Decay ofGa66andCu66

The 9.5-hour decay of ${\mathrm{Ga}}^{66}$ and the 5.1-minute decay of ${\mathrm{Cu}}^{66}$ have been studied by a variety of techniques including gamma-ray spectroscopy, internal conversion measurements, and angular correlation studies. All but one of the 18 gamma rays observed have been ordered into a structure of 11 levels and the spins and parities of all but one of these levels have been determined. It is shown that ${\mathrm{Ga}}^{66}$ has spin zero and even parity and that its 4.166-Mev $\beta$ spectrum is a pure Fermi transition. The energy of the internal conversion line of the 4.300±0.005 Mev transition was measured with great care and this line may be useful for spectrometer calibration. The second excited state of ${\mathrm{Zn}}^{66}$, at 1.875 Mev, has 2+ spin and parity. The stopover transition from this state contains at least 10% $M1\mathrm{}$ radiation: the stopover to crossover ratio is greater than 100 to 1.