An analysis of the fine structure of the α-particle groups from thorium C and of the long range groups from thorium C′

During the course of our previous measurements of the fine structure of α-particle groups we obtained preliminary measurements of the fine structure of the α-particle groups from thorium C. The results were in general agreement with those previously obtained by Rosenblum and Valadares, who photographed the α-ray spectrum. Our method of measurement appeared capable of yielding results of accuracy as high as 1 in 100,000 in velocity. Accordingly a series of measurements has now been carried out to examine the thorium C groups with much greater precision, and these experiments are described in the present paper. Our results provide information, which we believe to be of considerable accuracy, concerning the energy levels of the thorium C nucleus. When interpreted by Gamow's theory these measurements are in excellent agreement with certain γ-ray energies deduced from entirely independent β-ray measurements. By accelerating the particles in an electronic field we have in addition been able to measure the energy difference between the two most prominent groups of α-particles from thorium C, by a direct electrostatic measurement. This independent measurement is probably the most accurate determination of this energy difference, and is in excellent agreement with the energy of a strong γ-ray deduced from the β-ray spectrum measurement by Ellis.