Structure ofTc94

Abstract

The level structure and decay properties of levels in $^{94}\mathrm{Tc}$ up to 2307 keV of excitation have been investigated via measurements of excitation functions of singles $\ensuremath{\gamma}$ rays and via $n\ensuremath{\gamma}$- and $\ensuremath{\gamma}\ensuremath{\gamma}$-coincidence experiments following the $^{94}\mathrm{Mo}$ ($p$,$n\ensuremath{\gamma}$) reaction with proton energies between 5.0 and 8.0 MeV. From these experiments and from high resolution singles energy and directional-correlation measurements an extended decay scheme has been obtained which included 42 levels in $^{94}\mathrm{Tc}$ and incorporated 180 $\ensuremath{\gamma}$ rays. New levels at 797.9 (${2}^{\ensuremath{-}}$), 823.2(${2}^{+}$), 917.7(${3}^{+}$), 926.3(${4}^{+}$), 953.5(${3}^{\ensuremath{-}}$), 1045.1(${2}^{+}$), 1178.4(${2}^{\ensuremath{-}}$,${3}^{\ensuremath{-}}$), 1263.9(${3}^{+}$), 1314.1(${4}^{(\ensuremath{-})}$), 1351.7(${3}^{\ensuremath{-}}$), 1364.9(${2}^{+}$), 1394.2(${3}^{\ensuremath{-}}$), 1406.8(${3}^{+}$), 1429.3(${1}^{+}$), 1540.0(${3}^{+}$), 1659.9, 1679.0, 1778.4, 1856.8, 1865.2, 1884.0, 1973.5, 2002.1, 2094.4, 2131.8, 2167.0, 2208.2, 2213.5, 2241.6, 2264.4, 2267.8, and 2306.6 keV with the assigned ${J}^{\ensuremath{\pi}}$ values in parentheses were postulated. The singles directional correlations for many transitions provided (i) reliable branching ratios, (ii) ${J}^{\ensuremath{\pi}}$ assignments, and (iii) multipole mixing ratios from analysis of the correlations via the compound statistical theory for nuclear reactions. Lifetimes for 18 states in $^{94}\mathrm{Tc}$ were obtained by the Doppler-shift-attenuation method via the $^{94}\mathrm{Mo}$($p$,$n\ensuremath{\gamma}$) reaction at 7.2 MeV. The lifetimes were extracted from singles spectra taken in the presence of standards at eight angles between 0\ifmmode^\circ\else\textdegree\fi{} and 110\ifmmode^\circ\else\textdegree\fi{} to the beam direction by employing a centroid shift analysis of the data. For a good number of transitions in $^{94}\mathrm{Tc}$ values or limits for $B(E1)$, $B(E2)$, and $B(M1)$ were obtained. The positive-parity levels up to 1.711 MeV of excitation and their decay properties were calculated in the shell-model framework and are compared with the corresponding experimental quantities.NUCLEAR REACTIONS $^{94}\mathrm{Mo}$($p$,$n\ensuremath{\gamma}$) $^{94}\mathrm{Tc}$, ${E}_{p}=5.0\ensuremath{-}8.0$ MeV, enriched targets. Measured ${E}_{\ensuremath{\gamma}}$, ${I}_{\ensuremath{\gamma}}$, ${I}_{\ensuremath{\gamma}}(\ensuremath{\theta})$, $\ensuremath{\sigma}(\mathrm{Ep})$, $\ensuremath{\Delta}E\ensuremath{\gamma}(\ensuremath{\tau})$, $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}$ coin, $n\ensuremath{-}\ensuremath{\gamma}$ coin, deduced $^{94}\mathrm{Tc}$ levels, thresholds, branching ratios, $\ensuremath{\tau}$, $\ensuremath{\delta}(\frac{E2}{M1})$, $B(E2)$, $B(M1)$, and $B(E1)$ values, Ge(Li) detectors, NE-213 scintillator detector. Calculated $^{94}\mathrm{Tc}$ positive-parity levels, $B(E2)$, $B(M1)$, $\ensuremath{\tau}$, and branching ratios.