In the centres of stars where the temperature is high enough, three alpha-particles (helium nuclei) are able to combine to form 12C because of a resonant reaction leading to a nuclear excited state. (Stars with masses greater than approximately 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 Universe, and for determining the size of the iron core of a star just before it goes supernova, it has hitherto been insufficiently determined. Here we report a measurement of the inverse process, where a 12C nucleus decays to three alpha-particles. We find a dominant resonance at an energy of approximately 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-alpha rate for temperatures from 10(7) K to 10(10) K and find significant deviations from the standard rates. Our rate below approximately 5 x 10(7) 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 believed. At temperatures above 10(9) K, our rate is much less, which modifies predicted nucleosynthesis in supernovae.

Using decays of a clean source of 12 N produced at the IGISOL facility, we have measured the breakup of the 12 C (12.71 MeV) state into three particles with a segmented particle detector setup. The high quality of the data permits solving the question of the breakup mechanism of the 12.71 MeV state, a longstanding problem in few-body nuclear physics. Among existing models, a modified sequential model fits the data best, but systematic deviations indicate that a three-body description is needed.

Decay properties of neutron-deficient exotic nuclei close to A = 80 have been investigated at the IGISOL facility. The studied nuclei, 81 Y, 81 Sr, 81m Kr, 85 Nb, 85 Zr, 86 Mo and 86 Nb, were produced by a 32 S beam from the Jyväskylä isochronous cyclotron on 54 Fe and nat Ni targets. The internal conversion coefficient for a 190.5 keV isomeric transition in 81m Kr has been measured and the internal transition rate has been determined. The internal transition rate has been used to estimate a neutrino capture rate on 81 Br, which yields a log ft of 5.13 ± 0.09 for the reaction 81 Br(ν, e −) 81m Kr. A new isomer with a half-life of 3.3 ± 0.9 s has been observed in 85 Nb. The existence of an earlier reported isomer with a half-life of 56 s in 86 Nb has not been confirmed.

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