  The construction and characteristics of the cylindrical ion pulse ionization
chamber (CIPIC) with a working volume of 3.2 L are described. The chamber is
intended to register alpha-particles from the $^{222}$Rn and its daughter's
decays in the filled air sample. The detector is less sensitive to
electromagnetic pick-ups and mechanical noises. The digital pulse processing
method is proposed to improve the energy resolution of the ion pulse ionization
chamber. An energy resolution of 1.6% has been achieved for the 5.49 MeV
alpha-line. The dependence of the energy resolution on high voltage and working
media pressure has been investigated and the results are presented.
