Decay of the odd-oddN=Znuclide78Y

The odd-odd $N=Z$ nuclide, ${}^{78}\mathrm{Y}$ has been produced in the ${}^{40}\mathrm{Ca}{(}^{40}\mathrm{Ca},pn)$ reaction at 125 MeV. Recoiling fragments separated by their $A/Q$ values were implanted onto the tape of a moving tape collector and transported to a shielded position between two plastic β detectors and two Ge γ-ray detectors where β-γ coincidences were recorded as a function of time. γ rays with energies of 279 (100%), 504 (90%), and 713 (40%) keV, previously identified as yrast transitions in daughter ${}^{78}\mathrm{Sr},$ were observed and found to decay with a half-life of 5.8 (6) s. From the relative intensities of the γ-rays, a spin and parity of $5^{+}$ and $T=0\mathrm{}$ are assigned to the parent state in ${}^{78}\mathrm{Y}$ undergoing β decay. A production cross section of $4\pm 1\mu \mathrm{b}$ has been determined for ${}^{78}\mathrm{Y}$ by comparison of the counting rates with those of other reaction products with known cross sections. An upper limit of 500 keV can be set for the energy of this level relative to a possible highly deformed $T=1\mathrm{}$ $0^{+}$ ground state. From this limit, it can be inferred that $T=1\mathrm{}$ $\mathrm{pn}$ pairing is considerably quenched relative to such pairing in adjacent odd-odd $N=Z$ ${}^{74}\mathrm{Rb}.$ Two-quasiparticle rotor model calculations have been used to account for the structure of ${}^{78}\mathrm{Y}$ and adjacent nuclides.