Disintegration Schemes of Radioactive Substances. VI.Mn56andCo56

Abstract

The radiations accompanying the decay of ${\mathrm{Mn}}^{56}$ and of ${\mathrm{Co}}^{56}$ were studied by means of the magnetic lens spectrometer and coincidence methods. Both of these nuclei decay to stable ${\mathrm{Fe}}^{56}$ as the product nucleus. Four excited states of the ${\mathrm{Fe}}^{56}$ nucleus are definitely established with excitation energies 0.845 Mev, 2.11 Mev, 2.66 Mev, and 2.98 Mev, respectively. De-excitation of the three high energy states always leads to the 0.845-Mev level and thence to the ground state. The negatron spectrum of ${\mathrm{Mn}}^{56}$ consists of three groups of maximum energies 2.86 Mev, 1.05 Mev, and 0.73 Mev, respectively, and relative abundance 60: 25: 15 leading to the first, third, and fourth of the excited states mentioned above. The positron spectrum of ${\mathrm{Co}}^{56}$ consists mainly of a single group of maximum energy 1.50 Mev, leaving the ${\mathrm{Fe}}^{56}$ nucleus in the 2.11-Mev state. Orbital electron capture also takes place involving several other excited states. Altogether the energies of eight gamma-rays emitted by the ${\mathrm{Fe}}^{56}$ nucleus are determined: 0.845 Mev, 1.26 Mev, 1.74 Mev, 1.81 Mev, 2.01 Mev, 2.13 Mev, 2.55 Mev, 3.25 Mev. Within the experimental uncertainty five of these energies appear to be the multiples 2, 3, 4, 5, and 6 of 0.425 Mev. All of the beta-ray spectra involved seem to have the "allowed" shape of the Fermi theory. The significance of this and of the relative probability of orbital electron capture is discussed in terms of the tensor interaction. It appears that all of the transitions should involve nuclear angular momentum changes $\ensuremath{\Delta}J=\ifmmode\pm\else\textpm\fi{}1$ or $\ensuremath{\Delta}J=0$, with or without parity change. From the disintegration schemes one obtains the mass differences between neutral atoms, namely, ${\mathrm{Mn}}^{56}$---${\mathrm{Fe}}^{56}$=3.98 mMU and ${\mathrm{Co}}^{56}$---${\mathrm{Fe}}^{56}$=4.96 mMU, and the threshold for the reaction ${\mathrm{Fe}}^{56}(p,n){\mathrm{Co}}^{56}:5.47$ Mev.