BEGIN:VCALENDAR VERSION:2.0 PRODID:-//CERN//INDICO//EN BEGIN:VEVENT SUMMARY:Emergence of triaxiality in 74Se from electric monopole transition strengths DTSTART;VALUE=DATE-TIME:20231130T101000Z DTEND;VALUE=DATE-TIME:20231130T102500Z DTSTAMP;VALUE=DATE-TIME:20260811T105524Z UID:indico-contribution-3377@indico.tlabs.ac.za DESCRIPTION:Speakers: Naomi Marchini (University of Florence - INFN Floren ce section)\nThe 2+2 state in non-doubly-magic\, even-even nuclei is commo nly interpreted as due to a collective excitation. In the vibrational and rotational limits\, this state originates from vibrations around the groun d-state shape. Even though these basic paradigms are known to represent on ly a first-order approximation of the nuclear structure\, they are still u sed for classifying isotopes throughout the chart of the nuclides and as a basis for more complex theoretical approaches. Nevertheless\, since the a ppearance of low-energy nuclear vibrations has been debated in the recent literature\, the possible vibrational interpretation of the 2+2\nstate als o needs to be carefully reanalysed.\nMonopole transitions (E0) are an idea l tool to investigate nuclear structure because they are related to the ra dial distribution of the electric charge inside the nucleus. Therefore\, m onopole transition strengths ρ2(E0) are sensitive to changes in the shape of the nuclear states. In particular\, this observable is zero if the sha pe of the two involved states is the same and/or if there is no configurat ion mixing between their wavefunctions. Noteworthy\,\nthe ρ2(E0) value be tween the first two 2+ states is zero in both the vibrational and axially- symmetric rotational limits. A surprising result has been recently obtaine d in the Ni isotopic chain\, where large ρ2(E0\; 2+2 → 2+1) values have been measured. Apart from simple models\, a more sophisticated method bas ed on the shell model was also applied to explain these large ρ2(E0) valu es\, unsuccessfully.\nSelenium isotopes are thought to be collective in th eir low-lying structure. Which kind of collectivity\, however\, is still a matter of debate. A nearly spherical-vibrational scenario was suggested f or 74Se in a recent β-decay study. The anomalous low energy of the 0+2 st ate\, which is a member of the two-phonon multiplet in this case\, was exp lained as due to the mixing between the 0+2 state and the intruder\, stron gly-deformed 03 state. While this interpretation explains several observab les in 74Se\, others are not reproduced. If this picture is correct\, the ρ2(E0\; 2 +2 → 2 1 ) value should be negligible and the ρ (E0\; 0 3 → 0 2 ) value should be large. Noteworthy\, former studies identified th e 0+2 state as another shape-coexisting state\, and the 2+ state as the ba nd-head of a γ-band.\nGiven the most recent suggestions regarding the app earance of multiple-shape coexistence in the neighbouring Ni isotopes\, an d the emerging role of triaxiality in the nearby 76 Se and the close Ge an d Zn isotopes\, further investigation in 74Se is required.\nThis contribut ion presents new experimental results regarding internal conversion coeffi cients and monopole transition strengths in 74Se. A large ρ2(E0\; 2 +\n2 → 2 1 ) value has been measured\, with a magnitude comparable to those i n the close Ni isotopes\, while the ρ2(E0\; 0 +3 → 0 2 ) value has been deduced to be small. Also\, for the first time microscopic Beyond-Mean-Fi eld (BMF) calculations for 74 Se will be present\, and the role of triaxia lity in this isotope discussed.\n\nhttps://indico.tlabs.ac.za/event/119/co ntributions/3377/ LOCATION: URL:https://indico.tlabs.ac.za/event/119/contributions/3377/ END:VEVENT END:VCALENDAR