| 1. |
- Reifarth, R., et al.
(författare)
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Nuclear astrophysics with radioactive ions at FAIR
- 2016
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Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 665:1
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Konferensbidrag (refereegranskat)abstract
- The nucleosynthesis of elements beyond iron is dominated by neutron captures in the s and r processes. However, 32 stable, proton-rich isotopes cannot be formed during those processes, because they are shielded from the s-process flow and r-process beta-decay chains. These nuclei are attributed to the p and rp process. For all those processes, current research in nuclear astrophysics addresses the need for more precise reaction data involving radioactive isotopes. Depending on the particular reaction, direct or inverse kinematics, forward or time-reversed direction are investigated to determine or at least to constrain the desired reaction cross sections. The Facility for Antiproton and Ion Research (FAIR) will offer unique, unprecedented opportunities to investigate many of the important reactions. The high yield of radioactive isotopes, even far away from the valley of stability, allows the investigation of isotopes involved in processes as exotic as the r or rp processes.
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| 2. |
- Jentschel, M., et al.
(författare)
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EXILL - a high-efficiency, high-resolution setup for gamma-spectroscopy at an intense cold neutron beam facility
- 2017
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Ingår i: Journal of Instrumentation. - : IOP PUBLISHING LTD. - 1748-0221. ; 12
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Tidskriftsartikel (refereegranskat)abstract
- In the EXILL campaign a highly efficient array of high purity germanium (HPGe) detectors was operated at the cold neutron beam facility PF1B of the Institut Laue-Langevin (ILL) to carry out nuclear structure studies, via measurements of gamma-rays following neutron-induced capture and fission reactions. The setup consisted of a collimation system producing a pencil beam with a thermal capture equivalent flux of about 10(8) ns(-1)cm(2) at the target position and negligible neutron halo. The targetwas surrounded by an array of eight to ten anti-Compton shielded EXOGAMClover detectors, four to six anti-Compton shielded large coaxial GASP detectors and two standard Clover detectors. For a part of the campaign the array was combined with 16 LaBr3:(Ce) detectors from the FATIMA collaboration. The detectorswere arranged in an array of rhombicuboctahedron geometry, providing the possibility to carry out very precise angular correlation and directional-polarization correlation measurements. The triggerless acquisition system allowed a signal collection rate of up to 6 x 10(5) Hz. The data allowed to set multi-fold coincidences to obtain decay schemes and in combination with the FATIMA array of LaBr3:(Ce) detectors to analyze half-lives of excited levels in the pico-to microsecond range. Precise energy and efficiency calibrations of EXILL were performed using standard calibration sources of Ba-133, Co-60 and Eu-152 as well as data from the reactions Al-27(n, gamma)Al-28 and Cl-35(n,gamma)Cl-36 in the energy range from 30 keV up to 10MeV.
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| 3. |
- Kögler, T., et al.
(författare)
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Fast-neutron-induced fission cross section of Pu 242 measured at the neutron time-of-flight facility nELBE
- 2019
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Ingår i: Physical Review C. - 2469-9985. ; 99:2
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Tidskriftsartikel (refereegranskat)abstract
- The fast-neutron-induced fission cross section of Pu242 was measured at the neutron time-of-flight facility nELBE. A parallel-plate fission ionization chamber with novel, homogeneous, large-area Pu242 deposits on Si-wafer backings was used to determine this quantity relative to the IAEA neutron cross-section standard U235(n,f) in the energy range of 0.5 to 10 MeV. The number of target nuclei was determined from the measured spontaneous fission rate of Pu242. This helps to reduce the influence of the fission fragment detection efficiency on the cross section. Neutron transport simulations performed with geant4, mcnp6, and fluka2011 are used to correct the cross-section data for neutron scattering. In the reported energy range the systematic uncertainty is below 2.7% and on average the statistical uncertainty is 4.9%. The determined results show an agreement within 0.67(16)% to recently published data and a good accordance to current evaluated data sets.
