The Beta-Rays of Mesothorium 1 and Radium D

Mesothorium 1 has been prepared from an old sample of thorium sulfate whose purity was demonstrated by measuring the rate of decay of thorium B prepared therefrom. The mesothorium 1 was shown to be free from contaminations of other thorium decay products and isotopic radioactive elements by measuring the rate of growth of mesothorium 2, and proving the absence of alpha-emitters. Magnetic deflection and aluminum absorption experiments have shown that the particles emitted are electrons whose maximum energy is 53,000±4000 electron volts. Samples of RaD and RaE, pure to within 0.3 percent, have been prepared. The momentum of the most energetic conversion beta-ray of RaD has been determined as 765±32 gauss cm, and the upper limit of the RaE continuous spectrum was found to be 5150±250 gauss cm. The upper limit apparently to be assigned to the primary beta-ray spectrum of RaD was determined as 546±10 gauss cm, or 25,500±1000 ev, in agreement with the determination of Richardson and Leigh-Smith. An estimate of the observed number of secondary beta-rays arising from the conversion of the 47.2-kev gamma-rays of RaD indicates the emission of five to ten such electrons per 100 disintegrations, in rough agreement with the results of Kikuchi and the predictions of Fisk for the $L$ conversion of dipole radiation, but in complete disagreement with the conclusions of Stahel and von Droste. Reasons for this disagreement are given.