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Shape Coexistence and Collectivity in Atomic Nuclei

Final Report Summary - SPEDE (Shape Coexistence and Collectivity in Atomic Nuclei)

In the atomic nucleus, the interplay between single-particle motion, collectivity and pairing is seen as a rich tapestry of coexisting nuclear shapes and exotic excitations. For verifying and more detailed understanding of the shape coexistence phenomenon it is important to measure transition probabilities between the coexisting nuclear states.

In the endeavour to understand the nuclear structure and related interesting phenomena, in-beam gamma-ray and electron spectrometers have been important tools. However, a gamma-ray or an electron spectrometer alone can provide only partial information of nuclear de-excitation processes. Moreover, electron spectroscopy with radioactive ion beams (RIBS), with very few exceptions, has not been exploited at all.

The research objectives of the SPEDE project are:
1) Initiate an electron spectroscopy campaign by performing simultaneous in-beam conversion electron-γ-ray spectroscopy in the Accelerator Laboratory of University of Jyväskylä (JYFL).
2) Develop in-beam conversion electron-γ-ray spectroscopy techniques, for the first time, for complementary experiments with RIBs at REX-ISOLDE (and for future HIE-ISOLDE).

The scientific aim of the present proposal is to extend the studies of shape coexistence in exotic nuclei by employing novel methods of in-beam conversion electron spectroscopy to investigations of electric monopole transitions (E0) and other highly converted transitions. Such studies have been carried out for nuclei close to the stability line but so far only very few attempts have been made for exotic nuclei close to the drip lines, especially when employing RIBs.

Since the beginning of the project, the SPEDE spectrometer has been brought from a design table to a working device. This effort includes mechanical and electronics design, construction of parts, assembly of the spectrometer and throughout testing (such as vacuum, electronics, cryogenics, safety and operation in general).

The main result obtained so far is a working in-beam conversion electron spectrometer that employs a novel concept. The SPEDE spectrometer has been tested in-beam in real running conditions, and for the first time conversion electron spectroscopy has been possible at the target position, where the background radiation is high.

When combined with the MINIBALL spectrometer at HIE-ISOLDE, CERN, the SPEDE spectrometer will provide a complementary, but essential data to understand the shape coexistence, collectivity and mixing of different intrinsic proton-neutron configurations in the neutron-deficient Pb region.

The proposed project is carried out at JYFL and provides a step towards a professional researcher and enables to diversify the physics interests of the Fellow. The Researcher has managed a large international collaboration and has had a key role in the JYFL-ISOLDE collaboration with a scope of obtaining a tenure track position at JYFL. Such researchers are also needed in future RIBs facilities. Discussions on securing a permanent position for the Researcher at the host institute are under way.