| 1. |
- Aleksandrov, D., et al.
(författare)
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Halo excitations in fragmentation of He-6 at 240 MeV/u on carbon and lead targets
- 2000
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Ingår i: Nuclear Physics A. - 0375-9474. ; 669:1-2, s. 51-64
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Tidskriftsartikel (refereegranskat)abstract
- Dissociation of a 240 MeV/u beam of He-6, incident on carbon and lead targets, has been studied in kinematically complete experiments to investigate low-lying excitation modes in the halo nucleus He-6. It is shown that alignment effects characterize the inelastic scattering and allow an unambiguous assignment of the spin of a narrow resonance observed in the excitation energy spectrum. The differential cross sections for the He-6 inelastic scattering on carbon and lead targets were deduced from the measured moments of the two neutrons and the a-particle. An analysis of these distributions shows that quadrupole and, possibly, monopole excitations characterize the hadronic interaction, while the dipole mode is dominating in Coulomb dissociation. Neither theoretically predicted new resonance states in He-6 nor nuclear excitation of a dipole mode were found. Direct evidence has been obtained for strong suppression of Coulornb post-acceleration in direct Coulomb breakup in a lead target.
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| 2. |
- Aleksandrov, D., et al.
(författare)
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Invariant mass spectrum and alpha-n correlation function studied in the fragmentation of He-6 on a carbon target
- 1998
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Ingår i: Nuclear Physics A. - 0375-9474. ; 633:2, s. 234-246
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Tidskriftsartikel (refereegranskat)abstract
- Momentum distributions and invariant mass spectra from the breakup of He-6 ions with an energy of 240 MeV/u interacting with a carbon target have been studied. The data were used to extract information about the reaction mechanism which is influenced by the structure of He-6. It is found that the dominant reaction mechanism is a two-step process: knock out of one neutron followed by the decay of the He-5 resonance. The shape of the (alpha+n) two-body invariant mass spectrum is interpreted as mainly reflecting the 5He ground state which is a J(pi) = 3/2(-) resonance. However, no evidence for correlations between cu particles and neutrons is observed in the momentum widths of the distributions. It is demonstrated that a combined analysis of the two-body invariant mass spectrum and an appropriate correlation function may be used to determine the properties of the intermediate resonance. (C) 1998 Elsevier Science B.V.
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| 3. |
- Axelsson, L., et al.
(författare)
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Beta decay of Ar-31
- 1998
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Ingår i: Nuclear Physics A. - 0375-9474. ; 634:4, s. 475-496
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Tidskriftsartikel (refereegranskat)abstract
- A complete study of Ar-31 beta decay has been made by high-resolution charged-particle and gamma-ray spectroscopy. Beta-delayed radiation was detected by an array of three charged-particle detectors and a large-volume germanium detector. Fifteen new energy levels were discovered in Cl-31. The beta-strength distribution, measured to 14.5 MeV, is compared with a shell-model calculation in the full sd space. The quenching of the Gamow-Teller strength and the isospin impurity of the IAS in Cl-31 are discussed. (C) 1998 Published by Elsevier Science B.V.
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| 4. |
- Axelsson, L., et al.
(författare)
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Deriving the angular variation of p(parallel to)-distributions for halo neutrons with robust statistics
- 2001
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Ingår i: Nuclear Physics A. - 0375-9474. ; 679:3-4, s. 215-230
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Tidskriftsartikel (refereegranskat)abstract
- The longitudinal neutron momentum distribution from core breakup of Li-11 and Be-11 have been measured at 29.9 MeV/u and 38.5 MeV/u, respectively. Separate measurements on Li-9 and Be-10 allowed extraction of the halo neutron distribution. The shapes of the distributions are analyzed using robust and descriptive statistics, For both isotopes the shape is changing with angle. (C) 2001 Elsevier Science B.V. All rights reserved.
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| 5. |
- Axelsson, L., et al.
(författare)
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Two-proton emission in the decay of Ar-31
- 1998
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Ingår i: Nuclear Physics A. - 0375-9474. ; 628:3, s. 345-362
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Tidskriftsartikel (refereegranskat)abstract
- Several beta-delayed two-proton branches were observed in the decay of Ar-31, the most intense ones proceeding through the isobaric analogue state (IAS) in Cl-31. The mechanism of the two-proton emission is studied via the energy and angular distributions of the two protons, Simultaneous emission of the two protons fits the present data well, sequential decays might also describe them. Independent of the decay mechanism, a spin of 5/2 for the IAS is suggested, An improved limit on the direct two-proton emission fi om the ground state of Ar-31 is presented, (C) 1998 Elsevier Science B.V.
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| 6. |
- Baumann, T., et al.
