The nuclear β-rays of radium D

The radium D. E. disintegration is of special interest because of the very low energy of the disintegration electrons. It appears probable that more than half of these are emitted with less than 4 kV energy so that the energy change is less than in any other known nuclear disintegration. While there has been much uncertainty about the energies of the nuclear electrons, certain other facts about the transformation appear to be well established. In nearly every disintegration the product nucleus of radium E is left excited 47 kV above the ground-level. The resulting γ-ray is very strongly internally converted in the L and outer atomic levels so that only about 3-5 γ-quanta escape from the parent atom in 100 disintegrations. These results have been established by expansion chamber observations of the β-rays and by observations of the effects produced by the unconverted 47 kV γ-quanta (Bramson 1930; Stahel and Sizoo 1930) and the L charac­teristic X -radiation which is emitted as a consequence of the ejection of a secondary β-ray from the L level by the internal conversion (von Droste 1933; Stahel 1935).

Nuclear spin of radioactive elements

There seems at present to be rather definite evidence that the rate of radio-active disintegration, and excitation of the product-nucleus usually connected with it, is largely affected by the values of nuclear angular momenta. It was shown by the author that the existence of intense components of α-ray-fine-structure indicates that the disintegrating-, and the product-nuclei possess different spins. The angular momenta received in this case by α-particles of the normal group (transitions between normal states of both nuclei) will reduce its probability of escape in favour of other groups corresponding to the formation of the excited product.