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Sökning: WFRF:(Kirsebom O. S.)

  • Resultat 1-22 av 22
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1.
  • Hyldegaard, S., et al. (författare)
  • R-matrix analysis of the beta decays of 12N and 12B
  • 2010
  • Ingår i: Physical Review C - Nuclear Physics. - 2469-9985 .- 2469-9993. ; 81:2
  • 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)
  • Precise Determination of the Unperturbed B8 Neutrino Spectrum
  • 2012
  • Ingår i: Phys. Rev. Lett.. ; 108:16, s. Art. no. 162502-
  • 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.
  • Fynbo, H. O. U., et al. (författare)
  • The β-decay approach for studying 12C
  • 2008
  • Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 111:1
  • 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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4.
  • Hyldegaard, S., et al. (författare)
  • Precise branching ratios to unbound 12C states from 12N and 12B [beta]-decays
  • 2009
  • Ingår i: Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 678:5, s. 459 - 464
  • 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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5.
  • Kirsebom, O. S., et al. (författare)
  • Measurement of the 2+→0+ ground-state transition in the β decay of F 20
  • 2019
  • Ingår i: Physical Review C. - 2469-9985. ; 100:6
  • Tidskriftsartikel (refereegranskat)abstract
    • We report the first detection of the second-forbidden, nonunique, 2+→0+, ground-state transition in the β decay of F20. A low-energy, mass-separated F+20 beam produced at the IGISOL facility in Jyväskylä, Finland, was implanted in a thin carbon foil and the β spectrum measured using a magnetic transporter and a plastic-scintillator detector. The β-decay branching ratio inferred from the measurement is bβ=[0.41±0.08(stat)±0.07(sys)]×10-5 corresponding to logft=10.89(11), making this one of the strongest second-forbidden, nonunique β transitions ever measured. The experimental result is supported by shell-model calculations and has significant implications for the final evolution of stars that develop degenerate oxygen-neon cores. Using the new experimental data, we argue that the astrophysical electron-capture rate on Ne20 is now known to within better than 25% at the relevant temperatures and densities.
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6.
  • Kirsebom, O. S., et al. (författare)
  • Precise and accurate determination of the B-8 decay spectrum
  • 2011
  • Ingår i: Physical Review C - Nuclear Physics. - 2469-9985 .- 2469-9993. ; 83:6
  • 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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7.
  • IDS Collaboration, HASH(0x3dac240), et al. (författare)
  • Beta-delayed proton emission from 20Mg
  • 2016
  • Ingår i: European Physical Journal A. - : Springer Science and Business Media LLC. - 1434-601X .- 1434-6001. ; 52:10, s. 304-
  • Tidskriftsartikel (refereegranskat)abstract
    • Beta-delayed proton emission from 20 Mg has been measured at ISOLDE, CERN, with the ISOLDE Decay Station (IDS) setup including both charged-particle and gamma-ray detection capabilities. A total of 27 delayed proton branches were measured including seven so far unobserved. An updated decay scheme, including three new resonances above the proton separation energy in 20 Na and more precise resonance energies, is presented. Beta-decay feeding to two resonances above the Isobaric Analogue State (IAS) in 20 Na is observed. This may allow studies of the 4032.9(2.4)keV resonance in 19 Ne through the beta decay of 20 Mg, which is important for the astrophysically relevant reaction 15O(?,?)19Ne. Beta-delayed protons were used to obtain a more precise value for the half-life of 20 Mg, 91.4(1.0)ms.
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8.
  • Jensen, E. A.M., et al. (författare)
  • Detailed study of the decay of 21Mg
  • 2024
  • Ingår i: European Physical Journal A. - 1434-601X .- 1434-6001. ; 60:7
  • Tidskriftsartikel (refereegranskat)abstract
    • Beta-delayed proton and gamma emission in the decay of 21Mg has been measured at ISOLDE, CERN with the ISOLDE Decay Station (IDS) set-up. The existing decay scheme is updated, in particular what concerns proton transitions to excited states in 20Ne. Signatures of interference in several parts of the spectrum are used to settle spin and parity assignments to highly excited states in 21Na. The previously reported βpα branch is confirmed. A half-life of 120.5(4) ms is extracted for 21Mg. The revised decay scheme is employed to test mirror symmetry in the decay and to extract the beta strength distribution of 21Mg that is compared with theory.