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| 4. |
- Neyens, G., et al.
(författare)
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g-Factor Measurements on Relativistic Isomeric Beams Produced by Fragmentation and U-fission: The g-RISING Project at GSI
- 2007
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Ingår i: Acta Physica Polonica. Series B: Elementary Particle Physics, Nuclear Physics, Statistical Physics, Theory of Relativity, Field Theory. - 0587-4254. ; 38:4, s. 1237-1247
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Tidskriftsartikel (refereegranskat)abstract
- Within the RISING (Rare ISotope INvestigations @ GSI) Collaboration at GSI, g factor measurements have been performed on isomeric states in neutron-rich isotopes approaching Sn-132 and in the neutron deficient Pb-region (the g-RISING campaign). We present the experimental technique and some typical aspects related to such studies on relativistic beams selected with the FRS fragment separator. First results are presented for the (19/2(+)) 4.5 mu s isomeric state in Sn-127, which has been produced by means of fission of a relativistic U-238 beam on the one hand, and by the fragmentation of a relativistic Xe-136 beam on the other hand. Spin-alignment has been observed in both reactions. It was the first time that spin-alignment has been established in a relativistic fission reaction.
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| 5. |
- Atanasova, L., et al.
(författare)
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g-factor Measurements at RISING: The Cases of 127Sn and 128Sn
- 2010
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Ingår i: Europhysics Letters. - : IOP Publishing. - 0295-5075. ; 91:4
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Tidskriftsartikel (refereegranskat)abstract
- We report on g-factor measurements of the 19/2(+) T-1/2 = 4.5(3) mu s isomer in Sn-127 and the 10(+) T-1/2 = 2.69(23) mu s isomer in Sn-128. These isomers were produced and spin-aligned in relativistic heavy-ion fragmentation at GSI and were selected and separated by the GSI fragment separator ( FRS). The gamma-rays of the isomeric decay were detected by the RISING gamma-ray spectrometer. The method of time-differential perturbed angular distributions was utilized. The measured g-factors, g(19/2(+); Sn-127) =-0.17(2) and g(10(+); Sn-128)=-0.20(4), are compared with shell model calculations. The measured g-factors confirm the predominantly nu h(11/2)(-2) and nu(s(1/2)(-1) h(11/2)(-2)) character of the 10(+) and 19/2(-) isomers in Sn-128 and Sn-127, respectively. The results demonstrate the feasibility of the method for similar measurements in exotic neutron-rich nuclei. Copyright (C) EPLA, 2010
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| 6. |
- Gadea, A, et al.
(författare)
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Hindered E4 decay of the 12(+) yrast trap in Fe-52
- 2005
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Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 619:1-2, s. 88-94
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Tidskriftsartikel (refereegranskat)abstract
- The gamma decay of the 12(+) yrast trap in Fe-52 has been measured for the first time. The two E4 gamma-branches to the 8(+) states are hindered with respect to other B(E4) reduced transition probabilities measured in the f(7/2) shell. The interpretation of the data is given in the full pf shell model framework, comparing the results obtained with different residual interactions. It is shown that measurements of hexadecapole transition probabilities constitute a powerful tool in discriminating the correct configuration of the involved wavefunctions.
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| 7. |
- Lozeva, R. L., et al.
(författare)
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New sub-us Isomers in 125Sn, 127Sn, 129Sn and Isomer Systematics of 124-130Sn
- 2008
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Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 77:6
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Tidskriftsartikel (refereegranskat)abstract
- New sub-mu s isomers have been observed in the neutron-rich Sn isotopes. Sn-125,Sn-127,Sn-129 nuclei have been produced in a relativistic fission reaction of U-238 on a Be-9 target at 750 A.MeV and by the fragmentation of Xe-136 at 600 A.MeV populating high-spin yrast states. In addition to the already known mu s isomers, three new ones with sub-mu s half-lives have been observed. These yrast isomers are the high-spin members of the nu(d(3/2)(-1)h(11/2)(-2)) and nu h(11/2)(-n), seniority v = 3 multiplets leading to isomeric (23/2(+)) and (27/2(-)) states, respectively. Added to the already known 19/2(+)mu s isomers in this region the current work completes the systematic information of neutron-hole excitations toward the filling of the last h(11/2) orbital at N = 82. The results are discussed in the framework of state-of-the-art shell-model calculations using realistic interactions.
