a radiation counter in which the strength of each electric pulse generated per count is proportional to the energy of the particle or photon producing the pulse, alpha particles producing a different electric pulse from beta rays.
British Dictionary definitions for proportional counter
an instrument for detecting and measuring the intensity of ionizing radiation. It is similar to a Geiger counter but operates at a lower potential difference such that the magnitude of the discharge is directly proportional to the number of gas molecules ionized by the detected particle. This may permit the identification of the particle or the determination of its energy