SHORT-RANGE VARIABILITY OF FALLOUT CS-137 IN AN UNERODED FOREST SOIL

Use of fallout Cs-137 for measuring soil erosion rates requires an acc urate estimate of the mean areal activity of Cs-137 of an uneroded ref erence site. To study the short-range variability of Cs-137 in a fores t soil, 16 profiles were sampled in a small area (8 x 8 m). Variabilit y was relatively low (CV = 16%), so that the mean areal activity (3163 Bq m-2) at this reference site was estimated with a relatively low al lowable error (< 10%) at relatiVely high confidence level (95 %). To o btain a satisfactory estimate of the mean areal activity of Cs-137 of reference sites, particularly those located in forest areas, it is sug gested to collect at least five subsamples, 1-10 m apart and composite them into a single sample for analysis.