Study of 14C penetration into filters in primary productivity measurements using double side counting

The 14C-labeled assimilated organic matter penetrates into filters when primary productivity is measured but does not lie in a thin layer on the surface as has been assumed. This has been demonstrated by counting the filters from both sides with a Geiger-Mueller counter and confirmed by measuring the counting efficiency of individual filters. When the double side counting indicates deeper penetration, the Geiger-Mueller efficiency decreases as expected. (U.S.)