[en] Numerical calculation of the efficiency of xenon ionization chambers used for X-ray medical computer tomographs is conducted using Monte-Carlo method. The considered detector represents xenon ionization chamber with complete collection of carriers. Calculation of sensitivity of such a detector is boiled down to calculation of energy release in the sensitive volume of detector filled with a gas. Besides contribution of electrons producted in the inlet aperture substance and electrons of this detector into energy release is estimated and contribution of electrons producted in the neighbour detector elements is determined, as well. Calculation is made for 40, 60, 80, 100, 120 and 140 keV energy photons. Analysis of calculation results has shown, that electrons producted in gas layer contribute mainly into energy release. Effect of neighbouring detectors is maximum 1.7%. Contribution from electrons formed in electrode and inlet aperture constitutes 2.5-8%