Counting efficiency

[2] Counting efficiency varies for different isotopes, sample compositions and scintillation counters.

It has been calculated that only some 4% of the energy from a β emission event is converted to light by even the most efficient scintillation cocktails.

[3] Proportional counters and end-window Geiger-Muller tubes have a very high efficiency for all ionising particles that reach the fill gas.

Nearly every initial ionising event in the gas will result in Townsend avalanches, and thereby an output signal.

However the overall detector efficiency is largely affected by attenuation due to the window or tube body through which particles have to pass.

Graphic showing relationships between radioactivity and detected ionizing radiation
Hand-held large area alpha scintillation probe under calibration using a plate source in close proximity to the detector.
Schematic of a Geiger counter using an "end window" tube for low penetration radiation. A loudspeaker is also used for indication.