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| 8. |
- Plettner, C., et al.
(författare)
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Very high rotational frequencies and band termination in 73Br
- 2000
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Ingår i: Physical Review C - Nuclear Physics. - 0556-2813. ; 62:1, s. 143131-143136
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Tidskriftsartikel (refereegranskat)abstract
- Rotational bands in 73Br have been investigated up to spins of I = 65/2 using the EUROBALL III spectrometer. One of the negative-parity bands displays the highest rotational frequency ℏω= 1.85 MeV reported to date in nuclei with A ≥ 25. At high frequencies, the experimental J(2) dynamic moment of inertia for all bands decreases to very low values, J(2) ≤ 10ℏ2 MeV-1. The bands are described in the configuration-dependent cranked Nilsson-Strutinsky model. The calculations indicate that one of the negative-parity bands is observed up to its terminating single-particle state at spin 63/2. This result establishes the first band termination in the A ≈ 70 mass region.
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| 9. |
- Borcan, C, et al.
(författare)
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First identification of excited states in the N = Z nucleus Br-70
- 1999
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Ingår i: EUROPEAN PHYSICAL JOURNAL A. - : SPRINGER VERLAG. ; 5:3, s. 243-246
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Excited states in the T-z = 0 nucleus Br-70 have been investigated using the reaction Ni-58(O-16,1p3n). gamma rays were detected with one EUROBALL CLUSTER detector and three single HPGe detectors. Charged particles and neutrons were registered with the Ro
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| 10. |
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| 11. |
- Jungclaus, A., et al.
(författare)
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Evidence for reduced collectivity around the neutron mid-shell in the stable even-mass Sn isotopes from new lifetime measurements
- 2011
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Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 695:1-4, s. 110-114
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Tidskriftsartikel (refereegranskat)abstract
- Precise measurements of the lifetimes of the first excited 2(+) states in the stable even-A Sn isotopes Sn112-124 have been performed using the Doppler shift attenuation technique. For the isotopes Sn-112, Sn-114 and Sn-116 the E2 transition strengths deduced from the measured lifetimes are in disagreement with the previously reported values and indicate a shallow minimum at N = 66. The observed deviation from a maximum at mid-shell is attributed to the obstructive effect of the S-1/2 neutron orbital in generating collectivity when near the Fermi level. (C) 2010 Elsevier B.V. All rights reserved.
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| 12. |
- Jungclaus, A., et al.
(författare)
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New lifetime measurements in the stable semimagic Sn isotopes using the Doppler-shift attenuation technique
- 2011
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Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 312:SECTION 9
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Tidskriftsartikel (refereegranskat)abstract
- Precise measurements of lifetimes in the picosecond range of excited states in the stable even-A Sn isotopes 112,114,116,122Sn have been performed using the Doppler shift attenuation technique. For the first excited 2+ states in 112Sn, 114Sn and 116Sn the E2 transition strengths deduced from the measured lifetimes are in disagreement with the previously adopted values. They indicate a shallow minimum at N = 66 in contrast to the maximum at mid-shell predicted by modern shell model calculations.
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| 13. |
- Lalovic, Natasa, et al.
(författare)
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Analysis of the Response of AGATA Detectors at GSI
- 2015
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Ingår i: EPJ Web of Conferences. - : EDP Sciences. - 2101-6275 .- 2100-014X. - 9782759817948 ; 93, s. 07007-07007
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Konferensbidrag (refereegranskat)abstract
- In 2012 and 2014 the γ-ray tracking spectrometer AGATA was operated at the SIS/FRS facility at GSI in Darmstadt, Germany. The performance of the array is discussed, outlining some important aspects of the offline data processing and analysis. Relying on the data obtained from measurements with standard γ-ray sources, a first estimate of the photopeak efficiency and peak-to-total (P/T) is presented.
