| 1. |
- Hyldegaard, S., et al.
(författare)
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R-matrix analysis of the beta decays of 12N and 12B
- 2010
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Ingår i: Physical Review C - Nuclear Physics. - 2469-9985 .- 2469-9993. ; 81:2
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Tidskriftsartikel (refereegranskat)abstract
- The β decays of 12N and 12B 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 12N Q-value window suggests the presence of additional 0+ and 2+ components in the 12C structure at energies above 12.7 MeV.
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| 2. |
- Roger, T., et al.
(författare)
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Precise Determination of the Unperturbed B8 Neutrino Spectrum
- 2012
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Ingår i: Phys. Rev. Lett.. ; 108:16, s. Art. no. 162502-
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Tidskriftsartikel (refereegranskat)abstract
- A measurement of the final state distribution of the 8B beta decay, obtained by implanting a 8B beam in a double-sided silicon strip detector, is reported here. The present spectrum is consistent with a recent independent precise measurement performed by our collaboration at the IGISOL facility, Jyvaskyla [O. S.Kirsebom et al., Phys. Rev. C 83, 065802 (2011)]. It shows discrepancies with previously measuredspectra, leading to differences in the derived neutrino spectrum. Thanks to a low detection threshold, theneutrino spectrum is for the first time directly extracted from the measured final state distribution, thusavoiding the uncertainties related to the extrapolation of R-matrix fits. Combined with the IGISOL data,this leads to an improvement of the overall errors and the extension of the neutrino spectrum at highenergy. The new unperturbed neutrino spectrum represents a benchmark for future measurements of thesolar neutrino flux as a function of energy.
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| 3. |
- Kirsebom, O. S., et al.
(författare)
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Precise and accurate determination of the B-8 decay spectrum
- 2011
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Ingår i: Physical Review C - Nuclear Physics. - 2469-9985 .- 2469-9993. ; 83:6
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Tidskriftsartikel (refereegranskat)abstract
- Accurate measurements of the B-8 neutrino spectrum are important for the interpretation of solar neutrino data. Experimentally, the B-8 neutrino spectrum can be obtained from the measurement of the beta-delayed alpha spectrum. We report on an alpha-alpha coincidence measurement performed at the IGISOL facility in Jyvaskyla, Finland. Our measurement allows extensive cross-checks to be performed and gives a more intense neutrino spectrum at high energies compared to the present standard. The deviation reaches 4% at the end point of the spectrum. Below 11 MeV, the deviation is less than 1%.
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| 4. |
- Alcorta, M., et al.
(författare)
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Properties of resonances in 12C above the triple-alpha threshold
- 2011
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Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 312:SECTION 9, s. Art. no. 092013-
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Konferensbidrag (refereegranskat)abstract
- A complete kinematics study of the 10B(3He, pααα) and the 11B(3He, dααα) reactions has been performed to study the multi-particle break-up of 12C resonances above the triple-alpha threshold. The values of energy and widths of some states has been improved, and in states of natural parity partial branches of decay through the ground state of 8Be have been extracted. The influence of the "ghost" of the 8Be ground state has been taken into account in order to clarify the partial branches.
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| 5. |
- Kirsebom, O. S., et al.
(författare)
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Breakup of 12C resonances into three α particles
- 2010
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Ingår i: Physical Review C - Nuclear Physics. - 2469-9985 .- 2469-9993. ; 81:6
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Tidskriftsartikel (refereegranskat)abstract
- The reaction He-3 + B-11 -> d + C-12* has been used to populate resonances in C-12 up to an excitation energy of 15 MeV. The subsequent breakup to three alpha particles has been measured in complete kinematics. Dalitz plots are used to visualize and analyze the data. The Dalitz plot intensity distribution exhibits zero points characteristic of the total spin and parity of the 3 alpha system allowing us to determine the spin and parity of a state in C-12 at 13.35 MeV whose quantum numbers were hitherto not well established. The Dalitz plot intensity distributions of the 2(-) state at 11.83 MeV and the 1(+) state at 12.71 MeV are compared with the predictions of a recent three-body calculation as well as with simpler models. All are able to reproduce the gross structures seen in the Dalitz plot, but none give an accurate description of the detailed profile of the distributions.
