Lifetime measurements in ${}^{93}\mathrm{Nb}$ from photon and inelastic neutron scattering

The low-spin structure of ${}^{93}\mathrm{Nb}$ has been studied using the ${}^{93}\mathrm{Nb}$$(\gamma ,{\gamma }^{\text{'}})$, ${}^{93}\mathrm{Nb}$$(n,n^{\text{'}}\gamma )$ and ${}^{94}\mathrm{Zr}$$(p,2n\gamma \gamma )$${}^{93}\mathrm{Nb}$ reactions. Lifetimes were determined from both ${}^{93}\mathrm{Nb}$$(\gamma ,{\gamma }^{\text{'}})$ and ${}^{93}\mathrm{Nb}$$(n,n^{\text{'}}\gamma )$ measurements. Branching ratios were measured, and multipolarities and spin assignments were determined from the ${}^{94}\mathrm{Zr}$$(p,2n\gamma \gamma )$${}^{93}\mathrm{Nb}$ angular correlation experiment. From $M1$ and $E2$ strengths, the $J^{\pi }=9/2^{+}$ and $7/2^{+}$ states at 1297.1 keV and 1483.6 keV, respectively, are proposed as members of the quintet of mixed-symmetry states associated with the $\pi 1g_{9/2}\otimes (2_{1,\mathrm{MS}}^{+}$,${}^{92}\mathrm{Zr}$) configuration. The large $B(M1)$ values determined in ${}^{93}\mathrm{Nb}$ cannot be explained within the weak coupling limit of the interacting boson fermion model.

Figure 1

(a) Angular correlation plot for the 338 keV transition gated by the 744.2 keV γ-ray $(9/2^{+}\to 7/2^{+}\to 9/2^{+})$. The fit to the data gives a mixing ratio of ${\delta }_{338}=-0.12(3)$. This value is in good agreement with previous work, where ${\delta }_{338}=-0.12(5)$ was determined [57]. (b) The 553.1 keV transition gated by the 744.2 keV γ-ray $(9/2^{+}\to 7/2^{+}\to 9/2^{+})$ with a fit to the data of ${\delta }_{553}=-0.03(5)$. Dashed lines indicate other angular correlation fits with unlikely spins for the 1297.4 keV level. The Gaussian width of the magnetic substate distribution, usually found to be between 2 and 3, was fixed to $\sigma =2.5$, from fits to previously known transitions in ${}^{93}\mathrm{Nb}$. The ${\chi }^2$ values given in our angular correlation fits are given by the total ${\chi }^2$ divided by the “number of correlation groups − 2.”

Figure 2

Photon scattering spectrum from ${}^{93}\mathrm{Nb}$ in the energy range from 1.9 to 2.2 MeV. The spectrum was measured at a scattering angle of ${127}^{°}$. Calibration (${}^{27}\mathrm{Al}$), background (Bg), and single-escape (SE) peaks are also labeled.

Figure 3

Doppler-shift attenuation data for γ-rays deexciting (a) the 1483.6 keV level and (b) the 1968.9 keV level.

Figure 4

${}^{93}\mathrm{Nb}$ partial level scheme showing the positive- and negative-parity (left side) one-phonon states, and the ten levels excited in the ${}^{93}\mathrm{Nb}$$(\gamma ,{\gamma }^{\text{'}})$ experiment with their respective branches. The thicknesses of the arrows are proportional to the relative intensities of the γ-rays depopulating a particular state and were determined from the ${}^{94}\mathrm{Zr}$$(p,2n\gamma \gamma )$ coincidence data.