The Radioactivity ofGa66

The disintegration of ${\mathrm{Ga}}^{66}$ results in four positron groups with end-point energies and relative intensities of 4.144 Mev, 87 percent; 1.4 Mev, 4.3 percent; 0.878 Mev, 6.9 percent; and 0.403 Mev, 1.7 percent. Nuclear gamma-rays having energies of 1.03 Mev, 2.75 Mev and 4.8 Mev are observed. Measurement of the associated Auger electrons at 7.3 kev indicates that 34 percent of all disintegrations are by $K$-electron capture. The 4.14-Mev positron spectrum is found to have a shape characteristic of an allowed transition. In consideration of its high $\mathrm{ft}$-value, it is therefore inferred that this transition is once forbidden with a change of parity and a spin change of 0 or 1 unit. Furthermore, this transition does not go to the ground state of ${\mathrm{Zn}}^{66}$, but rather appears to be followed by the 1.03-Mev gamma-ray. The direct 5.17-Mev transition between ground states is found to proceed in less than 0.4 percent of the positron decays. This transition is apparently twice forbidden with a spin change of 3 units and is effectively outcompeted by the other less forbidden modes of decay.