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| 6. |
- Kirsebom, O. S., et al.
(författare)
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The 8B neutrino spectrum
- 2010
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Ingår i: 11th Symposium on Nuclei in the Cosmos, NIC 2010; Heidelberg; Germany; 19 July 2010 through 23 July 2010. - 1824-8039.
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Konferensbidrag (refereegranskat)abstract
- Knowledge of the energy spectrum of the neutrinos emitted in the β decay of8B in the Sun is needed to interpret the neutrino spectrum measured on Earth. Experimentally, the 8B neutrino spectrum may be αextracted from the measurement of the β -delayed a spectrum. In this contribution, the results of a recent α-α coincidence measurement are presented and compared to previous measurements. The implications for the neutrino spectrum are clarified.
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| 7. |
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| 8. |
- Borge, M. J. G., et al.
(författare)
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Rare beta p decays in light nuclei
- 2013
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Ingår i: Journal of Physics G: Nuclear and Particle Physics. - : IOP Publishing. - 0954-3899 .- 1361-6471. ; 40:3, s. art.no. 035109-
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Tidskriftsartikel (refereegranskat)abstract
- Beta-delayed proton emission may occur at very low rates in the decays of the light nuclei Be-11 and B-8. This paper explores the potential physical significance of such decays, estimates their rates and reports on first attempts to detect them: an experiment at ISOLDE/CERN gives a branching ratio for Be-11 of ( 2.5 +/- 2.5) x 10(-6) and an experiment at JYFL a 95% confidence upper limit of 2.6 x 10(-5) for B-8.
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| 9. |
- Kirsebom, O. S., et al.
(författare)
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Improved Limit on Direct α Decay of the Hoyle State
- 2012
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Ingår i: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 108:20, s. 202501-
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Tidskriftsartikel (refereegranskat)abstract
- The current evaluation of the triple-α reaction rate assumes that the α decay of the 7.65 MeV, 0+ state in 12C, commonly known as the Hoyle state, proceeds sequentially via the ground state of 8Be. This assumption is challenged by the recent identification of two direct α-decay branches with a combined branching ratio of 17(5)%. If correct, this would imply a corresponding reduction in the triple-α reaction rate with important astrophysical consequences. We have used the 11B(3He,d) reaction to populate the Hoyle state and measured the decay to three α particles in complete kinematics. We find no evidence for direct α-decay branches, and hence our data do not support a revision of the triple-α reaction rate. We obtain an upper limit of 5×10-3 on the direct α decay of the Hoyle state at 95% C.L., which is 1 order of magnitude better than a previous upper limit.
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| 10. |
- Tengblad, Olof, 1957, et al.
(författare)
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12C formation: A classical quest in new light
- 2011
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Ingår i: AIP Conference Proceedings. - : AIP. - 1551-7616 .- 0094-243X. - 9780735409378 ; 1377, s. 270-274
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Konferensbidrag (refereegranskat)abstract
- In this work we have studied the break‐up of 12C following the reactions 10B(3He,pααα) and 11B(3He,dααα). The study was performed at the 5 MV tandem in Madrid. The break‐up gives us information on excited states in 12C from the famous Hoyle state up to an energy of almost 18 MeV. Using a highly segmented experimental set‐up the simultaneous detection of the three alpha particles in coincidence with a proton or deuteron respectively made possible a full kinematic reconstruction of the break‐up. On the basis of the energies of the 3 α particles and their angular correlations it has been possible to determine the spin and parity of states for cases in which the assignment has been doubtful. Some of these levels will also de‐excite via electromagnetic emission. The comparison between the energy of proton that populate a state of 12C and the sum of the energies of the 3α emitted from the same state makes possible to determine the presence of electromagnetic disintegration (γ) to lower states within 12C followed by the 3α break‐up.
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