Low Energy Alpha-Particles from Radium

Abstract

The large alpha-ray spectrograph and the sensitive track method of detection, as used for studying the polonium alpha-particles, have been used to investigate the alpha-ray spectrum of radium. Thin and uniform radium sources were freshly prepared by depositing radium carbonate on platinum rods, using a modified method of Hahn and Meitner. Microscopic examination has revealed a line at 4.615 Mev, which is identifiable with that found by Rosenblum. From 0.5 to 0.9 Mev below the main line five previously unknown groups have been found. The intensities of the first line and of these last ones are, respectively, about 1800 and 50-20, if the intensity of the main line is set as 100,000. As in the polonium case, if the particle groups come from the nucleus as all experiments have indicated, the ordinary alpha-decay theory is in serious disagreement with the experiments, for the theoretical intensity varies with energy much more rapidly than the observed intensity. Therefore, a mechanism other than a simple penetration through the static potential barrier may be needed. Attempt has been made to explain these results by assuming a strong interaction between the outgoing particle and the rest of the nucleus. This interaction may imply a transfer of kinetic energy from the particle to the residual nucleus, which will then make the decay probability appear much larger. The total probability of decay and the resultant excitation of the nucleus are discussed in terms of this tentative mechanism.