UBC Theses and Dissertations

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UBC Theses and Dissertations

Carbon 12C(alpha, alpha) 12C*[i.e. Carbon 12 (alpha alpha prime) carbon 12] and 10B([alpha]d)12C* reactions to the T=0 12.71 mev and T=1 15.11 mev states in 12C Spuller, Joseph


The yields of the reactions 12C(α, α ')12C* to the T=0 state at 12.71 MeV (Jπ=1+ ) and the T=l state at 15.11 MeV (Jπ=1+ ) were measured by detecting the decay of these levels to the ground state by gamma emmission. A 90° (lab) yield curve from threshold to Eα= 27.0 MeV was obtained for each reaction. Both states have to be populated via an unnatural parity process and in addition the population of the 15.11 MeV level is isospin forbidden. Nevertheless, excitation of both levels is unambiguously detected. Although the ratio of the yields has a considerable energy dependence ( 1%<̲δ15.11/ δ 12.71<̲ 20%), conclusive evidence is shown for the breaking of isospin in l60*(Ex = 24.0 to 27.3 MeV). The 15.11 MeV yield curve had considerable structure, suggesting the formation of interimmediate states in 16₀* . While the yield of the 12.71 MeV gamma ray also showed evidence of structure, it was not as . dramatic as the 15.11 MeV gamma ray. The yield of the reaction 10B(a ,dy)12C* to the 12.71 and 15.11 levels was also measured. If the outgoing particle is a true deuteron and not an unbound n-p pair, the population of the i5.ll is isospin forbidden. Contrary to the 15.11 and 12.71 yields in 12C(a , a’)12C*f no resonant structure was found ln either the 12.71 or 15.11 yields; it is suggested that the reactions proceed through an isospin allowed sequence.

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