Study of the γ decay of high-lying states in<sup>208</sup>Pb via inelastic scattering of<sup>17</sup>O ions

Bracco, A.; Crespi, F. C. L.

doi:10.1051/epjconf/20123803001

Cited by 7 publications

(7 citation statements)

References 49 publications

(34 reference statements)

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“…A first qualitative comparison to calculations within the relativistic quasiparticle time-blocking approximation (RQTBA) as well as quasiparticle phonon model (QPM) has shown good agreement to the experimental observation [19]: While the low-lying part of the E1 strength shows the described pattern of transition densities, which lead to an enhancement in the isoscalar E1 response, the higher lying states are of transition character towards the GDR and, thus, are suppressed in the isoscalar channel. Meanwhile, similar IS/IV energy behaviour of the low-lying E1 strength has been reported experimentally in inelastic scattering of 17 O off 208 Pb at low bombarding energies [23] as well as in other microscopic model calculations for different nuclei, see e.g. [9,24].…”

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confidence: 84%

Dipole excitations via isoscalar probes: The splitting of the pygmy dipole resonance in124Sn

et al. 2014

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Inelastic α-scattering excitation cross sections are calculated for electric dipole excitations in 124 Sn based on the transition densities obtained from the relativistic quasiparticle time-blocking approximation (RQTBA) in the framework of a semiclassical model. The calculation provides the missing link to directly compare the results from the microscopic RQTBA calculations to recent experimental data measured via the (α, α ′ γ) reaction, which show a structural splitting of the lowlying E1 strength often denoted as pygmy dipole resonance (PDR). The experimentally observed splitting is reproduced by the cross section calculations, which allows to draw conclusion on the structure of the PDR.The study of nuclei with neutron excess have been pursued in the last years with focus to the properties of collective states. Special attention has been devoted to the electric dipole strength at low excitation energy, the so called Pygmy Dipole Resonance (PDR), both in theory [1] as well as experimentally [2]. While the PDR represents an interesting new nuclear phenomenon itself, the connection of the (low-lying) E1 strength to the neutron skin of atomic nuclei [3][4][5][6][7][8][9][10][11] and to isovector parameters in the equation of state of nuclear matter [8,[12][13][14] as well as its possible importance for reaction rates in astrophysical scenarios [15,16] has further increased the interest in the PDR region. Different microscopic models predict the presence of the low-lying PDR states below the well-know (isovector) electric giant dipole resonance (IVGDR), see [1,2] and references therein. Most calculations show similar results for the transition densities of the low-lying E1 strength, which often is used to "define" the PDR states: The neutron and proton transition densities are in phase inside the nucleus and at the surface only the neutron part considerably contributes. The investigation of the PDR by means of isovector (IV) as well as isoscalar (IS) probes provides information on this structure of the involved transition densities, which show a strong mixing of isospin character. While for isovector probes (i.e. photons) data exist for various nuclei obtained mainly in nuclear resonance fluorescence (NRF) and Coulomb excitation (for a recent overview see [2]), only recently data on the PDR using an isoscalar probe became available [17][18][19][20][21]. Applying the (α, α ′ γ) coincidence method in combination with high-resolution γ-ray spectroscopy [22] allowed to * Electronic address: lanza@ct.infn.it study the PDR for several semi magic stable nuclei in αscattering experiments. The comparison to results from NRF revealed a surprising splitting of the PDR strength below the particle threshold into two groups [17,19]: the lower lying group of states is excited by both isoscalar and isovector probes while the states at higher energy are excited by photons only. A first qualitative comparison to calculations within the relativistic quasiparticle time-blocking approximation (RQTBA) as well as quasiparticle phonon mo...

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confidence: 84%

Dipole excitations via isoscalar probes: The splitting of the pygmy dipole resonance in124Sn

et al. 2014

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“…In recent years, several experimental and theoretical investigations, on both stable and radioactive nuclei, were made to learn on the microscopic properties of the pygmy states. An interesting feature of the pygmy states has been observed [5][6][7][8] in a number of different stable nuclei, by comparing results of photon-scattering and α scattering experiments. In particular, it has been found that one group of states is excited in both types of reactions, while another group of states at higher energies is only excited in the (γ, γ ) case [9].…”

