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Nuclear Structure of Na 22 .I. Gamma-Ray Correlations and Lifetime Measurements for Levels of E ex </…

1967; American Institute of Physics; Volume: 160; Issue: 4 Linguagem: Inglês

10.1103/physrev.160.938

1536-6065

E. K. Warburton, J. W. Olness, A. R. Poletti,

Nuclear Physics and Applications

Levels of ${\mathrm{Na}}^{22}$ below an excitation energy of 3.1 MeV have been investigated through the ${\mathrm{F}}^{19}(\ensuremath{\alpha}, n\ensuremath{\gamma}){\mathrm{Na}}^{22}$ and ${\mathrm{Ne}}^{20}({\mathrm{He}}^{3}, p\ensuremath{\gamma}){\mathrm{Na}}^{22}$ reactions. Gamma-ray spectra from the first reaction were recorded with an 8-cc Ge(Li) detector at 90\ifmmode^\circ\else\textdegree\fi{}, 0\ifmmode^\circ\else\textdegree\fi{}, and 166\ifmmode^\circ\else\textdegree\fi{} to the $\ensuremath{\alpha}$ beam using Ca${\mathrm{F}}_{2}$ targets and $\ensuremath{\alpha}$ energies between 4.0 and 7.0 MeV. Spectra were similarly recorded at 90\ifmmode^\circ\else\textdegree\fi{} for ${E}_{{\mathrm{He}}^{3}}=5.65$ MeV in the second reaction. These studies were supplemented by $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}$ coincidence measurements with both NaI(Tl)-NaI(Tl) and NaI(Tl)-Ge(Li) $\ensuremath{\gamma}$-ray detector combinations. Gamma-ray angular distributions were measured at ${E}_{\ensuremath{\alpha}}=5.48$ MeV using the ${\mathrm{F}}^{19}(\ensuremath{\alpha}, n){\mathrm{Na}}^{22}$ reaction and $p\ensuremath{-}\ensuremath{\gamma}$ angular correlations were measured at ${E}_{{\mathrm{He}}^{3}}=5.65$ MeV using the ${\mathrm{Ne}}^{20}({\mathrm{He}}^{3}, p){\mathrm{Na}}^{22}$ reaction. From these measurements excitation energies and $\ensuremath{\gamma}$-ray decay modes were determined for the levels below 3.1-MeV excitation, information on spin-parity and isotopic-spin assignments was obtained, and values or limits for the mean lifetimes of the levels were extracted from observations of the $\ensuremath{\gamma}$-ray Doppler shifts. An isotopic-spin assignment of $T=1$ was made to the ${\mathrm{Na}}^{22}$ 1.952-MeV level; all other levels in the range $0.7<{E}_{x}(\mathrm{MeV}) 8), 1.528 (${3}^{+}$, ${5}^{+}$; 3.8\ifmmode\pm\else\textpm\fi{}0.9), 1.937 (${1}^{+}$; 0.06), 1.952 (1, 2; 0.09), 1.984 (${2}^{+}$, ${3}^{+}$; 1.6\ifmmode\pm\else\textpm\fi{}0.34), 2.211 (1; >11), 2.572 (\ensuremath{\le}3; >10), 2.969 (\ensuremath{\le}3; 0.14), 3.059 (\ensuremath{\le}3; 0.09). The combined influence of Doppler effects and the lifetimes of the initial states on the shapes of the full-energy-loss peaks of the 1.528 \ensuremath{\rightarrow} 0 and 1.984 \ensuremath{\rightarrow} 0.583 transitions is quite marked. The analysis of these shapes to obtain the lifetimes given above is described in detail. Some incidental information concerning excitation energies and lifetimes of energy levels in ${\mathrm{F}}^{19}$ and ${\mathrm{Ne}}^{22}$ is given in an Appendix.