Pavlos Koseoglou

The production cross sections of neutron-rich nuclides near the N = 126 neutron shell closure have been measured for the elements ranging from tungsten ( Z = 74 ) to gold ( Z = 79 ) in the fragmentation of a 1000 MeV / u Pb 208 beam on a Be 9 target. Several cross sections, namely those for W 196 − 199 , Re 199 − 201 , and Os 202 − 203 , were determined for the first time with this projectile-target combination. The results are compared with the predictions of several nuclear reaction models and semiempirical parametrizations; special attention is devoted to multiple proton-removal channels and the formation of nuclides with neutron number N = 127 .

Three-neutron emission from He 7 has been directly measured for the first time, following neutron knockout from a He 8 beam at 156 MeV/nucleon. A resonancelike structure at 2.08(4) MeV above the He 4 + 3 n threshold [ E x = 2.68 ( 4 ) MeV] with a width of 3.9(2) MeV was observed and deduced to arise predominately from the predicted J π = 3 / 2 2 − level. The three-neutron invariant-mass spectrum was reconstructed and found to peak at around 1 MeV and could, through complete simulations incorporating neutron-neutron correlations, be very well described by the sequential decay of He * 7 via the 2 1 + excited state of He 6 . No evidence was found for any significant three-neutron correlations beyond those expected from well-established two-body interactions, including a trineutron resonance.

The weak binding and spatially extended neutron densities characteristic of drip-line nuclei give rise to a distinctive low-energy dipole response. The drip-line nucleus He 8 is the most neutron-rich bound nucleus with a mass-to-charge ratio of A / Z = 4 . We measure the dipole response of He 8 , including for the first time the four-neutron decay channel. A total dipole strength of ∑ B ( E 1 ) ( E * < 15 MeV ) = 0.95 ( 16 ) e 2 fm 2 and a dipole polarizability of α D = 0.61 ( 1 ) fm 3 are extracted from the differential Coulomb-excitation cross section and compared to state-of-the-art theoretical calculations employing coupled cluster and three-body approaches. We find that the dipole continuum is dominated, even at high excitation energies well above the 4 n decay threshold, by two-neutron emission, pointing to a He 6 + 2 n structure of the excited dipole mode. No indication was found for a 4 n final-state correlation, while pronounced n n and He 6 − n final-state correlations are apparent.

Even-even Yb and W isotopes around the N=104 mid-shell region are known to present deformation. The ground-band states of these nuclei are well described by the SU(3) symmetry, indicating a rigid-rotor character. Excited states of even-even isotopes in the region, namely 176Yb and 182W, were populated through Coulomb excitation and fusion-evaporation reactions, in an experiment performed at IFIN-HH in Măgurele, Romania. The gamma-spectroscopy of these nuclei will be presented in this contribution. Additionally, gamma spectroscopy results for the even-odd 177Yb nucleus, populated by the 1n-transfer reaction mechanism, will be presented. Contradictory to the collective description of the ground-band excitations in 176Yb and 182W isotopes, the excited states of this nucleus can be described by single-particle excitations. The gamma-spectroscopy analysis of this data contributes to the evaluation of the available data in this mass region, while ongoing work is expected to provide further insights for the nuclear structure of these rare-earth isotopes.

The Yb isotopes near the N=104 mid-shell region show a transition from spherical to well-deformed, rigid-rotor-like, structures. The 178Yb isotope (the most neutron-rich Yb isotope with measured excited states) shows signs of high deformation. A γ-spectroscopy experiment was conducted in the 10 MV FN Tandem accelerator of the Institut für Kernphysik at the University of Cologne to study 178Yb and the deformation evolution in the isotopic chain. The 176Yb(18O,16O)178Yb 2-neutron-transfer reaction was used to populate excited states in the isotope of interest. In this proceedings contribution the study of the excitation function of this 2-neutron-transfer reaction, which was measured across a range of beam energies, both below and above the Coulomb barrier, will be presented. Additionally, the study of the 176Yb(18O,4n)190Pt fusion-evaporation reaction occurring will also be discussed.

In this work a collective Hamiltonian based on relativistic energy density functional calculations has been used to study the basic spectroscopic properties of Er and Yb isotopes with 82 < 𝑁 < 114. Starting from a series of shape constrained calculations, we build a Bohr-type Hamiltonian the diagonalisation of which gives the collective excitations and transition probabilities. We are thus able to follow the transition of shapes, which is established through projected energy surfaces and specific spectroscopic quantities such as energy ratios and the structure of the low lying excited states.

The isotopes of Tellurium are located near the stability line on the isotopic chart, making them important for study in the context of nuclear theory and in terms of applications. In this work, we present a study of the radioactive decay chains of Tellurium isotopes with mass numbers 117 and 115, aiming to investigate their ground-state half-lives as determined from an experiment conducted at the 9 MV Tandem accelerator at IFIN-HH in Romania. Key parts of this presentation are a novel approach used to extract the experimental half-life values, as well as its application to the experimental data obtained for the two Tellurium decay chains. A comparison of the results for the half-lives obtained with and without the application of this approach will also be presented to demonstrate its capabilities. The approach does not rely on any input from the literature, and it allows for a significant reduction in the uncertainties associated with the extracted half-life values, thus enhancing the reliability and precision of the results.

The Confined β-soft (CBS) rotor model provides a simple collective approach in the region between the spherical vibrator and the axially deformed rotor limit for axially symmetric prolate (γ≈0) shapes. Even-even isotopes of Ytterbium and Tungsten serve as a good testing ground for exploring fundamental aspects of nuclear structure, as their R4/2=E(4+)/E(2+) ratio lies between 2.9 and 3.333. In the present study, the CBS formalism is applied to calculate the energies of the ground-state band, the associated B(E2) transition rates and the β-band excitations, directly comparing these predictions to available experimental data. The results demonstrate that CBS succeeds in reproducing the observed spectra and transition strengths for the case of axially symmetric isotopes of Yb and W.