Decay ofSr100and a ‘‘pairing-free’’Kπ=1+rotational band in odd-oddY100

The decay of ${}_{}{}^{100}{}_{}{}^{}\mathrm{Sr}$ (193 ms) to the low-spin ${}_{}{}^{100}{}_{}{}^{}\mathrm{Y}$ isomer (735 ms) was studied from mass-separated activity produced in thermal neutron fission of ${}_{}{}^{235}{}_{}{}^{}\mathrm{U}$. γ singles and γ-γ coincidence measurements resulted in the placement of 67 γ transitions in a decay scheme with 26 levels below 2 Mev. The multipolarities of low-energy transitions were determined from internal conversion electron measurements. Logft values were deduced using an absolute γ-ray intensity determination for the A=100 decay chain. The $1^{+}$ levels in ${}_{}{}^{100}{}_{}{}^{}\mathrm{Y}$ at 10.70 and 974.61 keV each receive ∼40% of the β feeding from ${}_{}{}^{100}{}_{}{}^{}\mathrm{Sr}$. A $K^{\pi }$ ${=1\mathrm{}}^{+}$ rotational band (with $1^{+}$, $2^{+}$, and $3^{+}$ levels at 10.70, 76.15, and 172.03 keV) is proposed which can be characterized as a nearly ‘‘pairing-free’’ band. Other levels in ${}_{}{}^{100}{}_{}{}^{}\mathrm{Y}$ are discussed in terms of two-quasiparticle Nilsson orbitals.