A comparison of some methods of estimating radium
The quantitative determination of the small amounts of radium present in the atmosphere, spring waters, minerals and rocks involves two steps: (1) The quantitative separation of the radium emanation in a known weight of the sample and (2) measurement of the ionization current produced by the emanation in a calibrated electroscope. Granting that we have accurate methods of separating radium emanation, the other problem of measuring the ionization of current and the calibration of the electroscopes for quantitative work must be given careful study, because the results ultimately depend upon the calibration constants of the electroscopes used. In the estimation of radium, the electroscope corresponds to the weights and analytical balance in ordinary quantitative chemical analysis. An electroscope is said to be standardized or calibrated when we know the quantity of radium, (or uranium) represented by some constant of the instrument. The present investigation includes the calibration of three types of alpha ray electroscopes extensively used for the determination of small quantities of radium by the emanation method. The known quantities of the radium emanation required in these experiments were obtained, (1) from uraninite (Pitchblende) of known uranium content, and (2) from a standard radium solution. In this connection a comparative study was made of the types of apparatus employed by several investigators for the separation of the emanation and its transfer to the electroscopes, with a view of standardizing the existing methods for the calibration of electroscopes.