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The β decays of N12 and B12 have been studied at KVI and JYFL to resolve the composition of the broad and interfering 0+ and 2 + strengths in the triple-α continuum. For the first time a complete treatment of 3α decay is presented including all major breakup channels. A multilevel, many-channel R-matrix formalism has been developed for the complete description of the breakup in combination with the recently published separate analysis of angular correlations. We find that, in addition to the Hoyle state at 7.65 MeV, more than one 0+ and 2+ state is needed to reproduce the spectra. Broad 03+ and 22+ states are found between 10.5 and 12 MeV in this work. The presence of β strength up to the N12 Q-value window suggests the presence of additional 0+ and 2 + components in the C12 structure at energies above 12.7 MeV. © 2010 The American Physical Society. ; Supported by the Academy of Finland (Project No. 44875), by the Spanish Agency CICYT (Nos. FPA2005-02379 and FPA2007-62216) and MEC Consolider Project No. CSD2007-00042, by the Belgian IAP P6/23 project and FWO-Vlaanderen, by the European Union sixth Framework Programme "EURONS"(No. 506065), and by the Swedish Research Council and the Knut and Alice Wallenberg Foundation. T.N. is a Royal Swedish Academy of Sciences Research Fellow supported by a grant from the Knut and Alice Wallenberg Foundation. The work at KVI was performed as part of Program 48 (TRIµP) of the Stichting voor Fundamenteel Onderzoek der Materie (FOM). ; Peer Reviewed

We have used the 10B(3He,p¿¿¿) reaction at 4.9 MeV and the 11B(3He,d¿¿¿) reaction at 8.5 MeV to determine the energy, width, and decay mechanism of resonances in 12C above the triple-¿ threshold up to 21 MeV in excitation energy. Comparison with various models has allowed us to estimate the degree of clustering of the states studied. © 2012 American Physical Society. ; Support by the Spanish Research Grant FPA2009-07387 and Consolider Project CSD2007-00042, by the European Union Sixth Framework through RII3- EURONS/ JRA4-DLEP (Contract No. 506065). Support of the CSIC I3P program cofinanced by the European Social Fund, and the support of the US Department of Energy, Office of Nuclear Physics, under Contract No. DE-AC02-06CH11357. O.S.K. Support from the Villum Kann Rasmussen Foundation. ; Peer Reviewed

6 pags., 4 figs., 2 tabs. -- PACS:27.20.+n25.55.Hp23.20.-g29.85.-c ; The reactions 10B (3He, p α α α) at 4.9 MeV and 11B (3He, d α α α) at 8.5 MeV have been used to investigate the γ decay of states in 12C. By measuring the four-body final state in complete kinematics we are able to detect γ transitions indirectly. We find γ transitions from the 15.11 MeV state in 12C to the 12.71, 11.83, 10.3 and 7.65 MeV states followed by their breakup into three α particles. The relative γ-ray branching ratios obtained are (1.2 ± 0.3), (0.32 ± 0.12), (1.4 ± 0.2) and (4.4 ± 0.8) %, respectively, with the remaining (92.7 ± 1.0) % of the γ decays going to the bound states. We obtain Γα / Γ = (2.8 ± 1.2) % for the isospin-forbidden α decay of the 15.11 MeV state. From the 12.71 MeV state we find γ transitions to the 10.3 and 7.65 MeV states. The relative γ-ray branching ratios are (0.9- 0.5 + 0.6) and (2.6- 1.2 + 1.6) %, respectively, with the remaining (96.6- 1.3 + 1.7) % of the γ decays going to the bound states. Finally, we discuss the relation between the β decay of 12N and 12B to states in 12C and the γ decay of the 15.11 MeV analog in 12C to the same states. © 2009 Elsevier B.V. ; We would like to acknowledge the support of the Spanish CICYT research grant FPA2007-62170 and the MICINN Consolider Project CSD 2007-00042 as well as the support of the European Union VI Framework through RII3-EURONS/JRA4-DLEP (contract number 506065). D.G. is a Juan de la Cierva fellow.

Absolute branching ratios to unbound states in C12 populated in the β decays of N12 and B12 are reported. Clean sources of N12 and B12 were obtained using the isotope separation on-line (ISOL) method. The relative branching ratios to the different populated states were extracted using single-alpha as well as complete kinematics triple-alpha spectra. These two largely independent methods give consistent results. Absolute normalization is achieved via the precisely known absolute branching ratio to the bound 4.44 MeV state in C12. The extracted branching ratios to the unbound states are a factor of three more precise than previous measurements. Branching ratios in the decay of Na20 are also extracted and used to check the results. © 2009 The American Physical Society. ; Supported by the Academy of Finland (Project No. 44875), by the Spanish Agency CICYT (Nos. FPA2007–62170 and FPA2007–62216), by the European Union Sixth Framework Programme "EURONS" (No. 506065), by the Swedish Research Council, and the Knut and Alice Wallenberg foundation. ; Peer Reviewed