Nuclear Structure ofNa22.I. Gamma-Ray Correlations and Lifetime Measurements for Levels ofEex<3.1MeV

Abstract

Levels of ${\mathrm{Na}}^{22}$ below an excitation energy of 3.1 MeV have been investigated through the ${\mathrm{F}}^{19}(\alpha , n\gamma ){\mathrm{Na}}^{22}$ and ${\mathrm{Ne}}^{20}({\mathrm{He}}^3, p\gamma ){\mathrm{Na}}^{22}$ reactions. Gamma-ray spectra from the first reaction were recorded with an 8-cc Ge(Li) detector at 90°, 0°, and 166° to the $\alpha$ beam using Ca${\mathrm{F}}_2$ targets and $\alpha$ energies between 4.0 and 7.0 MeV. Spectra were similarly recorded at 90° for $E_{{\mathrm{He}}^3}=5.65\mathrm{}$ MeV in the second reaction. These studies were supplemented by $\gamma -\gamma$ coincidence measurements with both NaI(Tl)-NaI(Tl) and NaI(Tl)-Ge(Li) $\gamma$-ray detector combinations. Gamma-ray angular distributions were measured at $E_{\alpha }=5.48\mathrm{}$ MeV using the ${\mathrm{F}}^{19}(\alpha , n){\mathrm{Na}}^{22}$ reaction and $p-\gamma$ angular correlations were measured at $E_{{\mathrm{He}}^3}=5.65\mathrm{}$ MeV using the ${\mathrm{Ne}}^{20}({\mathrm{He}}^3, p){\mathrm{Na}}^{22}$ reaction. From these measurements excitation energies and $\gamma$-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 $\gamma$-ray Doppler shifts. An isotopic-spin assignment of $T=1\mathrm{}$ was made to the ${\mathrm{Na}}^{22}$ 1.952-MeV level; all other levels in the range $0.7<\mathrm{}{E}_x\left(\mathrm{MeV}\right)<\mathrm{}3.1\mathrm{}$ were assigned $T=0\mathrm{}$. Upon combining our results with previously available information, we deduce the following spin-parity and lifetime information $\left\{E_{\mathrm{ex}}\right(\mathrm{MeV}\left)\right[J^{\pi }; {\tau }_m\left(\mathrm{psec}\right)\left]\right\}$ for the third through eleventh levels of ${\mathrm{Na}}^{22}$: 0.891 ($4^{+}$; >8), 1.528 (

Keywords

• GAMMA RAY
• NA22 REACTION
• EXCITATION
• SPIN
• MEV
• NAI
• Γ RAY

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