| 1. |
- Alcorta, M., et al.
(författare)
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Nuclear Structure of C-12 from Break-up Studies in Complete Kinematics
- 2009
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Ingår i: AIP Conference Proceedings. - : AIP. - 1551-7616 .- 0094-243X. - 9780735407022 ; 1165, s. 27-30 461
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Konferensbidrag (refereegranskat)abstract
- A complete kinematics study of the B-10(He-3,p alpha alpha alpha) and B-11(He-3,d alpha alpha alpha) reactions has been performed to study the multi-particle break-up of C-12 resonances above the triple-alpha threshold. Four-particle coincidence detection gives us complete information on the direction and energy of the individual alpha particles from the decay of C-12, allowing us to extract new information on the structure of C-12 which we shall present in this contribution. We have observed gamma de-excitation of the T=1 15.11 MeV resonance using charged particle detectors, and have constructed Dalitz plots of the individual resonances in C-12 using the complete kinematics information of the alpha particles which come from their break-up.
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| 2. |
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| 3. |
- 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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| 4. |
- Borge, M. J. G., et al.
(författare)
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Mapping of the C-12* states via the B-10(He-3,p alpha alpha alpha) reaction
- 2007
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Ingår i: European Physical Journal: Special Topics. - : Springer Science and Business Media LLC. - 1951-6401 .- 1951-6355. ; 150:1, s. 207-210
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Tidskriftsartikel (refereegranskat)abstract
- We have studied C-12 in full kinematics via the B-10(He-3, p alpha alpha alpha) reaction at an energy of 2.45 MeV. In our data we have identified states in C-12 from the ground state up to about 18 MeV, with spins ranging from 0 to 4. Due to the very good resolution, we are able to determine properties of these C-12 resonances, such as their energy, width, and spin. In this contribution preliminary results from the ongoing analysis are presented. Main focus on the precise determination of the breakup spectra for all resonances.
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| 5. |
- Fynbo, H. O. U., et al.
(författare)
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The β-decay approach for studying 12C
- 2008
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Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 111:1
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Tidskriftsartikel (refereegranskat)abstract
- The β-decays of the mirror nuclei 12B and 12N both populate states in 12C and they are therefore a precious source of information about this nucleus. Due to the selection rules of β-decay only 0+, 1+ and 2+ states are populated. This allows a very clean study of unbound states just above the 3α-threshold with those spin and parities. This probe has been applied in two experiments using two complementary experimental techniques: in the first the three α-particles emitted after β-decay are measured in coincidence in separate detectors using the ISOL method, while in the second method 12B and 12N are implanted in a detector and the summed energy of the three α-particles is measured directly. Preliminary results from the two approaches are presented. © 2008 IOP Publishing Ltd.
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| 6. |
- Hyldegaard, S., et al.
(författare)
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Precise branching ratios to unbound 12C states from 12N and 12B [beta]-decays
- 2009
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Ingår i: Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 678:5, s. 459 - 464
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Tidskriftsartikel (refereegranskat)abstract
- Two complementary experimental techniques have been used to extract precise branching ratios to unbound states in 12C from 12N and 12B [beta]-decays. In the first the three [alpha]-particles emitted after [beta]-decay are measured in coincidence in separate detectors, while in the second method 12N and 12B are implanted in a detector and the summed energy of the three [alpha]-particles is measured directly. For the narrow states at 7.654 MeV (0+) and 12.71 MeV (1+) the resulting branching ratios are both smaller than previous measurements by a factor of [similar, equals]2. The experimental results are compared to no-core shell model calculations with realistic interactions from chiral perturbation theory, and inclusion of three-nucleon forces is found to give improved agreement.
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| 7. |
- 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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| 8. |
- Hyldegaard, S., et al.
(författare)
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STUDIES OF C-12 USING beta-DECAYS
- 2008
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Ingår i: International Journal of Modern Physics E. - 0218-3013. ; 17:10, s. 2182-2187
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Konferensbidrag (refereegranskat)abstract
- The nuclear structure of states in C-12 have been a subject of interest for both theory and experiment since the early days of nuclear physics. Many open questions remain, especially concerning the existence and properties of 0(+) and 2(+) states in the triple alpha continuum. A series of experiments have been performed using beta-decay of N-12 and B-12 to probe these states. The latest experiment was performed at KVI using an implantation method, measuring the sum energy of the three alpha-particles directly. Preliminary results from this experiment will be presented.
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| 9. |
- 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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| 10. |
- 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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