[en] A technical description is given of an apparatus for remote sensing of the activity distribution along a radioactive source, which is based on gamma scanning. Test results with extended sources are reported and recommendations are made on improving the equipment. The apparatus was tested with line sources of californium-252, curium-244, and americium-241. The amount of californium-252 was determined by a relative method involving comparison of the neutron count rates from the test source and a standard one. The amounts of curium and americium in the sources were determined by a radiometric method after dissolution