The disintegration of ${\mathrm{I}}^{124}$(4.2 days) has been studied with the help of magnetic spectrometers and scintillation spectrometers. The disintegration occurs 71% by electron capture and 29% by positron emission. Three positron groups were found having end-point energies of 2130 (46.0%), 1531 (46.4%), and 786 (7.5%) kev. The most energetic positron group has a shape characteristic of $\Delta I=\pm 2$, yes. Positron-gamma coincidence experiments show that this group goes to the ground state. Gamma rays of energies 2700, 2300, 2100, 1700, 1520, 1350, 723, and 603 kev together with annihilation radiation and Te $K$ x-rays have been found and the relative intensities measured. A disintegration scheme, consistent with the levels of ${\mathrm{Te}}^{124}$ as determined from the decay of ${\mathrm{Sb}}^{124}$, has been established. No beta rays were found, showing that a transition to ${\mathrm{Xe}}^{124}$ is highly improbable. The former work on ${\mathrm{I}}^{123}$(13.5 hours) has been substantiated and, in addition, it seems highly unlikely that any positrons are emitted from ${\mathrm{I}}^{123}$.

• Received 8 September 1958

DOI:https://doi.org/10.1103/PhysRev.113.628