The Decay ofI125

Abstract

The decay of ${\mathrm{I}}^{125}$ has been investigated. The nuclide decays entirely by orbital electron capture with a half-life of 60.0±0.5 days. An upper limit of 5×${10}^{-4\mathrm{}}$ was set for the fraction of ${\mathrm{I}}^{125}$ decaying to the 58-day isomer of ${\mathrm{Te}}^{125}$. By proportional counter and coincidence measurements it was established that all transitions go to the 35.4-kev level of ${\mathrm{Te}}^{125}$, which is a $d_{\frac{3}{2}}$ state. The ${\mathrm{I}}^{125}$ ground state can be assigned a $d_{\frac{5}{2}}$ configuration. The ratio of $L_{\mathrm{I}}$ to $K$ electron capture was determined to be between 0.18 and 0.45, with a most probable value 0.30. From these ratios, the energy difference between the ground states of ${\mathrm{I}}^{125}$ and ${\mathrm{Te}}^{125}$ was found to be between 95 and 215 kev, with the most probable value 115 kev. The corresponding $\mathrm{ft}$ values for the transition to the 35.4-kev level of ${\mathrm{Te}}^{125}$ fall in the range of allowed transitions.