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9.
  • Kirsebom, O. S., et al. (författare)
  • Discovery of an Exceptionally Strong β -Decay Transition of F 20 and Implications for the Fate of Intermediate-Mass Stars
  • 2019
  • Ingår i: Physical Review Letters. - 0031-9007. ; 123:26
  • Tidskriftsartikel (refereegranskat)abstract
    • A significant fraction of stars between 7 and 11 solar masses are thought to become supernovae, but the explosion mechanism is unclear. The answer depends critically on the rate of electron capture on Ne20 in the degenerate oxygen-neon stellar core. However, because of the unknown strength of the transition between the ground states of Ne20 and F20, it has not previously been possible to fully constrain the rate. By measuring the transition, we establish that its strength is exceptionally large and that it enhances the capture rate by several orders of magnitude. This has a decisive impact on the evolution of the core, increasing the likelihood that the star is (partially) disrupted by a thermonuclear explosion rather than collapsing to form a neutron star. Importantly, our measurement resolves the last remaining nuclear physics uncertainty in the final evolution of degenerate oxygen-neon stellar cores, allowing future studies to address the critical role of convection, which at present is poorly understood
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10.
  • Alcorta, M., et al. (författare)
  • Properties of resonances in 12C above the triple-alpha threshold
  • 2011
  • Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 312:SECTION 9, s. Art. no. 092013-
  • 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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11.
  • Kirsebom, O. S., et al. (författare)
  • Breakup of 12C resonances into three α particles
  • 2010
  • Ingår i: Physical Review C - Nuclear Physics. - 2469-9985 .- 2469-9993. ; 81:6
  • 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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12.
  • Kirsebom, O. S., et al. (författare)
  • First Accurate Normalization of the β -delayed α Decay of N 16 and Implications for the C 12 (α,γ) O 16 Astrophysical Reaction Rate
  • 2018
  • Ingår i: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 121:14
  • Tidskriftsartikel (refereegranskat)abstract
    • Published by the American Physical Society. The C12(α,γ)O16 reaction plays a central role in astrophysics, but its cross section at energies relevant for astrophysical applications is only poorly constrained by laboratory data. The reduced α width, γ11, of the bound 1- level in O16 is particularly important to determine the cross section. The magnitude of γ11 is determined via sub-Coulomb α-transfer reactions or the β-delayed α decay of N16, but the latter approach is presently hampered by the lack of sufficiently precise data on the β-decay branching ratios. Here we report improved branching ratios for the bound 1- level [bβ,11=(5.02±0.10)×10-2] and for β-delayed α emission [bβα=(1.59±0.06)×10-5]. Our value for bβα is 33% larger than previously held, leading to a substantial increase in γ11. Our revised value for γ11 is in good agreement with the value obtained in α-transfer studies and the weighted average of the two gives a robust and precise determination of γ11, which provides significantly improved constraints on the C12(α,γ) cross section in the energy range relevant to hydrostatic He burning.
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13.
  • Kirsebom, O. S., et al. (författare)
  • The 8B neutrino spectrum
  • 2010
  • Ingår i: 11th Symposium on Nuclei in the Cosmos, NIC 2010; Heidelberg; Germany; 19 July 2010 through 23 July 2010. - 1824-8039.
  • 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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14.
