| 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. |
- Hadynska-Klek, K., et al.
(författare)
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Superdeformed and Triaxial States in Ca-42
- 2016
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Ingår i: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 117:6
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Tidskriftsartikel (refereegranskat)abstract
- Shape parameters of a weakly deformed ground-state band and highly deformed slightly triaxial sideband in Ca-42 were determined from E2 matrix elements measured in the first low-energy Coulomb excitation experiment performed with AGATA. The picture of two coexisting structures is well reproduced by new state-of-the-art large-scale shell model and beyond-mean-field calculations. Experimental evidence for superdeformation of the band built on 0(2)(+) has been obtained and the role of triaxiality in the A similar to 40 mass region is discussed. Furthermore, the potential of Coulomb excitation as a tool to study superdeformation has been demonstrated for the first time.
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| 3. |
- Browne, F., et al.
(författare)
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Pairing Forces Govern Population of Doubly Magic Ca-54 from Direct Reactions
- 2021
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Ingår i: Physical Review Letters. - : American Physical Society (APS). - 0031-9007 .- 1079-7114. ; 126:25
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Tidskriftsartikel (refereegranskat)abstract
- Direct proton-knockout reactions of Sc-55 at similar to 220 MeV/nucleon were studied at the RIKEN Radioactive Isotope Beam Factory. Populated states of Ca-54 were investigated through -ray and invariant-mass spectroscopy. Level energies were calculated from the nuclear shell model employing a phenomenological intemucleon interaction. Theoretical cross sections to states were calculated from distorted-wave impulse approximation estimates multiplied by the shell model spectroscopic factors, which describe the wave function overlap of the Sc-55 ground state with states in Ca-54. Despite the calculations showing a significant amplitude of excited neutron configurations in the ground-state of Sc-55, valence proton removals populated predominantly the ground state of Ca-54. This counterintuitive result is attributed to pairing effects leading to a dominance of the ground-state spectroscopic factor. Owing to the ubiquity of the pairing interaction, this argument should be generally applicable to direct knockout reactions from odd-even to even-even nuclei.
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| 4. |
- Birkenbach, B., et al.
(författare)
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Spectroscopy of the neutron-rich actinide nucleus U-240 following multinucleon-transfer reactions
- 2015
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Ingår i: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 92:4
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Tidskriftsartikel (refereegranskat)abstract
- Background: Nuclear structure information for the neutron-rich actinide nuclei is important since it is the benchmark for theoretical models that provide predictions for the heaviest nuclei. Purpose: gamma-ray spectroscopy of neutron-rich heavy nuclei in the actinide region. Method: Multinucleon-transfer reactions in Zn-70 + U-238 and Xe-136 + U-238 have been measured in two experiments performed at the INFN Legnaro, Italy. In the Zn-70 experiment the high-resolution HPGe Clover Array (CLARA) coupled to the magnetic spectrometer PRISMA was employed. In the Xe-136 experiment the high-resolution Advanced Gamma Tracking Array (AGATA) was used in combination with PRISMA and the Detector Array for Multinucleon Transfer Ejectiles (DANTE). Results: The ground-state band (g.s. band) of U-240 was measured up to the 20(+) level and a tentative assignment was made up to the (24(+)) level. Results from gamma gamma coincidence and from particle coincidence analyses are shown. Moments of inertia (MoI) show a clear upbend. Evidence for an extended first negative-parity band of U-240 is found. Conclusions: A detailed comparison with latest calculations shows best agreement with cranked relativistic Hartree-Bogoliubov (CRHB) calculations for the g.s. band properties. The negative-parity band shows the characteristics of a K-pi = 0 band based on an octupole vibration.
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| 5. |
- Sahin, E., et al.
(författare)
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Shell evolution beyond N=40 : Cu-69,Cu-71,Cu-73
- 2015
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Ingår i: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 91:3
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Tidskriftsartikel (refereegranskat)abstract
- The level structure of the neutron-rich Cu-69, Cu-71, and Cu-73 isotopes has been investigated by means of multinucleon transfer reactions. The experiment was performed at Laboratori Nazionali di Legnaro using the AGATA Demonstrator array coupled to the PRISMA magnetic spectrometer. Lifetimes of excited states in Cu nuclei were measured with the recoil-distance Doppler-shift method. The resulting electromagnetic matrix elements for transitions from excited states in Cu-69,Cu-71,Cu-73 nuclei are used to assess the collective or single-particle character of these states. The results are compared with predictions of large-scale shell-model calculations, giving further insight into the evolution of the proton pf shell as neutrons fill the 1g(9/2) orbital.
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| 6. |
- John, P. R., et al.
