Disintegration Schemes of Radioactive Substances. VII.Mn54andCo58

The radiations emitted by ${\mathrm{Mn}}^{54}$ and by ${\mathrm{Co}}^{58}$ have been studied by means of the magnetic lens spectrometer and coincidence techniques. ${\mathrm{Mn}}^{54}$ decays by orbital electron capture to an excited state of ${\mathrm{Cr}}^{54}$, followed by the emission of a 0.835-Mev gamma-ray. A study of the x-rays emitted following the capture process indicates that a large—or even an overwhelming—fraction of the captured electrons are $K$ electrons. Few if any capture transitions lead directly to the ground state. ${\mathrm{Co}}^{58}$ decays to a state of ${\mathrm{Fe}}^{58}$ 0.805 Mev above the ground state which in turn decays by the emission of a single gamma-ray. About 90 percent of the disintegrations of ${\mathrm{Co}}^{58}$ occur by $K$-electron capture. In the remaining 10 percent positrons of maximum energy 0.47 Mev are emitted. This ratio of the two modes of decay is consistent with the idea that the transition takes place with a change of angular momentum of one unit or zero, whether the parity changes in the transition or not, if the tensor theory of beta-decay is the correct one. The lowest known excited states of ${\mathrm{Cr}}^{54}$, ${\mathrm{Fe}}^{56}$, and ${\mathrm{Fe}}^{58}$ have excitation energies differing by less than five percent. The difference between the masses of the neutral atoms of ${\mathrm{Co}}^{58}$ and ${\mathrm{Fe}}^{58}$ should be 2.46±0.03×${10}^{-3\mathrm{}}$ a.m.u.