1. Department of Physics and Astronomy, University of Aarhus, 8000 Århus C, Denmark
2. CERN, CH-1211 Geneva 23, Switzerland
3. Instituto Estructura de la Materia, CSIC, Serrano 113bis, E-28006, Madrid, Spain
4. KVI, Zernikelaan, 9747 AA Groningen, The Netherlands
5. Department of Physics, University of York, Heslington, YO10 5DD, UK
6. Department of Physics, University of Jyväskylä, FIN-40351 Jyväskylä, Finland
7. Helsinki Institute of Physics, FIN-00014 University of Helsinki, Finland
8. Experimental Physics, Chalmers University of Technology and Göteborg University, S-41296 Göteborg, Sweden

Correspondence to: Hans O. U. Fynbo¹ Correspondence and requests for materials should be addressed to H.F. (Email: fynbo@phys.au.dk).

Abstract

In the centres of stars where the temperature is high enough, three -particles (helium nuclei) are able to combine to form ¹²C because of a resonant reaction leading to a nuclear excited state¹. (Stars with masses greater than 0.5 times that of the Sun will at some point in their lives have a central temperature high enough for this reaction to proceed.) Although the reaction rate is of critical significance for determining elemental abundances in the Universe¹, and for determining the size of the iron core of a star just before it goes supernova², it has hitherto been insufficiently determined². Here we report a measurement of the inverse process, where a ¹²C nucleus decays to three -particles. We find a dominant resonance at an energy of 11 MeV, but do not confirm the presence of a resonance at 9.1 MeV (ref. 3). We show that interference between two resonances has important effects on our measured spectrum. Using these data, we calculate the triple- rate for temperatures from 10⁷ K to 10¹⁰ K and find significant deviations from the standard rates³. Our rate below 5 10⁷ K is higher than the previous standard, implying that the critical amounts of carbon that catalysed hydrogen burning in the first stars are produced twice as fast as previously believed⁴. At temperatures above 10⁹ K, our rate is much less, which modifies predicted nucleosynthesis in supernovae^{5, 6}.

1. Department of Physics and Astronomy, University of Aarhus, 8000 Århus C, Denmark
2. CERN, CH-1211 Geneva 23, Switzerland
3. Instituto Estructura de la Materia, CSIC, Serrano 113bis, E-28006, Madrid, Spain
4. KVI, Zernikelaan, 9747 AA Groningen, The Netherlands
5. Department of Physics, University of York, Heslington, YO10 5DD, UK
6. Department of Physics, University of Jyväskylä, FIN-40351 Jyväskylä, Finland
7. Helsinki Institute of Physics, FIN-00014 University of Helsinki, Finland
8. Experimental Physics, Chalmers University of Technology and Göteborg University, S-41296 Göteborg, Sweden

Correspondence to: Hans O. U. Fynbo¹ Correspondence and requests for materials should be addressed to H.F. (Email: fynbo@phys.au.dk).

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