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| 14. |
- Pausch, G., et al.
(författare)
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RoSiB - a 4 pi silicon ball for charged-particle detection in EUROBALL
- 2000
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - 0168-9002 .- 1872-9576. ; 443:03-feb, s. 304-318
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Tidskriftsartikel (refereegranskat)abstract
- A 4 pi silicon bail for detection and identification of light charged particles in large multidetector gamma-arrays as EUROBALL is presented. The design is based on a N = 42 ball with 12 pentagons and 30 hexagons as used in the GASP array. The absorptive material for gamma-rays is minimized to the detector thickness of 300 or 500 mu m and a 0.63 mm ceramic backing. The geometrical coverage is designed for about 90% of 4 pi. A pulse shape discrimination method with totally depleted detectors working in the reverse mount allows identifying protons and alpha-particles above an energy threshold of about 2 MeV. The performances of the ball were rested at the tandem - booster accelerator combination of the MPI Heidelberg in two experiments using the high-recoil reaction of 228 MeV Ni-58 + Ti-46 and the low-recoil reaction of 95 MeV O-16 + Ni-58. The two-dimensional spectra of zero-crossing (ZC) versus energy confirmed an excellent discrimination of protons and alpha-particles in all the detectors at different angles. The energy spectra of protons and alpha-particles measured in the experiments are presented. too. The gamma-spectra measured in coincidence with various combinations of emitted particles showed a high selectivity of the ball. The reduced total efficiency for protons of 59% and 55% and alpha-particles of 44% and 32% measured in a nuclear spectroscopy application is analyzed in a Monte-Carlo simulation (GEANT). It is due to a combined influence of a thick target needed to stop the recoiling residual nuclei and thick absorbers needed to protect the Si-detectors from scattered beam. The results along with the GEANT extrapolation to optimum experimental conditions confirm that RoSiB is a highly efficient and selective device for identification of rare reaction channels with heavy ions.
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| 15. |
- Pausch, G, et al.
(författare)
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RoSiB - a 4 pi silicon ball for charged-particle detection in EUROBALL
- 2000
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Ingår i: NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT. - : ELSEVIER SCIENCE BV, AMSTERDAM. - 0168-9002. ; 443:2-3, s. 304-318
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Tidskriftsartikel (refereegranskat)abstract
- A 4 pi silicon bail for detection and identification of light charged particles in large multidetector gamma-arrays as EUROBALL is presented. The design is based on a N = 42 ball with 12 pentagons and 30 hexagons as used in the GASP array. The absorptive
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| 16. |
- Rainovski, G, et al.
(författare)
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Shape coexistence at high spin in the N = Z+2 nucleus Se-70
- 2002
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Ingår i: Journal of Physics G: Nuclear and Particle Physics. - : IOP Publishing. - 0954-3899. ; 28:10, s. 2617-2625
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Tidskriftsartikel (refereegranskat)abstract
- The nucleus Se-70 was studied using the Ca-40(Ca-40, 2alpha2p) reaction at a beam energy of 185 MeV. Gamma rays were measured with the EUROBALL III spectrometer. The known positive-parity bands have been extended and one new band of positive parity and two of negative parity have been identified. These bands are interpreted in terms of the cranked Nilsson-Strutinsky approach. Calculations suggest that the two negative-parity bands, which have the same signature, are both based on a configuration with two protons and three neutrons lifted from the fp shell to the g(9/2) orbital, but at different nuclear shapes. This represents a shape coexistence at high spin.
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| 17. |
- Valiente-Dobon, JJ, et al.