Section: Sn Reactionmentioning

confidence: 99%

Nuclear Structure aspects of gamma decay from giant resonances

Bracco

Ceruti

Pellegri

2014

EPJ Web of Conferences

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Abstract. The gamma decay of the giant dipole resonance (including its tail region) is an important tool to probe the properties of these states, and thus to test the predictions of mean field theories. This paper focuses on two main aspects concerning the electric dipole excitation in nuclei. These are the study of the isospin character of the low energy tail of the Giant Dipole Resonance (GDR), the so-called Pygmy resonance, and the isospin mixing of nuclear systems at finite temperature. In the first case, the Pygmy resonance has been populated in the inelastic scattering reaction 17 O+ 124 Sn at 20 MeV/u. Its gamma decay has been measured using the AGATA Demonstrator and an array of 8 large volume LaBr 3 :Ce scintillators. In the second case, the gamma decay of the GDR in thermalized nuclear systems, formed in fusion evaporation reactions, has been used to investigate the isospin mixing in 80 Zr. For this work the reactions 40 Ca+ 40 Ca at 3.4 MeV/u and 37 Cl + 44 Ca at 2.6 MeV/u were used.

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“…A measurement of the high-lying states in 208 Pb has been made using 17 O beams at 20 MeV/u [30]. The γ decay following inelastic excitation was measured with the detector system AGATA Demonstrator, coupled to an array of large volume LaBr 3 :Ce scintillators and to an array of Si telescope detectors.…”

Section: Pygmy Resonance In 208 Pb By Inelastic Scattering Of 17 O Ionsmentioning

confidence: 99%

Nuclear Structure Studies with the AGATA Array at Legnaro

Leoni¹

2014

Acta Phys. Pol. B

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Results of three selected AGATA Demonstrator experiments performed at Legnaro National Laboratory of INFN (Italy), aiming at studying collective modes of excitations, such as rotation and vibration, under extreme conditions, are reported. Firstly, the K-hindrance to the γ decay is investigated in the warm rotating 174 W nucleus, focusing on the weakening of the selection rules of the K quantum number with excitation energy. A strong hindrance to the E1-decay between low-K and high-K rotational bands is found, giving evidence that K-mixing due to temperature effects is the leading phenomenon, contributing, for all discrete excited bands, to the progressive erosion of the K-quantum number with excitation energy. The second experiment concerns the study of the pygmy dipole resonance in the neutron rich 208 Pb nucleus, by inelastic scattering of 17 O at 20 MeV/u. The γ decay is measured with the AGATA Demonstrator coupled to an array of large volume LaBr 3 :Ce scintillators. A preliminary comparison with (γ,γ') data indicate that states in the 5-8 MeV energy interval belong to two different groups, one with an isoscalar character and the other with an isovector nature. Finally, the breaking of isospin symmetry is studied in the hot compound N = Z nucleus 80 Zr, by comparing the γ decay of the Giant Dipole Resonance from the fusion reactions 40 Ca+ 40 Ca at E beam = 136 MeV and 37 Cl+ 44 Ca at E beam = 95 MeV. Preliminary results show that the yield associated with the Giant Dipole Resonance is different in the two reactions because in self-conjugate nuclei the E1 selection rules forbid the decay between states with isospin I = 0. The experiment aims at providing information on the degree of isospin mixing at temperature around ≈ 2 MeV and to extrapolate the zero-temperature value, which is then compared with the latest predictions.

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Study of the γ decay of high-lying states in²⁰⁸Pb via inelastic scattering of¹⁷O ions

Cited by 7 publications

References 49 publications

Dipole excitations via isoscalar probes: The splitting of the pygmy dipole resonance in124Sn

Dipole excitations via isoscalar probes: The splitting of the pygmy dipole resonance in124Sn

Nuclear Structure aspects of gamma decay from giant resonances

Nuclear Structure Studies with the AGATA Array at Legnaro

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Study of the γ decay of high-lying states in208Pb via inelastic scattering of17O ions

Cited by 7 publications

References 49 publications

Dipole excitations via isoscalar probes: The splitting of the pygmy dipole resonance in124Sn

Dipole excitations via isoscalar probes: The splitting of the pygmy dipole resonance in124Sn

Nuclear Structure aspects of gamma decay from giant resonances

Nuclear Structure Studies with the AGATA Array at Legnaro

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Product

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Study of the γ decay of high-lying states in²⁰⁸Pb via inelastic scattering of¹⁷O ions