In a proportional counter comprising a detector for detecting radiation pulses, an energy channel for receiving detected pulses, preferably as pre-amplified, from the detector, and a pulse height analyzer for the analysis of pulses received from the energy channel, the background effect is reduced by measuring the detector charge pulse collection time caused by electron diffusion and the time interval between the detector pulses, comparing the measured times with predetermined limit values and, thereupon, discriminating all pulses which have collection times longer than the predetermined rise time that is have too long a rise time, or which appear at shorter intervals than the predetermined limit interval, that is are too close to an adjacent pulse be it a preceding or following pulse. In order to produce signals proportional to said rise time and said time interval, the pulses are preferably transformed in electronic circuits, for example, in two derivation circuits and one integration circuit. The predetermined limit values may be represented by two reference voltages and the discrimination is carried out by using known logic circuits.