Isospin Character of Low-lying Pygmy Dipole States Probed via Inelastic Scattering of $^{17}$O

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

doi:10.5506/aphyspolb.46.501

Cited by 3 publications

(4 citation statements)

References 12 publications

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“…Moreover, following the procedure presented in [20], we could quantify the fraction of the isoscalar electric dipole Energy Weighted Sum Rule (EWSR) exhausted by the 1 − states. For each pygmy state one expects to obtain, using the above procedure [8], the same value of the isoscalar electric dipole EWSR, independently of the used input cross section data (α or p). Therefore, as a consistency check, the fraction of the isoscalar electric dipole EWSR was deduced by fitting the α scattering data with DWBA calculations and these deduced values were then used to calculate the proton cross section without any further normalisation.…”

Section: Data Analysis Results and Interpretationmentioning

confidence: 99%

“…It is important to note, however, that the nature of h e p y g m y 1 − states is mixed in terms of isospin. This is already experimentally established [4,8,9,10,11], even though the degree of collectivity of these states is not clarified yet. Interestingly, the importance of the PDR phenomenon is expected to increase right in nuclear systems characterized by extreme conditions of isospin (in exotic neutron-rich nuclei).…”

Section: Introductionmentioning

confidence: 82%

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The structure of low-lying 1⁻ states in ^90,94Zr from (α,α′γ) and (p,p′γ) reactions

Crespi

2023

J. Phys.: Conf. Ser.

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The low-lying dipole strength was investigated in 90,94 Zr via the (p,p′γ) reaction at 80 MeV and via the (α,α′γ) reaction at 130 MeV. These experiments were performed at the Research Center for Nuclear Physics (Osaka University) and made combined use of the high-resolution magnetic spectrometer Grand Raiden and the CAGRA HPGe gamma array. The comparison of our results with existing (γ,γ′) reaction data shows differences in the excitation patterns. In the present experimental conditions, in fact, both α and p probes are exciting the investigated 1− states mainly through the short-range nuclear force, expected to favour the population of surface excitations. Distorted Wave Born Approximation (DWBA) calculations were made using form factors built assuming specific transition densities, characterized by a strong neutron component at the nuclear surface and based on Random Phase Approximation (RPA). A combined analysis of the (α,α′γ) and (p,p′γ) data was performed to investigate the isoscalar character of the 1− states in 90,94Zr. Although an overall general consistency was obtained in the studied energy intervals, not all (p,p′γ) cross sections were well reproduced using the isoscalar strength deduced from (α,α′γ) data. This might suggest that the mixing of isoscalar and isovector components and the degree of collectivity are not the same for all the 1− states studied.

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Section: Data Analysis Results and Interpretationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 82%

The structure of low-lying 1⁻ states in ^90,94Zr from (α,α′γ) and (p,p′γ) reactions

Crespi

2023

J. Phys.: Conf. Ser.

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“…One milestone in the investigation of the PDR are experiments with isoscalar hadronic probes like α particles and 17 O ions. A structural splitting of the low-lying E1 strength in numerous nuclei was observed in (α, α γ ) [45][46][47] and ( 17 O, 17 O γ ) [19,48,49] reactions using either singlecrystal HPGe or the highly-segmented tracking detector array AGATA for the coincident γ ray detection. A prominent example is shown in Fig.…”

