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National Superconducting
Cyclotron Laboratory

Alexandra Gade
Alexandra Gade
NSCL Chief Scientist, Professor of Physics
Experimental Nuclear Physics
PhD, Physics, University of Cologne 2002
Joined NSCL in April 2002
Phone gade at nscl.msu.edu
Fax (517) 908-7441
Office 1014
gade at nscl.msu.edu

Alexandra Gade

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The focus of my research is the structure of the atomic nucleus in the regime of very unbalanced proton and neutron numbers. Short-lived, radioactive nuclei that contain many more neutrons than protons often reveal surprising properties: Their shape and excitation pattern as well as the energy and occupation of the nucleus’ quantum mechanical orbits by protons and neutrons is significantly altered as compared to stable nuclei. My group uses nuclear reactions to probe such changes in the nuclear structure. Since our nuclei of interest are short-lived and cannot be made into targets, the beam is made up of the nuclei of interest. We have at hand an arsenal of different reactions to learn about specific degrees of freedom. These include scattering as well as reactions that remove or add a nucleon to the beam. The experimental challenge now is two-fold: We have to identify all reaction residues and characterize their properties, such as excitation patterns, for example.

For this, we use charged-particle and γ-ray detection techniques. The particle detection is most often performed with the S800 Spectrograph or with silicon detectors. Our group specializes on the crucial γ-ray spectroscopy aspect. Gamma-ray detection performed with the GRETINA, SeGA, or CAESAR arrays placed around the reaction target tells us if a given reaction led to an excited state. The energy of the detected γ ray measures the energy difference between two nuclear states and its intensity tells us how likely the state was populated in a reaction. A particular challenge is that the γ rays are emitted by nuclei traveling at up to 40% of the speed of flight. Consequently, they are Doppler-shifted and it requires knowledge of the emitter’s velocity and the γ ray’s emission angle to tease out the precise energy of a γ ray from the data. This is displayed in the figure below, showing what we detect in the laboratory (lower panel) and finally the precisely Doppler-reconstructed energy that informs about the energy of the first excited state in the short-lived nucleus 60Ti.

The results from those experiments are often surprising and reveal that exciting changes take place in the structure of exotic nuclei as compared to stable species. We collaborate closely with nuclear structure and reaction theorists. Our experimental input helps to unravel the driving forces behind the often spectacular modifications in nuclear structure and adds to the improvement of modern theories that are aimed to provide a model of the atomic nucleus with predictive power also in the exotic regime.

At any time, the projects available include:
• the analysis of new and exciting data
• large-scale detector simulations
• hands-on electronics and data acquisition
upgrades of our γ-ray detection systems
• or a combination of the above

gade

Reaction residues generated in the collision of a 38Si beam with a 9Be target. Energy loss versus flight time allows for unambiguous identification of all produced nuclei. The exotic nucleus of interest in this experiment was 36Mg which has twice as many neutrons as protons.

γ-ray energy spectrum detected in coincidence with 36Mg. The peak at 660 keV energy constitutes the first measurement of the energy of the first excited state in 36Mg, the heaviest Mg isotope studied with γ-ray spectroscopy to date.Save

Selected Publications

Is the Structure of 42Si Understood?, A. Gade et al, Phys. Rev. Lett. 122, 222501 (2019).

Commissioning of the LaBr3(Ce) detector array at the National Superconducting Cyclotron Laboratory, B. Longfellow et al., Nuclear Instrum. Methods Phys. Res. A 916, 141 (2019).

Localizing the Shape Transition in Neutron-Deficient Selenium, J. Henderson et al., Phys. Rev. Lett. 121, 082502 (2018).

Quadrupole collectivity beyond N=50 in neutron-rich Se and Kr isotopes, B. Elman et al., Phys. Rev. C 96, 044332 (2017).

Single-particle structure at N=29: The structure of 47Ar and first spectroscopy of 45S, A. Gade et al., Phys. Rev. C 93, 054315 (2016).