[en] A grid ionization chamber with cylindrical configuration was constructed for the measurement of the alpha spectra of very low level samples, which makes possible the measurement of radiation sources with an area of up to 2 m². The chamber has a volume of 400 l and is filled with technical argon with 5% addition of methane. Energy resolution of the detection system is 85 keV at 5.5 MeV, detection efficiency is 37% and the background at a range of 200 keV at 5.5 MeV is 10 cph. The detection limit is 1 mBq. The chamber may be used for measuring half-life of alpha-emitting rare earths, for dating sediments using the ²¹⁰Pb-²¹⁰Po method and geological samples using the U-Th method, for determining the composition and concentration of natural and technogenic alpha sources in natural samples. (J.P.)