Study of the $K$ Capture—Positron Ratio of the Transition ${\mathrm{I}}^{126}$ (2-) →${\mathrm{Te}}^{126}$ (2+)

The relative probabilities of $K$-electron capture and of positron emission have been measured for the transition of ${\mathrm{I}}^{126}$(2-) to the first excited state of ${\mathrm{Te}}^{126}$(2+). Direct measurement by a triple-coincidence method of the $\frac{K}{{\beta }^{+}}$ ratio gave the value 145±4. The energy of the positron transition to the ground state (2- → 0+) was found to be 1.129±0.005 Mev. The energy of the inner positron transition was determined to be 0.459±0.007 Mev by subtraction of the measured energy of the first-excited state of ${\mathrm{Te}}^{126}$, 0.670±0.005 Mev, from the ground-state-transition energy. The $\frac{K}{{\beta }^{+}}$ ratio of the 2- → 2+ transition and the ratios for analogous transitions occurring in ${\mathrm{As}}^{74}$ and ${\mathrm{Rb}}^{84}$ are compared with ratios computed from a model based on shell considerations. Measurements were made also of the two higher energy positron spectra of ${\mathrm{I}}^{124}$; the end-point energies were found to be 2.136±0.010 Mev and 1.53±0.02 Mev.