(författare)
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Longitudinal momentum distributions of C-16,C-18 fragments after one-neutron removal from C-17,C-19
- 1998
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Ingår i: Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics. - 0370-2693. ; 439:3-4, s. 256-261
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Tidskriftsartikel (refereegranskat)abstract
- The fragment separator FRS at GSI was used as an energy-loss spectrometer to measure the longitudinal momentum distributions of C-16,C-18 fragments after one-neutron removal reactions in C-17,C-19 impinging on a carbon target at about 910 MeV/u. The distributions in the projectile frames are characterized by a FWHM of 141 +/- 6 MeV/c for C-16 and 69 +/- 3 MeV/c for C-18. Th, results are compared with experimental data obtained at lower energies and discussed within existing theoretical models. (C) 1998 Elsevier Science B.V. AU rights reserved.
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| 7. |
- Borge, M. J. G., et al.
(författare)
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Elucidating halo structure by beta decay: beta gamma from the Li-11 decay
- 1997
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Ingår i: Physical Review C - Nuclear Physics. - 2469-9985 .- 2469-9993. ; 55:1, s. R8-R11
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Tidskriftsartikel (refereegranskat)abstract
- New values for the gamma ray intensities following the beta decay of Li-11 are presented. Special emphasis is put on the determination of the Gamow-Teller transition Li-11 --> Be-11 (1/2(-), 320 keV) to the only bound excited state in Be-11. We show that a shell-model calculation can simultaneously reproduce the half-life of Li-11 and the newly measured branching ratio to the 1/2(-) state provided the Li-11 ground state wave function contains about 50% of s-wave neutron components.
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| 8. |
- Borge, M. J. G., et al.
(författare)
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Probing the Li-11 halo structure through beta-decay into the Be-11(*) (18 MeV) state
- 1997
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Ingår i: Nuclear Physics A. - 0375-9474. ; 613:3, s. 199-208
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Tidskriftsartikel (refereegranskat)abstract
- An experimental study of beta-delayed charged particles (H, He, Be) from Li-11 shows a beta-feeding to an excited state at 18.15(15) MeV in Be-11 with a large Gamow-Teller strength, B-GT greater than or equal to 1.6. Branching ratios and reduced widths of 2-, 3- and 5- particle decay channels of this state are extracted, A strong suppression of the neutron branch from the 18 MeV state to the Be-10(g.s.) is observed, We suggest that the measured partial width may be sensitive to the (p(1/2))(2) component in the Li-11 halo, A rough estimate indicates that the (p(1/2))(2) component is not the dominant one in the halo wave-function.
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| 9. |
- Chulkov, L. V., et al.
(författare)
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Large spin alignment of the unbound He-5 fragment after fragmentation of 240 MeV/nucleon He-6
- 1997
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Ingår i: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 79:2, s. 201-204
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Tidskriftsartikel (refereegranskat)abstract
- Peripheral fragmentation of a 240 MeV/nucleon beam of the halo nucleus He-6 incident on carbon target has been studied in a kinematically complete experiment. It is found that one-neutron stripping to the unbound nucleus He-5 is the dominant fragmentation mechanism and that it leads to a spin alignment of He-5 in a plane perpendicular to the He-5 momentum vector. This is expected to be a common feature for all neutron halo nuclei.
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| 10. |
- Fynbo, H. O. U., et al.
(författare)
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Ar-31 examined: New limit on the beta-delayed three-proton branch
- 1999
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Ingår i: Physical Review C - Nuclear Physics. - 2469-9985 .- 2469-9993. ; 59:4, s. 2275-2277
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Tidskriftsartikel (refereegranskat)abstract
- We have remeasured the decay of Ar-31 with a setup sensitive to multiparticle decay branches and obtained. a new limit of 1.1 x 10(-3) (99% C.L.) on the beta-delayed three-proton branch between the isobaric analog state in Cl-31 and the ground state of Si-28. This a factor of 17 below the previously reported first observation of beta-delayed three-proton emission in Ar-31. The limit on a possible beta 3p branch to the first excited state in Si-28 is 2.9 x 10(-4). [S0556-2813(99)04404-0].
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| 11. |
- Fynbo, H. O. U., et al.
(författare)
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The beta 2p decay mechanism of Ar-31
- 2000
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Ingår i: Nuclear Physics A. - 0375-9474. ; 677, s. 38-60
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Tidskriftsartikel (refereegranskat)abstract
- We have measured the beta-decay of Ar-31 with a high granularity setup sensitive to multiparticle decay branches. Two-proton emission is observed from the isobaric analog state in Cl-31 to the four lowest states in P-29 and furthermore from a large number of states fed in Gamow-Teller transitions. The mechanism of two-proton emission is studied via energy and angular correlations between the two protons. In all cases the mechanism is found to be sequential yielding information about states in S-30 up to 8 MeV excitation energy. Improved data on the beta-delayed one-proton branches together with the two-proton data provide precise information about the beta-strength distribution up to 15 MeV excitation energy.
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| 12. |
- Grevy, S., et al.
