The electron-capture and ${\mathrm{\beta }}^{+}$-decay branchings (EC/${\mathrm{\beta }}^{+}$) and delayed proton decays of A=142 isotopes with 61≤Z≤66 and A=140 isotopes with 63≤Z≤65 were investigated with the OASIS facility on-line at the Lawrence Berkeley Laboratory SuperHILAC. Electron capture and positron-decay emission probabilities have been determined for ${}_{}{}^{142}{}_{}{}^{}\mathrm{Pm}$ and ${}_{}{}^{142}{}_{}{}^{}\mathrm{Sm}$ decays, and extensive decay schemes have been constructed for ${}_{}{}^{142}{}_{}{}^{}\mathrm{Eu}_{}^{\mathit{g}}{}_{}{}^{}$(2.34±0.12 s), ${}_{}{}^{142}{}_{}{}^{}\mathrm{Gd}$(70.2±0.6 s), ${}_{}{}^{140}{}_{}{}^{}\mathrm{Eu}$(1.51±0.02 s), and ${}_{}{}^{140}{}_{}{}^{}\mathrm{Gd}$(15.8±0.4 s). Decay schemes for the new isotopes ${}_{}{}^{142}{}_{}{}^{}\mathrm{Tb}_{}^{\mathit{g}}{}_{}{}^{}$(597±17 ms), ${}_{}{}^{142}{}_{}{}^{}\mathrm{Tb}_{}^{\mathit{m}}{}_{}{}^{}$(303±17 ms), ${}_{}{}^{142}{}_{}{}^{}\mathrm{Dy}$(2.3±0.3 s), ${}_{}{}^{140}{}_{}{}^{}\mathrm{Eu}_{}^{\mathit{m}}{}_{}{}^{}$(125±2 ms), and ${}_{}{}^{140}{}_{}{}^{}\mathrm{Tb}$(2.4±0.2 s) are also presented. We have assigned γ rays to these isotopes on the basis of γγ and xγ coincidences, and from half-life determinations. Electron-capture and ${\mathrm{\beta }}^{+}$-decay branchings were measured for each decay, and β-delayed proton branchings were determined for ${}_{}{}^{142}{}_{}{}^{}\mathrm{Dy}$, ${}_{}{}^{142}{}_{}{}^{}\mathrm{Tb}$, and ${}_{}{}^{140}{}_{}{}^{}\mathrm{Tb}$ decays. ${\mathit{Q}}_{\mathrm{EC}}$ values, derived from the measured EC/${\mathrm{\beta }}^{+}$ branchings and the level schemes are compared with those from the Wapstra and Audi mass evaluation and the Liran and Zeldes mass calculation. The systematics of the N=77 isomer decays are discussed, and the intense $0^{+}$→$1^{+}$ and $1^{+}$→$0^{+}$ ground-state beta decays are compared with shell-model predictions for simple spin-flip transitions.

• Received 31 August 1990

DOI:https://doi.org/10.1103/PhysRevC.43.1066