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Properties of the 4.77- and 5.16-MeV States of B 10

1966; American Institute of Physics; Volume: 143; Issue: 3 Linguagem: Inglês

10.1103/physrev.143.692

1536-6065

D. E. Alburger, P. D. Parker, D. J. Bredin, D. H. Wilkinson, P. F. Donovan, A. Gallmann, R.E. Pixley, L. F. Chase, R. E. McDonald,

Nuclear Physics and Applications

The energy levels in ${\mathrm{B}}^{10}$ at 4.77 and 5.16 MeV have been studied by means of the reactions ${\mathrm{B}}^{11}({\mathrm{He}}^{3},\ensuremath{\alpha}){\mathrm{B}}^{10}$ and ${\mathrm{Li}}^{6}(\ensuremath{\alpha},\ensuremath{\gamma}){\mathrm{B}}^{10}$. In measurements on the ${\mathrm{B}}^{11}({\mathrm{He}}^{3},\ensuremath{\alpha}){\mathrm{B}}^{10}$ reaction (${{E}_{\mathrm{He}}}^{3}=3.5$ MeV), alpha particles populating states of ${\mathrm{B}}^{10}$ were observed at 90\ifmmode^\circ\else\textdegree\fi{} in coincidence with (a) ${\mathrm{B}}^{10}$ recoil nuclei, (b) ${\mathrm{B}}^{10}$ recoils and gamma rays, and (c) decay alpha particles, by using two solid-state detectors and a NaI detector. Relative alpha-particle and gamma-ray branching intensities were determined for the decay of the 4.77- and 5.16-MeV states. The ratio of population intensities of the 5.16- and 5.11-MeV states was measured by using a Buechner-type magnetic spectrograph. In the ${\mathrm{Li}}^{6}(\ensuremath{\alpha},\ensuremath{\gamma}){\mathrm{B}}^{10}$ reaction thick-target gamma-ray yields were measured at resonances for forming the 4.77- and 5.16-MeV states. For the 4.77-MeV state the angular distribution of the predominant 4.05-MeV gamma ray was determined, the 4.77-MeV ground-state transition was detected, and the angular distribution of the 4.77-MeV gamma ray was measured. The intensity of the ground-state gamma-ray branch from the 4.77-MeV level was measured to be (0.5\ifmmode\pm\else\textpm\fi{}0.1)%, and the angular distribution of this transition in the ${\mathrm{Li}}^{6}(\ensuremath{\alpha},\ensuremath{\gamma}){\mathrm{B}}^{10}$ reaction favors an assignment of ${J}^{\ensuremath{\pi}}={3}^{+}$ to the 4.77-MeV state. Assignments of either ${J}^{\ensuremath{\pi}}={2}^{+} or {3}^{+}$ are allowed by the angular distribution of the 4.05-MeV transition from this state. $\frac{{\ensuremath{\Gamma}}_{\ensuremath{\gamma}}}{\ensuremath{\Gamma}}$ for the 4.77-MeV level was measured to be (2.3\ifmmode\pm\else\textpm\fi{}0.3)\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}3}$. For the ${J}^{\ensuremath{\pi}}={3}^{+}$ assignment, partial widths for the 4.77-MeV level were measured to be ${\ensuremath{\Gamma}}_{\ensuremath{\gamma}}=0.033\ifmmode\pm\else\textpm\fi{}0.006$ eV and ${\ensuremath{\Gamma}}_{\ensuremath{\alpha}}=14\ifmmode\pm\else\textpm\fi{}3$ eV. The partial widths of the 5.16-MeV level were measured as ${\ensuremath{\Gamma}}_{\ensuremath{\gamma}}=2.9\ifmmode\pm\else\textpm\fi{}1.1$ eV and ${\ensuremath{\Gamma}}_{\ensuremath{\alpha}}=0.44\ifmmode\pm\else\textpm\fi{}0.09$ eV for an alpha-particle branch of (13\ifmmode\pm\else\textpm\fi{}4)%. The properties of these and neighboring states are discussed in terms of the independent-particle model. Good agreement is found on some striking features but several points remain to be clarified.