β-ray spectra of thorium disintegration products

In problems relating to atomic structure the study of β-ray spectra is becoming of increasing importance. It is therefore desirable that an accurate analysis should be made for as many substances as possible which emit β rays. This has been done in great detail by Ellis, and by Ellis and Skinner, for radium B and radium C, and they have shown that the γ rays which eject the electrons from the atoms can be arranged in a system of levels. Recently the author made an analysis of the β-ray spectrum of mesothorium 2, and found that most of the γ rays from this substance could also be accounted for by a system of levels. The β-ray spectrum of thorium B and of thorium C + D had previously been measured by Ellis and also by Meitner. Since that time the technique of the measurement of β-ray spectra has been greatly improved. Therefore, considering the importance of such measurements in modern atomic theories, it was most essential that an accurate analysis of the spectrum of these substances should be made. Moreover, the previous measurements for these spectra were based on the then accepted values for lines of the radium B spectrum, which recent work has .shown to need a small correction.