Prof. Dr. Kathrin Wimmer

Research group Prof. Dr. Kathrin Wimmer

Nuclear Collectivity Across the Nuclear Landscape

Atomic nuclei exhibit diverse collective behaviors depending on their proton–neutron composition, and the evolution of their B(E2) values reveals how shell structure, deformation, and magic numbers shape nuclear excitations.
Lifetimes of excited states

In in-beam γ-ray spectroscopy, the time-dependent Doppler shift—caused by changing ion velocity or emission angle—provides a precise clock to extract lifetimes of excited nuclear states in the picosecond to nanosecond range.
Improving Doppler Correction with Active Targets

LISA enhances lifetime measurements by pinpointing the reaction vertex within stacked active targets, enabling accurate velocity determination and sharper Doppler-corrected γ-ray spectra.
From Passive to Active Targets

By replacing a thick passive target with segmented active layers, LISA overcomes velocity-uncertainty broadening and dramatically improves resolution in experiments using low-intensity radioactive beams.
LISA: Precision Through Reaction-Point Localization

LISA’s ability to identify the exact target layer where a reaction occurs provides the correct β and α for Doppler correction, boosting both sensitivity and precision in measuring excited-state lifetimes.
Enhancing γ-Ray Resolution with LISA

By reducing effective target thickness and suppressing velocity-related broadening, LISA significantly improves γ-ray resolution in high-performance spectrometers like AGATA and GRETA, greatly boosting sensitivity to lifetimes of exotic nuclei.

Welcome to our research group

Atomic nuclei are a unique dual quantum liquid consisting of two types of fermions, protons and neutrons. Nuclei are relevant at many length and time scales in the Universe, from the size of a proton (∼10-15 m) to the size of a neutron star (∼103 m), and from just after the Big Bang (∼10-6 s) to the age of the Universe (13.8 ∙ 109 years). Depending on the number of protons and neutrons composing it, the nucleus can have vastly different properties. We are interested in the nuclear collectivity, i.e. how many nucleons participate in excitations. The evolution of collectivity in exotic atomic nuclei is deeply linked with shell evolution and magic numbers. Nuclei with extreme proton to neutron ratios have been explored in the recent years and the disappearance of classic shell closures is always associated with deformation and collective motion. A quantitative measure of the nuclear collectivity is the B(E2), shown here are the known data for the first quadrupole excitation of even-even nuclei [1]. This property maps out the nuclear landscape and shows the regions of nuclear deformation, shell and shape changes, and their deep connection to the magic numbers. Magic and doubly magic nuclei are dominated by single-particle behavior, B(E2) values only amount to a few Weisskopf units (a measure for how many nucleons participate in the excitation). Very collective nuclei have B(E2) values up to several hundred W.u. and the simple interpretation indicates that many nucleons participate in the excitation.

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