Scavenged 239Pu 240Pu and 241Am from snowfalls in the atmosphere settling on Mt. Zugspitze in 2014 2015 and 2016

摘要

Concentrations of ²³⁹Pu, ²⁴⁰Pu, and ²⁴¹Am, and atomic ratio of ²⁴⁰Pu/²³⁹Pu in freshly fallen snow on Mt. Zugspitze collected in 2014, 2015 and 2016 were determined by accelerator mass spectrometry (AMS). For the sub-femtogram (10⁻¹⁵ g) - level of Pu and Am analysis, a chemical separation procedure combined with AMS was improved and an excellent overall efficiency of about 10⁻⁴ was achieved. The concentration of ²³⁹Pu ranges from 75 ± 13 ag/kg to 2823 ± 84 ag/kg, of ²⁴⁰Pu from 20.6 ± 5.2 to 601 ± 21 ag/kg, and of ²⁴¹Am was found in the range of 16.7 ± 5.0–218.8 ± 8.9 ag/kg. Atomic ratios of ²⁴⁰Pu/²³⁹Pu for most samples are comparable to the fallout in middle Europe. One exceptional sample shows a higher Pu concentration. High airborne dust concentration, wind directions, high Cs concentrations and the activity ratio of ^239+240Pu/¹³⁷Cs lead to the conclusion that the sample was influenced by Pu in Saharan dust transported to Mt. Zugspitze.