The use of radioactive isotopes for determining saturated vapour pressure

Abstract

A brief survey is given of methods, techniques and experimental arrangements for measuring vapour pressure using radioactive isotopes. Determination of the vapour pressure by a static method from a direct measurement of the radioactivity of the vapour with a counter, from the activity determined by a photographic method or by radio-chemical methods, is described. Papers concerned with the measurement of the vapour pressure by the boiling point and the jet-method are discussed. The variations in Langmuir's method depending on the evaporation of material from a filament and from a crucible are analysed. The vapour pressure of liquid metals and liquid alloy components is calculated from the activity of the condensate. A variation of the method is described in which the vapour pressure is determined from the radioactivity of part of the condensate. The integral and differential variations (integral with collection of all the vapour and differential with collection only of part of the vapour phase) of Knudsen's method are discussed, together with results of vapour pressure measurements of elements and alloy components by radiometric analysis of the condensate. The last section describes measurements of vapour pressure by the isotope exchange method. A table is given showing the comparative sensitivity of the different methods of measuring vapour pressure.