Emanation Method

in chemistry, a physicochemical method of deriving information about the properties of solids from measurements of their emanation. The concept was first proposed by L. S. Kolovrat-Chervinskii at the beginning of the 20th century.

In the emanation method, the solid substance under examination is impregnated or otherwise treated with a trace amount of a parent substance—usually radium, which forms the radioactive gas radon, or radium emanation, upon radioactive nuclear disintegration. The specimen is then placed in a special hermetic vessel, and a stream of gas transfers the radon from it into a chamber for the measurement of radioactivity. Observations are made of changes in the emanating power that occur over a period of time and as a result of such treatment as heating and grinding the specimen. Emanation curves are then drawn, showing the variation of emanating power with such factors as time and temperature. These curves help explain exactly what processes (such as recrystallization, dehydration, and polymorphic conversion) occur in the specimen and under what conditions. The emanation method is most often used in combination with thermal analysis in what is known as the thermal emanation method.

In the 1950’s, a modification of the emanation method was introduced. Instead of adding parent radium atoms to the sample, scientists began directly adding radioactive atoms of an inert gas, such as radon-222, xenon-133, or krypton-85. The emanation rate of these atoms from the solid substance into the surrounding atmosphere is studied.

The emanation method is used to determine, for example, the temperature of phase transitions, the temperature of the initiation and termination of solid-phase reactions, and the glass-transition temperature of polymers.