Advances in Radioactive Isotope Science

Probing the $N=152$ neutron shell gap by laser spectroscopy of fermium isotopes

6 juin 2023, 15:30

15m

oral contribution ground-state properties parallel session

Orateur

Mlle Jessica Warbinek (GSI Helmholtzzentrum für Schwerionenforschung GmbH; Johannes Gutenberg-Universität Mainz)

Description

Determining the limits of existence of the heaviest nuclides is a forefront topic in nuclear-physics research [1]. Nuclides with proton numbers $Z\geq$100 are stabilized by shell effects that retard spontaneous fission and they feature properties distinctly different from those of lighter nuclei. However, our understanding of such shell effects in the region of the heaviest elements is limited as predictions by state-of-the-art nuclear models are challenging and experimental studies are hampered by production capabilities. Recent mass measurements confirmed the location and the size of such a shell gap leading to an increased nuclear stability at neutron number $N=152$ in a region of strong prolate deformation [2,3].
Here, laser spectroscopy can serve as a powerful tool to extract experimental information on nuclear parameters such as the change in the mean-square charge radii and nuclear moments in a nuclear-model independent manner [4,5]. Access to the heaviest elements however is limited by production yields, their short half-lives and sparse information on atomic levels. The recent findings in the heavy actinide element nobelium ($Z=102$) with the RADRIS method paved the way for such observations [6,7].
New studies of fermium (Fm, $Z = 100$) isotopes allowed the determination of the isotope shift in an atomic transition for a long chain of eight isotopes ranging from the accelerator-produced $^{245}$Fm to the reactor-bred $^{257}$Fm. On-line and off-line laser spectroscopy techniques were significantly advanced to access these isotopes via various production methods down to minute production rates. The investigated isotopic chain spans across the known deformed shell gap at $N = 152$ allowing to probe its effect on changes in the mean-square charge radii. The experimental results revealing a discontinuity in the evolution of mean-square charge radii around the neutron shell gap will be discussed. These observations will trigger new developments in theoretical models which will eventually improve their predictive power towards the heaviest elements.
[1] W. Nazarewicz et al., Nat Phys 14, 537–541 (2018).
[2] E. Minaya Ramirez et al., Science 337, 1207–1210 (2012).
[3] C. Theisen et al., Nucl Phys A 944, 333–375 (2015).
[4] X. Yang et al., Prog Part Nucl Phys 129, 104005 (2023).
[5] M. Block et al., Prog Part Nucl Phys 116, 103834 (2021).
[6] M. Laatiaoui et al., Nature 538, 495–498 (2016).
[7] S. Raeder et al., Phys Rev Lett 120, 232503 (2018).

Documents de présentation

ARIS2023_JWarbinek.pptx