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Decay of Co 56 and Mn 56

1959; American Institute of Physics; Volume: 114; Issue: 6 Linguagem: Inglês

10.1103/physrev.114.1554

1536-6065

P. Kienle, R. E. Segel,

Advanced Chemical Physics Studies

Scintillation spectroscopy and coincidence techniques have been used to measure the decay schemes of ${\mathrm{Mn}}^{56}$ and ${\mathrm{Co}}^{56}$, both of which decay to ${\mathrm{Fe}}^{56}$. Gamma-ray energies and intensities were measured with the aid of a large NaI(Tl) crystal and a three-crystal pair spectrometer. Combining these data with $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}$ and $\ensuremath{\beta}\ensuremath{-}\ensuremath{\gamma}$ coincidence measurements, decay schemes are constructed for both nuclei. The $log\mathrm{ft}$ values for the various $\ensuremath{\beta}$ branches are examined and all of the $\ensuremath{\beta}$ branches from ${\mathrm{Co}}^{56}$ show higher than usual $log\mathrm{ft}$ values for allowed transitions. The ${\mathrm{Co}}^{56}$ decay to the second excited state in ${\mathrm{Fe}}^{56}$ is inhibited by a factor of \ensuremath{\sim}${10}^{3}$ while the ${\mathrm{Mn}}^{56}$ decay to the same state is inhibited even further. The allowed ${\mathrm{Mn}}^{56}$ decay to the first excited state in ${\mathrm{Fe}}^{56}$ is also slowed, while ${\mathrm{Mn}}^{56}$ decays to higher states proceed at more normal speeds. A discussion of the $\ensuremath{\beta}$-transition rates in terms of shell model assignments is given, from which some explanation of the $\ensuremath{\beta}$ rates results. The high inhibitions of the decays to the second excited state in ${\mathrm{Fe}}^{56}$ do not seem susceptible to a simple shell-model explanation.