K -electron capture, nuclear isomerism and the longperiod activities of titanium and scandium

Abstract

Recent work in the field of induced radioactivity has revealed a number of interesting phenomena. Thus it has been shown that certain nuclei which emit positrons may also transform to the same final nucleus by capturing an electron from the extra-nuclear structure. Another effect, closely linked with this, and for which experimental evidence has recently been obtained, is that if two nuclei with the same atomic weight A (isobars) but with atomic numbers Z and Z + 2 respectively, are both stable, the intermediate nucleus of atomic number Z + 1 (atomic weight A ) is unstable with respect to both of them and so decays by “ branching”. The intermediate nucleus in general transforms to the nucleus of atomic number Z by electron capture and to the nucleus of atomic number Z + 2, by emitting a negative electron. More unexpected amongst recent results is the not uncommon occurrence of nuclei with the same atomic number and atomic weight but with different activities. This is known as nuclear isomerism. Before its discovery in induced radioactivity its existence was, however, already known from Hahn’s work on the naturally radioactive substances uranium Z and uranium Y .