Section: Structure Of the Pygmy Dipole Resonancementioning

confidence: 99%

AGATA: Nuclear structure advancements with high-energy $$\gamma $$ rays

Camera¹,

Isaak²,

Maj³

et al. 2023

Eur. Phys. J. A

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High-energy $$\gamma $$ γ rays are emitted either in the decay of nuclear discrete states (generally located in the proximity of the particle-emission threshold) or in the electromagnetic decay of collective states. The branching ratio is rather small, therefore in alternative/coincidence with high-energy $$\gamma $$ γ rays one could have neutron or charged-particle emission. The precise measurement of these branching ratios allows a more comprehensive description of the nucleus and, in particular, the selection of the nuclear models which better describes the interplay between the different acting forces and couplings. In the case of the electromagnetic decay of collective states, the precise identification of the populated low-lying states allows the measurement of their wave-function and/or of their ‘bulk’ properties. This information provides, also in this case, a stringent test for the nuclear models. In both cases, to compensate these small branching ratio, a large number of detectors and an accurate selection of a small region of the phase space are needed. AGATA is considered to constitute an optimal array for this kind of measurements. In fact, AGATA, because of its high granularity and its excellent energy resolution, can detect the high-energy $$\gamma $$ γ rays emitted in a specific decay path or associated to specific reaction channels, shapes, deformations. In the introduction, some details on the measurement of high-energy $$\gamma $$ γ rays using HPGe detector are discussed. The sections of this paper focus on the measurements of high-energy $$\gamma $$ γ rays to obtain the photon strength function, the nuclear level density and to identify extreme shapes in highly excited nuclei.

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“…This is where the β -decay studies can play a major role in the exploration of the PDR properties. Thanks to the selective population of precursor-like spin-parity excited states of the daughter nucleus and to the large Q β value of exotic neutronrich nuclei, the medium-spin PDR states can be accessible via β -decay, when they are hardly observable in conventional experiments [28][29][30][31][32][33]. Last but not least, in β -decay experiments the population of 2p2h multi-correlated [34,35] and collective-vibration states [36] is favored thanks to the complexities of the weak interaction process in the nuclear medium [35,[37][38][39] and global response of the nucleus afterwards.…”

mentioning

confidence: 99%

First evidence for non 1− pygmy dipole resonance in neutron-rich nuclei

Li,

Ponomarev,

Harakeh

et al. 2023

Preprint

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We predict the existence of medium spin PDR and find experimental evidence in 80Ge using β-decay of 80Ga. This nucleus was produced in the photo-fission of 238U. A hybrid γ-ray spectrometer was developed using a plastic detector for β-tagging, HPGe detectors for low-energy γ rays detection and phoswich detectors of PARIS for high-energy γ rays. The low-high energy coincidence spectrum shows two peaks at 7181(53) and 7337(53) keV in the β-decay of the 80mGa isomeric state only, in coincidence with the 21+ → 0+ transition of 80Ge. Combined with decay information, electric dipole character (E1) were assigned to these γ rays which de-excite 7.84 MeV and 7.996 MeV states. Based on this fact and the comparison with theoretical calculations, we conclude that these enhanced E1 transitions are driven by neutron-skin oscillation of 80Ge. The oscillation is triggered by a conversion of a deeply-bound neutron from the Z=N=28 proton-neutron saturated core into a proton in the Fermi surface. These results provide an evidence for a PDR state with spin different from 1− and built on a low-energy excited state. Consequently, it extends the PDR’s boundary along spin dimension for the first time and provides experimental data for testing the validity of the Brink-Axel hypothesis in the PDR region.

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Isospin Character of Low-lying Pygmy Dipole States Probed via Inelastic Scattering of $^{17}$O

Cited by 3 publications

References 12 publications

The structure of low-lying 1⁻ states in ^90,94Zr from (α,α′γ) and (p,p′γ) reactions

The structure of low-lying 1⁻ states in ^90,94Zr from (α,α′γ) and (p,p′γ) reactions

AGATA: Nuclear structure advancements with high-energy $$\gamma $$ rays

First evidence for non 1− pygmy dipole resonance in neutron-rich nuclei

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Isospin Character of Low-lying Pygmy Dipole States Probed via Inelastic Scattering of $^{17}$O

Cited by 3 publications

References 12 publications

The structure of low-lying 1− states in 90,94Zr from (α,α′γ) and (p,p′γ) reactions

The structure of low-lying 1− states in 90,94Zr from (α,α′γ) and (p,p′γ) reactions

AGATA: Nuclear structure advancements with high-energy $$\gamma $$ rays

First evidence for non 1− pygmy dipole resonance in neutron-rich nuclei

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Product

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The structure of low-lying 1⁻ states in ^90,94Zr from (α,α′γ) and (p,p′γ) reactions

The structure of low-lying 1⁻ states in ^90,94Zr from (α,α′γ) and (p,p′γ) reactions