The β/γ and delayed proton decays of mass separated A=141 isotopes with Z=63–66 were investigated with an on-line mass separator. Branching ratios have been redetermined for the total β decay of the 2.7(3) s, ${(11/2\mathrm{}}^{\mathrm{-}}$ isomer ${}_{}{}^{141}{}_{}{}^{}\mathrm{Eu}_{}^{\mathrm{m}}{}_{}{}^{}$ at 96.5 keV (${13}_{\mathrm{-}2}^{+4\mathrm{}}$%), and for the direct β feeding of the 1.58 keV ${(3/2\mathrm{}}^{+}$ level of ${}_{}{}^{141}{}_{}{}^{}\mathrm{Sm}$ in the decay of 40-s ${}_{}{}^{141}{}_{}{}^{}\mathrm{Eu}_{}^{\mathrm{g}}{}_{}{}^{}$ [73(5)%]. Detailed decay schemes have been constructed for the decays of the ${(11/2\mathrm{}}^{\mathrm{-}}$ isomer ${}_{}{}^{141}{}_{}{}^{}\mathrm{Gd}_{}^{\mathrm{m}}{}_{}{}^{}$ [11(2)% isomeric transition] and the ${(1/2\mathrm{}}^{+}$ ground state, ${}_{}{}^{141}{}_{}{}^{}\mathrm{Gd}_{}^{\mathrm{g}}{}_{}{}^{}$. Half-lives of 24.5(5) s and 14(4) s, respectively, have been determined for these isomers. A delayed proton branch of 0.03(1)% was identified in the decay of ${}_{}{}^{141}{}_{}{}^{}\mathrm{Gd}_{}^{\mathrm{g}}{}_{}{}^{}$. A detailed decay scheme was also constructed for 3.5(2)-s ${}_{}{}^{141}{}_{}{}^{}\mathrm{Tb}$ and a $J^{\pi }$${=(5/2\mathrm{}}^{\mathrm{-}}$ was assigned to its ground state, at variance with the systematics of heavier, odd-mass Tb isotopes. All γ-ray assignments to the various isotopes are based on xγ and γγ coincidences and on half-life measurements. A 0.9(2)-s half-life for ${}_{}{}^{141}{}_{}{}^{}\mathrm{Dy}$ was determined from its delayed proton decay. All spin assignments proposed in this paper are discussed in terms of Nilsson level diagrams and nuclear shapes.

• Received 25 July 1989

DOI:https://doi.org/10.1103/PhysRevC.40.2249