Investigating the Geometrical Acceptance of the Counter with a Source

The concept of geometrical acceptance of a detector is discussed, as the ratio between the number of particles which arrive to the detector and the number of particles emitted by the source. Various measurements are then reported to show how the acceptance depends on the distance between the source and the Geiger counter, first assuming a geometry with a point source, then a different geometry where the size of the source cannot be considered as negligible with respect to the counter sensitive area.