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Influence of the Chemical State on the Lifetime of a Nuclear Isomer, Tc 9 9 m

1953; American Institute of Physics; Volume: 90; Issue: 3 Linguagem: Inglês

10.1103/physrev.90.430

1536-6065

Kenneth T. Bainbridge, M. Goldhaber, Elizabeth Wilson,

Nuclear Physics and Applications

Since a nuclear isomeric transition may take place by emission of either a gamma-ray or an internal conversion electron, the total rate of decay may be expected to vary with any change in electronic environment, such as a difference in chemical state. Differences in the decay constant of the isomer ${\mathrm{Tc}}^{99m}$ (6 hours) in different states of chemical combination were measured by the double ionization chamber balance method. $\ensuremath{\lambda}$ for this isomer is determined mainly by the internal conversion probability of a 2-kev transition which is followed promptly by a conveniently measurable 140-kev gamma-ray. Two compounds in the +7 valence state were compared: $\ensuremath{\lambda}(\mathrm{KTc}{\mathrm{O}}_{4})\ensuremath{-}\ensuremath{\lambda}({\mathrm{Tc}}_{2}{\mathrm{S}}_{7})=27.0\ifmmode\pm\else\textpm\fi{}1.0\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}\ensuremath{\lambda}({\mathrm{Tc}}_{2}{\mathrm{S}}_{7})$. $\ensuremath{\lambda}$ for the metal electroplated on nickel and reduced in ${\mathrm{H}}_{2}$ at 1000\ifmmode^\circ\else\textdegree\fi{}C for 1 hour $\ensuremath{-}\ensuremath{\lambda}({\mathrm{Tc}}_{2}{\mathrm{S}}_{7})=3.1\ifmmode\pm\else\textpm\fi{}1.2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}\ensuremath{\lambda}({\mathrm{Tc}}_{2}{\mathrm{S}}_{7})$. Errors are standard deviations. There is evidence for diffusion of the Tc into the nickel base and an accompanying decrease in $\ensuremath{\lambda}(\mathrm{Tc})$ of \ensuremath{\sim}2 parts in ${10}^{4}$ compared to pure crystalline metal. $\ensuremath{\lambda}$ of the metal was measured directly as 0.1148\ifmmode\pm\else\textpm\fi{}0.0005 ${\mathrm{hr}}^{\ensuremath{-}1}$, corresponding to a half-life of 6.04\ifmmode\pm\else\textpm\fi{}0.03 hours (limit of error). The methods used for internally checking the data and the operation of the apparatus are illustrated, and the statistics of the measurements are discussed.