Detection of $^{133}$Xe from the Fukushima nuclear power plant in the upper troposphere above Germany

TL;DR

This study reports the detection of Fukushima-derived $^{133}$Xe in the upper troposphere above Germany, demonstrating that radioactive noble gases can trace atmospheric transport and distribution of nuclear releases at high altitudes.

Contribution

It introduces a novel measurement technique for ultra-low levels of $^{133}$Xe in aircraft-collected air samples, enabling detection of Fukushima radionuclides in the upper troposphere.

Findings

$^{133}$Xe was detected in the upper troposphere above Germany.

The radioactive plume reached the tropopause and was hemispherically distributed.

High-altitude arrival of the plume occurred days before ground-level detection.

Abstract

After the accident in the Japanese Fukushima Dai-ichi nuclear power plant in March 2011 large amounts of radioactivity were released and distributed in the atmosphere. Among them were also radioactive noble gas isotopes which can be used as tracers to test global atmospheric circulation models. This work presents unique measurements of the radionuclide $^{133}$Xe from Fukushima in the upper troposphere above Germany. The measurements involve air sampling in a research jet aircraft followed by chromatographic xenon extraction and ultra-low background gas counting with miniaturized proportional counters. With this technique a detection limit of the order of 100 $^{133}$Xe atoms in litre-scale air samples (corresponding to about 100 mBq/m$^3$) is achievable. Our results provide proof that the $^{133}$Xe-rich ground level air layer from Fukushima was lifted up to the tropopause and distributed hemispherically. Moreover, comparisons with ground level air measurements indicate that the arrival of the radioactive plume at high altitude over Germany occurred several days before the ground level plume.