(författare)
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Core-breakup reactions of the halo nuclei Be-11 and Li-11: momentum distributions and shadow effects
- 1999
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Ingår i: Nuclear Physics A. - 0375-9474. ; 650:1, s. 47-61
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Tidskriftsartikel (refereegranskat)abstract
- The halo nuclei Be-11 and Li-11 have been studied in core-breakup reactions where the halo neutrons are expected to be released without a major distortion due to the reaction. The widths of the halo-neutron momentum distributions have been extracted in coincidence with He fragments, Gamma = 32 +/- 4 MeV/c, and Li fragments, Gamma = 42 +/- 4 MeV/c for Be-11 and with He fragments, Gamma =42+/-6 MeV/c for Li-11. The Be-11 breakup gives a very low neutron multiplicity of 0.38+/-0.09 which is a manifestation of the shadowing of the neutron in the core-breakup reaction. This value can be understood from a simple theoretical calculation, which also accounts for the observed transverse momentum widths at small angles. (C) 1999 Elsevier Science B.V.
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| 13. |
- Honkanen, A., et al.
(författare)
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Fine structure in the beta-delayed proton decay of Ar-33
- 1996
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Ingår i: Nuclear Physics A. - 0375-9474. ; 611:1, s. 47-55
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Tidskriftsartikel (refereegranskat)abstract
- Low-energy beta-delayed protons from Ar-33 have been measured for the first time, The data reveal states, which, despite unfavourable barrier penetrability values, strongly decay to the first excited 2(+) state in S-32. The observation is discussed in terms of the standard shell model, A natural explanation is provided by the large spectroscopic amplitudes, involving s(1/2) and d(3/2) orbitals, as well as the l = 0 barrier penetrability, favouring the decay to the 2(+) state.
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| 14. |
- Marques, F. M., et al.
(författare)
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Neutrons from the breakup of C-19
- 1996
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Ingår i: Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics. - 0370-2693. ; 381:4, s. 407-412
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Tidskriftsartikel (refereegranskat)abstract
- Neutrons arising from the breakup of a 30 MeV/nucleon C-19 beam on a tantalum target have been measured using the 98 element array DEMON. A narrow, forward peaked neutron angular distribution, with a corresponding momentum spread considerably smaller than those measured simultaneously for N-21, O-22 and F-24 was observed for charged fragments with Z
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| 15. |
- Mukha, I., et al.
(författare)
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Observation of the Li-11(beta d) decay
- 1996
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Ingår i: Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 367:1-4, s. 65-69
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Tidskriftsartikel (refereegranskat)abstract
- Experimental data from the decay of Li-11 show for the first time the presence of beta-delayed deuterons with a branching ratio larger than 10(-4). To distinguish between beta d and beta t events the decays of the daughter nuclei Li-9 and Li-8 were identified in the energy and decay time spectra. Furthermore, a time correlation analysis between the beta d events and the subsequent daughter decays was performed.
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| 16. |
- Nilsson, Thomas, 1965, et al.
(författare)
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He-6 and neutron momentum distributions from He-8 in nuclear break-up reactions at 240 MeV/u
- 1996
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Ingår i: Nuclear Physics A. - 0375-9474. ; 598:3, s. 418-434
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Tidskriftsartikel (refereegranskat)abstract
- Neutron and He-6 momentum distributions from He-8 break-up reactions in a C target have been measured at 240 MeV/u. The two-neutron removal cross section was found to be sigma(-2n) = 0.27 +/- 0.03 b. The nature of the momentum distributions is interpreted in some simple reaction scenarios.
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| 17. |
- Smedberg, Martin, 1967
(författare)
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Probing the Drip-Lines through Momentum Distributions
- 1998
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- About a decade ago it was found that nuclei in the vicinity of the neutron drip-line under certain circumstances develop very extended valence neutron distributions, a phenomenon today known as halo states. The recent development of radioactive nuclear beams has provided us with a perfect tool for investigating these particular nuclei. There are several nuclei that exhibit halo structure such as 11Be, 19C (one-neutron halos), 6He, 11Li, 14Be, 17B (two-neutron halos), and 8He (four-neutron halo). Among their signatures, large total reaction and halo-removal cross-sections and narrow momentum distributions have been found. This thesis work will mainly deal with fragment momentum distributions detected in nuclear break-up of halos. We want to find answers to some fundamental questions like: What will actually happen when a loosely bound projectile collides with a target nucleus, and to what extent does the measured momentum of a break-up fragment reflect its internal motion inside the projectile? The simple interpretation of the momentum distribution in form of a Fourier transform of the wave function has recently been questionable. The peripheral nature of the halo removal process and the final-state interaction in the exit channels are shown to play an important role in defining the final momentum distribution. We have calculated particle momentum distributions from 8He fragmentation on a light target, utilizing an analytical five-body wave function for 8He. Without additional fitting parameters the experimental neutron and 6He transverse momentum distributions were reproduced, and the main ingredients in the fragmentation process were found to be the neutron motion in 8He, the neutron-target interaction, and the final-state interaction between the neutron and 6He through the 7He resonance. Core longitudinal momentum distributions for one-nucleon halos have been investigated. The momentum distribution is shown to be determined mainly by the one-nucleon separation energy and the orbital angular momentum of the halo nucleon, and due to the reaction mechanism sensitive to the asymptotic part of the wave function only. Detailed calculations for the loosely bound carbon isotopes 17,19C and the one-proton halo 8B have been performed and compared to existing experimental data.
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