  • Marroquin, I., et al. (författare)
  • MULTI-PARTICLE EMISSION FROM Ar-31 AT ISOLDE
  • 2016
  • Ingår i: Acta Physica Polonica, Series B.. - 1509-5770 .- 0587-4254. ; 47:3, s. 747-754
  • Tidskriftsartikel (refereegranskat)abstract
    • A multi-particle decay experiment was successfully performed at the ISOLDE Decay Station. In this new permanent station, devoted to beta-decay studies, the novel MAGISOL Si-Plugin Chamber was installed to study the exotic decay modes of the proton drip-line nucleus Ar-31. The motivation was to search for beta 3p and beta 3p gamma channels, as well as to provide information on resonances in S-30 and P-29 relevant for the astrophysical rp-process. Description of the experimental set-up and preliminary results are presented.
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15.
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16.
  • Borge, M. J. G., et al. (författare)
  • Rare beta p decays in light nuclei
  • 2013
  • Ingår i: Journal of Physics G: Nuclear and Particle Physics. - : IOP Publishing. - 0954-3899 .- 1361-6471. ; 40:3, s. art.no. 035109-
  • 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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17.
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18.
  • Kirsebom, O. S., et al. (författare)
  • Observation of gamma-delayed 3 alpha breakup of the 15.11 and 12.71 MeV states in C-12
  • 2009
  • Ingår i: Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 680:1, s. 44-49
  • Tidskriftsartikel (refereegranskat)abstract
    • The reactions B-10(He-3, p alpha alpha alpha) at 4.9 MeV and B-11(He-3, d alpha alpha alpha) at 8.5 MeV have been used to investigate the gamma decay of states in C-12. By measuring the four-body final state in complete kinematics we are able to detect gamma transitions indirectly. We find gamma transitions from the 15.11 MeV state in C-12 to the 12.71, 11.83, 10.3 and 7.65 MeV states followed by their breakup into three alpha particles. The relative gamma-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 gamma decays going to the bound states. We obtain Gamma(alpha)/Gamma = (2.8 +/- 1.2)% for the isospinforbidden alpha decay of the 15.11 MeV state. From the 12.71 MeV state we find gamma transitions to the 10.3 and 7.65 MeV states. The relative gamma-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 gamma decays going to the bound states. Finally. we discuss the relation between the beta decay of N-12 and B-12 to states in C-12 and the gamma decay of the 15.11 MeV analog in C-12 to the same states. (C) 2009 Elsevier B.V. All rights reserved.
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19.
  • Alcorta, M., et al. (författare)
  • Nuclear Structure of C-12 from Break-up Studies in Complete Kinematics
  • 2009
  • Ingår i: AIP Conference Proceedings. - : AIP. - 1551-7616 .- 0094-243X. - 9780735407022 ; 1165, s. 27-30 461
  • 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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20.
  • Kirsebom, O. S., et al. (författare)
  • Improved Limit on Direct α Decay of the Hoyle State
  • 2012
  • Ingår i: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 108:20, s. 202501-
  • 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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21.
  • Tengblad, Olof, 1957, et al. (författare)
  • 12C formation: A classical quest in new light
  • 2011
  • Ingår i: AIP Conference Proceedings. - : AIP. - 1551-7616 .- 0094-243X. - 9780735409378 ; 1377, s. 270-274
  • 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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22.
  • Tengborn, Elisabeth, 1978, et al. (författare)
  • The 8Li + 2H reaction studied in inverse kinematics at 3.15 MeV/nucleon using the REX-ISOLDE post-accelerator
  • 2011
  • Ingår i: Physical Review C - Nuclear Physics. - 2469-9985 .- 2469-9993. ; 84:6, s. 064616-
  • Tidskriftsartikel (refereegranskat)abstract
    • The reaction 8Li + 2H has been studied in inverse kinematics at the incident energy of 3.15 MeV/nucleon, using the REX-ISOLDE post-accelerator. The reaction channels corresponding to (d,p), (d,d), and (d,t) reactions populating ground states and low-lying excited states in 7–9Li have been identified and the related angular distributions extracted and compared with coupled-channels, distorted-wave Born approximation (DWBA), and coupled-reaction-channels calculations. For the inelastic and (d,t) channels we find that higher order effects are very important and hence one needs to go beyond the simple DWBA to extract reliable structure information from these processes.
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