Properties of high-spin states inTc95fromNb93(α, 2n)Tc*95(γ)reaction spectrometry: A test of the cluster-core coupling model

Abstract

The structure and properties of the high angular momentum states in $^{95}\mathrm{Tc}$ up to 5605 keV of excitation have been investigated via measurements of excitation functions of singles $\ensuremath{\gamma}$ rays and of $\ensuremath{\gamma}\ensuremath{\gamma}$ coincidences following the $^{93}\mathrm{Nb}(\ensuremath{\alpha}, 2n)^{95}\mathrm{Tc}^{*}(\ensuremath{\gamma})$ reaction with $\ensuremath{\alpha}$ particle energies between 17-30 MeV. From these experiments and from high-resolution singles energy, angular-distribution, and Doppler-shift attenuation measurements, the position and the decay properties of many high angular momentum states in $^{95}\mathrm{Tc}$ have been determined. Levels at 626.82 (${\frac{5}{2}}_{1}^{+}$), 882.16 (${\frac{13}{2}}_{2}^{+}$), 927.78 (${\frac{3}{2}}_{1}^{+}$), 957.07 (${\frac{11}{2}}_{1}^{+}$), 1084.95 (${\frac{5}{2}}_{2}^{+}, {\frac{7}{2}}^{+}$), 1178.60 (${\frac{7}{2}}_{2}^{+}$), 1214.53 (${\frac{9}{2}}_{1}^{\ensuremath{-}}$), 1307.19 (${\frac{11}{2}}_{2}^{+}$), 1514.8 (${\frac{17}{2}}_{1}^{+}$), 1549.4 (${\frac{15}{2}}_{1}^{+}$), and 1702.1 (${\frac{13}{2}}_{1}^{\ensuremath{-}}$) with the ${J}^{\ensuremath{\pi}}$ values in parentheses are confirmed. New levels at 2119.4 (${\frac{15}{2}}_{2}^{+}$), 2183.2 (${\frac{19}{2}}_{1}^{+}$), 2231.1 (${\frac{17}{2}}_{2}^{+}$), 2546.4 (${\frac{21}{2}}_{1}^{+}$), 2846.7 (${\frac{21}{2}}_{2}^{+}$ or ${\frac{21}{2}}_{1}^{\ensuremath{-}}$), 2905.8 (${\frac{19}{2}}_{2}^{+}$), 3038.8 (${\frac{19}{2}}_{3}^{+}, {\frac{17}{2}}^{+}$), 3515.2 (${\frac{25}{2}}_{1}^{+}$), 3657.7 (${\frac{25}{2}}_{2}^{+}$ or ${\frac{25}{2}}_{1}^{\ensuremath{-}}$), 3917.5 (${\frac{29}{2}}_{1}^{+}$), 4292.2 (${\frac{27}{2}}_{1}^{+}$), 4455.4 (${\frac{29}{2}}_{2}^{+}$ or ${\frac{29}{2}}_{1}^{\ensuremath{-}}$), 4761.0 ($\frac{29}{2}, \frac{33}{2}$), and 5604.9 ($\frac{33}{2}, \frac{31}{2}$) with the ${J}^{\ensuremath{\pi}}$ values in parentheses are proposed. Possible levels at 2474.2, 3064.9, and 3209.2 (${\frac{21}{2}}_{3}^{+}$) keV are also suggested. The measured angular distributions provided (i) branching ratios, (ii) ${J}^{\ensuremath{\pi}}$ assignments corroborated by deduced angular-distribution attenuation coefficients, level excitation functions, and side-feeding yields, and (iii) multipole mixing ratios $\ensuremath{\delta}(\frac{E2}{M1})$. Lifetimes for nine high-spin levels and limits for four additional ones were obtained by the Doppler-shift attenuation method from measurements with the $^{93}\mathrm{Nb}(\ensuremath{\alpha}, 2n)^{95}\mathrm{Tc}^{*}(\ensuremath{\gamma})$ reaction at 18.5, 20.6, 23.6, and 26.7 MeV. The lifetimes were extracted from singles spectra taken in the presence of standards at 7, 4, 7, and 8 angles, respectively, between 0\ifmmode^\circ\else\textdegree\fi{} and 90\ifmmode^\circ\else\textdegree\fi{} for the four bombardment energies by examining the dependence on ${E}_{\ensuremath{\alpha}}$ of the effective level lifetime. For many transitions $B(E2)$ and $B(M1)$ values were obtained. The present results are compared with calculations based on the coupling of three-quasiparticle ${({g}_{\frac{9}{2}})}^{3}$ configurations to the quadrupole vibrations of the core and remarkable agreement is observed for states up to only ${\frac{19}{2}}_{1}^{+}$. This model fails to explain the properties of the higher-spin states with ${J}^{\ensuremath{\pi}}>~{\frac{21}{2}}^{+}$.NUCLEAR REACTIONS $^{93}\mathrm{Nb}(\ensuremath{\alpha}, 2n)^{95}\mathrm{Tc}^{*}(\ensuremath{\gamma})$, $E=17\ensuremath{-}30$ MeV, monoisotopic targets. Measured ${E}_{\ensuremath{\gamma}}$, ${I}_{\ensuremath{\gamma}}$, ${I}_{\ensuremath{\gamma}}(\ensuremath{\theta})$, $\ensuremath{\sigma}(E)$, $\ensuremath{\Delta}{\overline{E}}_{\ensuremath{\gamma}}(E, \ensuremath{\tau})$, $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}$ coin, deduced $^{95}\mathrm{Tc}$ levels, $J$, $\ensuremath{\pi}$, branching ratios, $\ensuremath{\tau}$, $\ensuremath{\delta}(\frac{E2}{E1})$, $B(E2)$, and $B(M1)$ values; Ge(Li) detectors, Ge(Li)-NaI(Tl) anti-Compton spectrometer, 1.9 keV at 1332 keV.