Giant E 1 resonances in Be 8 from the reaction<mml:math xmlns:mml="http://www.…
1976; American Institute of Physics; Volume: 14; Issue: 1 Linguagem: Inglês
10.1103/physrevc.14.28
ISSN1538-4497
AutoresGeorge A. Fisher, P. Paul, F. Rieß, S. S. Hanna,
Tópico(s)Muon and positron interactions and applications
ResumoThe giant electric dipole resonances based on the ground state (${0}^{+}$) and first excited state (${2}^{+}$) of $^{8}\mathrm{Be}$ have been studied with the reactions $^{7}\mathrm{Li}(p,{\ensuremath{\gamma}}_{0})^{8}\mathrm{Be}$ and $^{7}\mathrm{Li}(p,{\ensuremath{\gamma}}_{1})^{8}\mathrm{Be}$ over the range ${E}_{p}=0.8 \mathrm{to} 17.6$ MeV. Both resonances show a simple resonant shape with little fine structure. The ${\ensuremath{\gamma}}_{1}$ giant resonance is displaced upward from the ${\ensuremath{\gamma}}_{0}$ resonance by an energy of 2.2 MeV which is approximately equal to the excitation of the ${2}^{+}$ state. The reduced ($\ensuremath{\gamma},{p}_{0}$) strengths of the two resonances are approximately equal and each exhausts about 10% of the $E1$ sum rule. The angular distributions for both ${\ensuremath{\gamma}}_{0}$ and ${\ensuremath{\gamma}}_{1}$ are quite constant over the giant resonance structure and are predominantly dipole in character. A simple model can be invoked to explain the dominant $E1$ features. The presence of ${P}_{1}(cos\ensuremath{\theta})$ and ${P}_{3}(cos\ensuremath{\theta})$ terms in both angular distributions indicates $E2$ strength which probably increases above the $E1$ resonances. Some parameters for the narrow levels at 18.15 and 19.06 MeV in $^{8}\mathrm{Be}$ are given.NUCLEAR REACTIONS $^{7}\mathrm{Li}(p,\ensuremath{\gamma})$, $E=0.8\ensuremath{-}17.6$ MeV; measured $\ensuremath{\sigma}(E;{E}_{\ensuremath{\gamma}},\ensuremath{\theta})$. Deduced properties $^{8}\mathrm{Be}$ levels at ${E}_{x}=18.15,19.06$ MeV and ${\ensuremath{\gamma}}_{0}$, ${\ensuremath{\gamma}}_{1}$ giant resonances. 99% enriched $^{7}\mathrm{Li}$ target.
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