A new formula linking the shape of survival curve to the inactivation probabilities after different numbers of cell hits has been derived. It has been used in analyzing recent experimental data obtained with monolayer cells irradiated at definite values of LET (in different parts of Bragg peaks). The new approach allows not only deriving the values of inactivation probabilities at given LET values; unexpected consequences seem to follow especially for inactivation characteristics of carbon ions in different parts of the Bragg peak, too.