Collectivity at the prolate-oblate transition:the 2₁⁺ lifetime of ¹⁹⁰W

The neutron-rich rare isotope 190W is discussed as a candidate for a prolate-oblate transitional nucleus with maximum γ-softness. The collectivity of this isotope is assessed for the first time by the measurement of the reduced E2 transition probability of its first 2+ state to the ground state. The experiment employed the FAst TIming Array (FATIMA), comprised of 36 LaBr3(Ce) scintillators, which was part of the DESPEC setup at GSI, Darmstadt. The 41+ and 21+ states of 190W were populated subsequently to the decay of its 127(12) μs isomeric Jπ  = 10- state. The mean lifetime of the 21+ state was determined to be τ = 274(28) ps, which corresponds to a B(E2; 21+ → 01+) value of 95(10) W.u. The results motivated a revision of previous calculations within an energy-density functional-based interacting boson model-2 approach, yielding E2 transition properties and spectroscopic quadrupole moments for tungsten isotopes. From comparison to theory, the new data suggest that 190W is at the transition from prolate to oblate structure along the W isotopic chain, which had previously been discussed as a nuclear shape-phase transition

Decay studies in the A ∼ 225 Po-Fr region from the DESPEC campaign at GSI in 2021

The HISPEC-DESPEC collaboration aims at investigating the structure of exotic nuclei formed in fragmentation reactions with decay spectroscopy measurements, as part of the FAIR Phase-0 campaign at GSI. This paper reports on first results of an experiment performed in spring 2021, with a focus on β-decay studies in the Po-Fr nuclei in the 220 <A< 230 island of octupole deformation exploiting the DESPEC setup. Ion-beta correlations and fast-timing techniques are being employed, giving an insight into this difficult-to-reach region

Sub-barrier fusion in C12+Mg26,24 : Hindrance and oscillations

Background: The existence of fusion hindrance in the light heavy-ion systems of astrophysical interest is not well established, so investigating slightly heavier cases may allow a reliable extrapolation towards the lighter ones. The recent observation of a very high hindrance threshold in 12 C + 24 Mg (with a positive Q value for fusion) at σfus 0.75 mb, misses a valid interpretation within current theoretical models. Purpose: Our aim has been to search evidence for fusion hindrances in the nearby system 12 C + 26 Mg also having Qfus > 0, and to obtain information on the underlying physics from a comparison of the two cases and from coupled-channels calculations. Methods: The experiment was performed in inverse kinematics using the 26 Mg beam from the XTU Tandem accelerator of Laboratori Nazionali di Legnaro (LNL). The targets were thin 12 C evaporations isotopically enriched to 99.9%. The fusion-evaporation residues were detected at small angles by a E - E -ToF detector telescope following an electrostatic beam deflector. Results: The fusion excitation function of 12 C + 26 Mg has been measured down to ≈5 μb. The astrophysical S factor shows a maximum at an energy where the cross section is ≈0.03 mb, significantly lower than for 12 C + 24 Mg. This difference is confirmed by the comparison of the two S factors. coupled channel calculations give a good account of the data, but they overpredict the cross sections below ≈0.03 mb. The logarithmic slopes of the two excitation functions are superimposable to a large extent, with visible oscillations, more noticeable for 12 C + 24 Mg. Conclusions: The hindrance phenomenon is clearly observed in 12 C + 26 Mg. The difference between the corresponding threshold energies for 12 C + 24,26 Mg might (only qualitatively) be attributed to the α-like structure of 24 Mg. In the Jiang’s phenomenological systematics, the different behaviors of 12 C + 24,26 Mg make the situation more complex, and call into question the extrapolation procedure toward the lighter systems of astrophysical interest

Nuclear structure advancements with multi-nucleon transfer reactions

International audienceMulti-Nucleon Transfer (MNT) reactions have been used for decades as a reaction mechanism, in order to populate excited states in nuclei far from stability and to perform nuclear structure studies. Nevertheless, the development of set-ups involving high acceptance tracking magnetic spectrometers (mainly existing in Europe), coupled with the Advanced GAmma Tracking Array (AGATA) opens new possibilities, especially if they are used in conjunction with high-intensity stable beams or ISOL RIBs. In this article, we will discuss the capabilities of such set-ups aiming at different goals, including complete information in high-resolution spectroscopy as well as lifetime measurements

GALTRACE: A highly segmented silicon detector array for charged particle spectroscopy and discrimination

GALTRACE is an array of segmented silicon detectors specifically built to work as an ancillary of the GALILEO γ-ray spectrometer at Legnaro National Laboratory of INFN. GALTRACE consists of four telescopic ΔE-E detectors which allow discriminating light charged particles also via pulse-shape analysis techniques. The good angular and energy resolutions, together with particle discrimination capabilities, make GALTRACE suitable for experiments where coincidences with specific emitted particles allow for the selection of reaction channels with very low cross section. The first in-beam experiment is reported here, aiming at identifying a narrow resonance, near-proton-threshold state in 11B, currently under discussion

GALTRACE: A highly segmented silicon detector array for charged particle spectroscopy and discrimination

International audienceGALTRACE is an array of segmented silicon detectors specificallybuilt to work as an ancillary of the GALILEO γ-ray spectrometer at Legnaro Na-tional Laboratory of INFN. GALTRACE consists of four telescopic ΔE-E detec-tors which allow discriminating light charged particles also via pulse-shape anal-ysis techniques. The good angular and energy resolutions, together with particlediscrimination capabilities, make GALTRACE suitable for experiments where coin-cidences with specific emitted particles allow for the selection of reaction channelswith very low cross section. The first in-beam experiment is reported here, aiming atidentifying a narrow resonance, near-proton-threshold state in 11 B, currently underdiscussion

Decay studies in the A ∼ 225 Po-Fr region from the DESPEC campaign at GSI in 2021

The HISPEC-DESPEC collaboration aims at investigating the structure of exotic nuclei formed in fragmentation reactions with decay spectroscopy measurements, as part of the FAIR Phase-0 campaign at GSI. This paper reports on first results of an experiment performed in spring 2021, with a focus on β-decay studies in the Po-Fr nuclei in the 220 &lt; A &lt; 230 island of octupole deformation exploiting the DESPEC setup. Ion-beta correlations and fast-timing techniques are being employed, giving an insight into this difficult-to-reach region

Decay studies in the A∼225 Po-Fr region from the DESPEC campaign at GSI in 2021

The HISPEC-DESPEC collaboration aims at investigating the structure of exotic nuclei formed in fragmentation reactions with decay spectroscopy measurements, as part of the FAIR Phase-0 campaign at GSI. This paper reports on first results of an experiment performed in spring 2021, with a focus on β-decay studies in the Po-Fr nuclei in the 220 <A< 230 island of octupole deformation exploiting the DESPEC setup. Ion-beta correlations and fast-timing techniques are being employed, giving an insight into this difficult-to-reach region