and 0.1 kBq/m J , respectively, measured before the accident.
