Abstract: For determining the partial pressure and concentration of a measuring gas which is in mixture with at least one additional gas according to an optical absorption technique, in which a beam of light having a predetermined intensity and alternatingly and cyclically having a first spectral distribution in which the light intensity will be reduced by passage through the measuring gas and a second spectral distribution in which the light intensity will not be reduced by passage through the measuring gas, is passed through such a mixture and its radiation intensity after passage through the mixture is measured in a radiation detector having an active element which is heated by the radiation and which produces an output representative of its degree of heating and composed of alternating measuring signal segments, resulting, respectively, from light having the first and the second spectral distribution, and adjacent signals segments are processed in order to compensate for various interference effects, the detector o

Abstract: A method is provided for separating gaseous or vaporous substances, especially isotopes, with different molecular weights and/or different gas kinetic cross sections, in which the mixture of substances to be separated is passed through separation nozzles. One of more skimmer diaphragms project into the flow path of the substances and are used to separate and remove fractions of different compositions, and several separation systems consisting of nozzles and skimmer diaphragms are arranged in a cascade. The cascade generates partial streams which contain the mixture of substances to be separated. The partial streams can contain an additional gas with each partial stream containing different fractions of additional gas.