(författare)
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Evidence for nontermination of rotational bands in Kr-74
- 2005
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Ingår i: Physical Review Letters. - 1079-7114. ; 95:23
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Tidskriftsartikel (refereegranskat)abstract
- Three rotational bands in Kr-74 were studied up to (in one case one transition short of) the maximum spin I-max of their respective single-particle configurations. Their lifetimes have been determined using the Doppler-shift attenuation method. The deduced transition quadrupole moments reveal a modest decrease, but far from a complete loss of collectivity at the maximum spin I-max. This feature, together with the results of mean field calculations, indicates that the observed bands do not terminate at I=I-max.
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| 18. |
- Walker, J., et al.
(författare)
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Magnetic moments of the first excited 2(+) states in the semi-magic Sn-112,Sn-114,Sn-116,Sn-122,Sn-124 isotopes
- 2011
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Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 84:1
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Tidskriftsartikel (refereegranskat)abstract
- The g factors of the first excited 2(+) states in the Sn-112,Sn-114,Sn-116,Sn-122,Sn-124 isotopes have been measured with high accuracy using the transient field technique in combination with Coulomb excitation in inverse kinematics. The experimental results are discussed in a qualitative way on the basis of empirical single-particle g factors of the relevant proton and neutron orbitals and are compared to a number of different theoretical calculations. The results are found to be best described by shell-model calculations in an extended configuration space. Clear evidence for the contribution of neutron pair excitations from the 1d(3/2) to the 0h(11/2) orbital to the wave function of the 2(1)(+) state in Sn-122,Sn-124 has been obtained.
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| 19. |
- DORING, J, et al.
(författare)
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HIGH-LYING 3-QUASI-PARTICLE BANDS AND SIGNATURE SPLITTING IN RB-81
- 1994
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Ingår i: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 50:4, s. 1845-1850
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Tidskriftsartikel (refereegranskat)abstract
- Two new high-lying level sequences of negative parity have been identified in the odd-proton nucleus Rb-81 by in-beam gamma-ray spectroscopy using the reactions Br-79(alpha, 2n) at 27 MeV and Zn-68(F-19, alpha2n) at 72 MeV. One sequence, dominated by M1 transitions, is interpreted as a three-quasiparticle band predominantly containing a neutron in the p1/2, p3/2, or f5/2 subshell coupled to g9/2 proton and g9/2 neutron excitations. The other new level sequence forms the three-quasiparticle extension of the unfavored negative-parity band, but the states decay also by E1 transitions. The signature splitting points to a configuration where an aligned g9/2 proton pair is involved.
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| 20. |
- Stefanescu, I, et al.
(författare)
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High-spin states and band terminations in As-69
- 2004
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Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 70:4
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Tidskriftsartikel (refereegranskat)abstract
- Excited levels in As-69 were studied using the Ca-40(S-32,3p)As-69 reaction at 95 and 105 MeV beam energy. Gamma rays were detected with the EUROBALL spectrometer operated in conjunction with the Neutron Wall and the charged-particle detector array EUCLIDES. New level sequences with positive and negative parity were identified from 3p-gammagamma and gammagammagamma coincidences. Spins were assigned to many of the levels on the basis of directional correlations of oriented states measurements. The previously observed positive-parity band was extended to spin 45/2(+) and it was found to exhibit a crossing with another configuration identified up to spin 53/2(+). Three negative-parity bands were observed for the first time up to spins (43/2(-)), 39/2(-), and (41/2(-)). The previously known band was extended to spin (49/2(-)). No evidence for superdeformation was found, despite very high counting statistics. Configurations were assigned to each of the observed bands through comparisons to the cranked Nilsson-Strutinsky calculations.
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| 21. |
- Stefanova, E. A., et al.
(författare)
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Four-quasiparticle alignments in Ge-66
- 2003
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Ingår i: Acta Physica Polonica B. - 0587-4254 .- 1509-5770. ; 34:4, s. 2237-2240
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Tidskriftsartikel (refereegranskat)abstract
- Above angular momentum 10(+), we found two positive-parity sequences, connected by energetically staggered DeltaI = 1 M1 transitions. The total Routhian surface calculations predict a strong triaxial deformation for them. To our knowledge, this is the first observation of staggered M1 transitions in a deformed four-quasiparticle pi(g(9/2)(2))v(g(9/2)(2)) regime.
