Precise measurements of the energies of β -rays from radium (B + C)

Abstract

Precise measurements of the Hp values of β -rays from radium B have been made by Ellis and Skinner, Ellis, Scott and Rogers. Except for Rogers and Scott, who used the same methods, the results have differed from one another by amounts considerably in excess of the estimated probable errors. Measurements have been made by the authors of the Hp of eleven β -rays of radium B and of one of radium C. The values are based on eleven photographs of the spectra taken with a spectrograph of the type used by Ellis, and ten photographs with a spectrograph of the type introduced by Scott, the field strengths used ranging from 190 to 1050 G. The values obtained agree closely with those of Rogers for the lines measured by him; Rogers's values being 1931.7, 1671.3 and 1406.2 G-cm., and our values 1931.9, 1671.6 and 1406.2 G-cm. These values are considered correct to 1 part in 10 4 . The energies corresponding to the Hp values have been calculated using weighted mean values of e/m and c given respectively by Bearden and von Friesen. The error in the energies is approximately 1 part in 10 3 . Measurement of the Hp of the same line for a number of widely differing Precise measurements of the energies of fi-rays 171 values of H was a valuable check on the presence of systematic errors which had not been made by previous workers. An appreciable apparent increase of Hp with H was found, and a comparison of the calculated and observed line forms showed that this apparent increase was to be attributed to scattering of electrons in the emulsion. This effect appears to be one of the most important now limiting the accuracy obtainable by the present method.