(författare)
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Shape evolution in the neutron-rich osmium isotopes : Prompt gamma-ray spectroscopy of Os-196
- 2014
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Ingår i: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 90:2, s. 021301-
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Tidskriftsartikel (refereegranskat)abstract
- The shape transition in the neutron-rich Os isotopes is studied by investigating the neutron-rich Os-196 nucleus through in-beam gamma-ray spectroscopy using a two-proton transfer reaction from a Pt-198 target to a Se-82 beam. The beam-like recoils were detected and identified with the large-acceptance magnetic spectrometer PRISMA, and the coincident gamma rays were measured with the advanced gamma tracking array (AGATA) demonstrator. The de-excitation of the low-lying levels of the yrast-band of Os-196 were identified for the first time. The results are compared with state-of-the-art beyond-mean-field calculations, performed for the even-even Os188-198 isotopes. The new results suggest a smooth transition in the Os isotopes from a more axial rotational behavior towards predominately vibrational nuclei through triaxial configurations. An almost perfect gamma-unstable/triaxial rotor yrast band is predicted for Os-196 which is in agreement with the experimentally measured excited states.
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| 7. |
- Pellegri, L., et al.
(författare)
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Pygmy dipole resonance in Sn-124 populated by inelastic scattering of O-17
- 2014
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Ingår i: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 738, s. 519-523
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Tidskriftsartikel (refereegranskat)abstract
- The gamma decay from the high-lying states of Sn-124 was measured using the inelastic scattering of O-17 at 340 MeV. The emitted gamma rays were detected with high resolution with the AGATA demonstrator array and the scattered ions were detected in two segmented Delta E-E silicon telescopes. The angular distribution was measured both for the gamma rays and the scattered O-17 ions. An accumulation of E1 strength below the particle threshold was found and compared with previous data obtained with (gamma,gamma') and (alpha,alpha'gamma) reactions. The present results of elastic scattering, and excitation of E2 and E1 states were analysed using the DWBA approach. From this comprehensive description the isoscalar component of the 1-excited states was extracted. The obtained values are based on the comparison of the data with DWBA calculations including a form factor deduced using a microscopic transition density.
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| 8. |
- John, P. R., et al.
(författare)
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In-beam gamma-ray spectroscopy of the neutron-rich platinum isotope Pt-200 toward the N=126 shell gap
- 2017
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Ingår i: Physical Review C. - : AMER PHYSICAL SOC. - 2469-9985 .- 2469-9993. ; 95:6
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Tidskriftsartikel (refereegranskat)abstract
- The neutron-rich nucleus Pt-200 is investigated via in-beam gamma-ray spectroscopy to study the shape evolution in the neutron-rich platinum isotopes towards the N = 126 shell closure. The two-neutron transfer reaction Pt-198(Se-82, Se-80)Pt-200 is used to populate excited states of Pt-200. The Advanced Gamma Ray Tracking Array (AGATA) demonstrator coupled with the PRISMA spectrometer detects gamma rays coincident with the Se-80 recoils, the binary partner of Pt-200. The binary partner method is applied to extract the gamma-ray transitions and build the level scheme of Pt-200. The level at 1884 keV reported by Yates et al. [S. W. Yates, E. M. Baum, E. A. Henry, L. G. Mann, N. Roy, A. Aprahamian, R. A. Meyer, and R. Estep, Phys. Rev. C 37, 1889 (1988)] was confirmed to be at 1882.1 keV and assigned as the (6(1)(+)) state. An additional gamma ray was found and it presumably deexcites the (8(1)(+)) state. The results are compared with state-of-the-art beyond mean-field calculations, performed for the even-even Pt190-204 isotopes, revealing that Pt-200 marks the transition from the gamma-unstable behavior of lighter Pt nuclei towards a more spherical one when approaching the N = 126 shell closure.
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| 9. |
- Aggarwal, MM, et al.
(författare)
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Centrality dependence of charged-neutral particle fluctuations in 158A (GeVPb)-Pb-208+Pb-208 collisions
- 2003
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Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 67:4
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Tidskriftsartikel (refereegranskat)abstract
- Results on the study of localized fluctuations in the multiplicity of charged particles and photons produced in 158A GeV/c Pb+Pb collisions are presented for varying centralities. The charged versus neutral particle multiplicity correlations in common phase space regions of varying azimuthal sizes are analyzed by two different methods. Various types of mixed events are constructed to probe fluctuations arising from different sources. The measured results are compared to those from simulations and from mixed events. The comparison indicates the presence of nonstatistical fluctuations in both the charged particle and photon multiplicities in limited azimuthal regions. However, no correlated charged-neutral fluctuations, a possible signature of formation of disoriented chiral condensates, are observed. An upper limit on the production of disoriented chiral condensates is set.
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| 10. |
- Aggarwal, MM, et al.
(författare)
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Transverse mass distributions of neutral pions from Pb-208-induced reactions at 158 center dot A GeV
- 2002
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Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 23:2, s. 225-236
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Tidskriftsartikel (refereegranskat)abstract
- Results on transverse mass spectra of neutral pious measured at central rapidity are presented for impact parameter selected 158-A GeV Pb + Pb-1 and Pb + Nb collisions. The distributions cover the range 0.5 GeV/c(2) less than or equal to MT - Mo less than or equal to 4 GeV/c(2). The change of the spectral shape and the multiplicity with centrality is studied in detail. In going from p+p to semi-peripheral Pb+Pb collisions there is a nuclear enhancement increasing with transverse mass similar to the well known Cronin effect, while for very central collisions this enhancement appears to be weaker than expected.
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