129I in precipitation using a new TOF system for AMS measurements

A new time-of-flight set-up for accelerator mass spectrometry with 129I was installed at the Maier-Leibnitz laboratory in Garching (Germany). The detector system consists of a TOF-system and an ionization chamber. A TOF resolution of 440 ps is obtained, the energy resolution is about 2%. The sensitivity of the complete system is 10−14 for the ratio of 129I/127I. The measurements of rain water samples from the time period between July 2003 and October 2004 showed a decrease of 129I concentration, of 129I deposition flux and of 129I/127I isotopic ratio compared to previous measurements of rain water in Southern Germany from 1988, 1989 and 1995. This decrease can be explained by a substantial drop in gaseous 129I emissions from the French reprocessing facilities.