Abstract
Cs and 241 Pu (via 241 Am) concentrations were measured γ-spectrometrically on air filters from the early 1960s (mainly from 1964–66) from Vienna, Austria, and an alpine station in Salzburg, Austria. Accelerator mass spectrometry (AMS) was used to determine 240 Pu/ 239 Pu, 236 U/ 238 U and 233 U/ 236 U atom ratios as well as 236 U, 239 Pu and 240 Pu atom concentrations. The maximum 236 U/ 238 U atom ratio of these unique undisturbed global fallout samples was (1.19 ± 0.31) × 10 5 in spring 1964. The 233 U/ 236 U atom ratios were found within (0.15–0.49) × 10 2 and indicate that the weapons tests of the early 1960s can be excluded as 233 U source. The 236 U/ 239 Pu atom ratios were calculated in the range of 0.22–0.48.