Why geiger muller detector cannot measure energy?

A Geiger-Muller (GM) detector primarily measures the count rate of ionizing radiation rather than the energy of the radiation. It operates by detecting the ionization produced by radiation in a gas-filled tube, which results in a pulse that is counted. However, the pulses produced are not proportional to the energy of the incoming radiation; they only indicate the presence and count of detected events. Consequently, GM detectors cannot distinguish between different types or energies of radiation, limiting their use for energy measurements.