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| 22. |
- Stefanova, E. A., et al.
(författare)
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Four-quasiparticle alignments in Ge-66
- 2003
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Ingår i: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 67:5
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Tidskriftsartikel (refereegranskat)abstract
- The neutron-deficient nucleus Ge-66 was populated at high spin in two experiments using the reaction Ca-40(S-32,alpha2p) at beam energies of 105 and 95 MeV. In the first experiment, a self-supporting Ca-40 target was used, while a gold-backed target of similar thickness was used in the second experiment. gamma rays were detected with the EUROBALL array, combined with the charged-particle detector array EUCLIDES and the Neutron Wall. The level scheme of Ge-66 was extended up to Eapproximate to18 MeV and I-pi=(23(-)). Above angular momentum 10(+), we found two sequences, connected by energetically staggered DeltaI=1 M1 transitions. The total Routhian surface calculations describe Ge-66 at lower spins as a gamma-soft nucleus having a moderate deformation of beta(2)approximate to0.23, while a triaxial deformation is predicted for the band structures above I-pi=10(+). To our knowledge, this is the first observation of staggered M1 transitions in a deformed four-quasiparticle pi(g(9/2)(2))nu(g(9/2)(2)) structure.
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| 23. |
- Stefanova, E. A., et al.
(författare)
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Observation of negative-parity high-spin states of As-68
- 2005
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Ingår i: European Physical Journal A. - : Springer Science and Business Media LLC. - 1434-6001 .- 1434-601X. ; 24:1, s. 1-4
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Tidskriftsartikel (refereegranskat)abstract
- The neutron-deficient nucleus As-68 was populated at high spin in two experiments using the reaction Ca-40(S-32, 3pn) at beam energies of 105 and 95 MeV. A self-supporting and a gold-backed, highly enriched Ca-40 target were used. Gamma rays were detected with the EUROBALL array, combined with the charged-particle detector array EUCLIDES and the Neutron Wall. The As-68 level scheme was considerably extended, especially at negative parity and many previous spin-parity assignments were confirmed or rejected. The total-Routhian-surface (TRS) calculations find shape coexistence and γ softness for the negative- and positive-parity states, respectively.
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| 24. |
- Wagner, L., et al.
(författare)
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Astrophysical S factor of the N 14 (p,γ) O 15 reaction at 0.4-1.3 MeV
- 2018
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Ingår i: Physical Review C. - : American Physical Society. - 2469-9985 .- 2469-9993. ; 97:1
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Tidskriftsartikel (refereegranskat)abstract
- The N14(p,γ)O15 reaction is the slowest reaction of the carbon-nitrogen cycle of hydrogen burning and thus determines its rate. The precise knowledge of its rate is required to correctly model hydrogen burning in asymptotic giant branch stars. In addition, it is a necessary ingredient for a possible solution of the solar abundance problem by using the solar N13 and O15 neutrino fluxes as probes of the carbon and nitrogen abundances in the solar core. After the downward revision of its cross section due to a much lower contribution by one particular transition, capture to the ground state in O15, the evaluated total uncertainty is still 8%, in part due to an unsatisfactory knowledge of the excitation function over a wide energy range. The present work reports precise S factor data at twelve energies between 0.357 and 1.292 MeV for the strongest transition, capture to the 6.79-MeV excited state in O15, and at ten energies between 0.479 and 1.202 MeV for the second strongest transition, capture to the ground state in O15. An R-matrix fit is performed to estimate the impact of the new data on astrophysical energies. The recently suggested slight enhancement of the 6.79-MeV transition at low energy could not be confirmed. The present extrapolated zero-energy S factors are S6.79(0)=1.24±0.11 keV b and SGS(0)=0.19±0.05 keV b.
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