Research of interaction of β-radioactive radiation with biotissue of an organism is lead. It is shown, that during electrons moderation there is a brake electromagnetic radiation usually in an X-ray range. There are derivatives of the formulas in not relativistic and relativistic variant for a finding of dependence of a flux brake electromagnetic radiation from frequency, of charging number elements of a biotissue, of a parameter of efficiency braking of electrons, of initial intensity of a flux of electrons and initial energy of electrons, is given.