[en] Single-event spectra have been measured for ⁶⁰Co γ-radiation and filtered 200 kV X-rays for spherical and cylindrical volumes of sub-cellular size. For the measurements a novel wall-less proportional counter was developed which in a simple manner may be converted into a wall-counter. Measurements of the gas amplification of this counter yielded new values for the gas parameters A and B permitting the estimation of the multiplication of proportional counters at high electric potential on the collecting electrode. It further showed that the minimum effective diameter to be used is 0.1 μm if measurements of radiation with a low LET are made. The energy deposition with the highest probability was approximately 0.17 KeV/μm for the ⁶⁰Co radiation and approximately 0.65 KeV/μm for the X-radiation. (orig./BJ)