A method of absolute intensity measurement of intensive impulse fluxes has been described. Method and primary absolute detector devicephotoionization quantometerare based on fundamental cross sections of photoionization and ionization by electron impact. New soft X-ray optic elements multilayer mirrors (MLM) were tested and used for constructing a 10-channel spectroanalyzer (polychromator) for photon energy range 0.1-1 .O keV. Results of polychromator using at "Angara-5-1" installation are presented.