CE31 - Physique subatomique et astrophysique

Spectroscopy Electron Alpha in Silicon bOx couNter – SEASON

Submission summary

The study of atomic nuclei in their most extreme configurations, asymmetric in the proton (Z)/neutron number (N) ratio, in excitation energy or in mass, is a major direction of contemporary fundamental nuclear physics research. Pushed to its limits, a nucleus shows a characteristic behavior that reveals its underlying structure. Experimentally, these studies represent a major challenge in the region of heavy nuclei (HN, Z > 88) and superheavy nuclei (SHN, Z > 103) due to the low fusion-evaporation production cross sections involved, as well as due to the short lifetimes of the unstable reaction products. Therefore, few experimental results are available and the structure of these nuclei remains relatively unknown. Furthermore, the existing theoretical models do not reproduce the observations and they neither agree on the prediction of the potential « island of stability», nor on the limits of stability of nuclear matter. In this context, robust experimental data is necessary in order to serve as an anchor points for these models.

In the near future, thanks to high-intensity beams delivered by the « Super Separator Spectrometer (S3) » at GANIL/SPIRAL2, it will be possible to produce HN/SHN with intensities 15 to 20 times larger than those available at existing facilities. These new beams will offer the possibility to probe the structure of HN/SHN whose detailed spectroscopy is not yet accessible. At the S3 focal plane, the experimental set-up « low energy branch (LEB) » will allow performing laser-ionization spectroscopy of a large number of nuclei selected by S3. This technique provides an opportunity to deduce the properties of nuclei in their ground states or isomeric states, via atomic hyperfine structure and isotopic/isomeric shift measurements, independently from nuclear models. It provides a new approach for spectroscopic studies.

The goal of the SEASON project is the realization of HN/SHN spectroscopy, investigating ground or isomeric states, by applying a pioneering method: the comparison of observables measured by laser-ionization spectroscopy (atomic physics approach) with the results obtained by decay spectroscopy (nuclear physics method). This project is only possible by developing a detector that could take data from both approaches. Therefore, it is required to develop a detector that i) will count laser ionization products in order to measure the hyperfine structure and the isotopic/isomeric shift and ii) will perform simultaneously the decay spectroscopy (alpha, conversion electrons and gamma) of the implanted nuclei. This new experimental method will provide unprecedented constraints on the nuclear-structure models.

The second goal of the SEASON project is the realization of a first experiment at S3/LEB with the SEASON detector. We propose to perform laser-ionization spectroscopy of 225,226,227,228U isotopes, and simultaneously, their decay spectroscopy. This physics case is particularly interesting as several theoretical calculations predict strong octupole deformation in the region of neutron-deficient actinides. Given the difficulty to produce the required beams, laser-ionization spectroscopy has never been performed for these isotopes, and the data from standard nuclear physics experiments is scarce.

Beyond this first experiment, the entire S3/LEB community will be able to benefit from the dual experimental approach provided by SEASON to study the structure of a large number of HN/SHN, from Ac (Z = 89) to Rf (Z = 104).

Project coordination

Marine Vandebrouck (Institut de Recherche sur les lois Fondamentales de l'Univers)

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.

Partner

IRFU Institut de Recherche sur les lois Fondamentales de l'Univers

Help of the ANR 448,248 euros
Beginning and duration of the scientific project: - 48 Months

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