Small-scale variation in deposition of radiocaesium from the Chernobyl fallout on cultivated grasslands in Norway

Abstract

Soil samples from nine field experiments on cultivated grassland showed a variation in deposition of radiocaesium, expressed as the relative standard deviation, from 11 to 111% within an area of 16.5 × 10 m². At the site with the highest variability, situated in a mountainous region of south eastern Norway, a further study was performed. Double sampling including surface measurements with in situ gamma-spectrometry using a portable multi-channel analyser (3 × 3 in Nal detector) and limited soil sampling gave the same average deposition and standard error as an extensive soil sampling. There were no trends in the deposition within the experimental field and most of the variation was found within plots (1.5 × 2.5 m²). ‘Hot spots’ were found in connection with small depressions (2–5 cm) in the terrain, and the area of a hot spot was estimated to be 100 cm² from field measurements with a Geiger–Müller counter.