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National Superconducting
Cyclotron Laboratory

Kei Minamisono
Kei Minamisono
Research Senior Physicist and Adj. Professor of Physics
Experimental Nuclear Physics
PhD, Physics, Osaka University, 1999
Joined NSCL in October 2004
Phone (517) 908-7145
Fax (517) 353-5967
Office 1047
minamiso at nscl.msu.edu

Kei Minamisono

One of my current research interests is to determine fundamental properties of radioactive nuclei away from the stable isotopes towards the nucleon driplines. In particular I am interested in electromagnetic moments and charge radii, which are sensitive to the configuration of nucleons inside a nucleus and the nuclear shape/size. Experimental determination of these properties are essential to gain critical insights into the driving force of the structural change in rare isotopes by comparison with state-of-the-art theories.  

Laser assisted techniques are ued to measure hyperfine spectra, form which electromagnetic moments and charge radii can be deduced. Hyperfine interaction is an interplay between nuclear and atomic spins/angular momenta, perturbs atomic energy levels and results in a hyperfine structure, which can be probed for example using laser-resonant fluorescence measurements.

Such experimental techniques are available at the BEam COoling and LAser spectroscopy (BECOLA) facility at NSCL. High precision/resolution laser systems and a detection system with great sensitivity are required to resolve hyperfine structure of rare isotopes, which is only available with a small amount. Technical development is another essential aspect of our group to enhance overall sensitivity, leading to extension of the reach of radioactive isotopes. Some of ongoing efforts include manipulation of atomic population in an RFQ ion trap, resonant laser ionization spectroscopy and offline production of stable-isotope beams for studies of laser excitation schemes.

Ca isotopes

Charge radii of calcium isotopes are shown. Experimental charge radii show a very intricate pattern as more neutrons are added (the 48Ca nucleus, for example has almost the same radius as 40Ca with eight more neutrons are added!). The chain of Ca radii has been considered as a "text book" example of how the nuclear structure effect emerges in the radii, and challenging nuclear theories. For such system, we determined radii of proton-rich Ca isotopes (solid red circles). They turned out to be very compact and surprisingly small compared with the previous theory. An improved theory, correctly taking into account the weak binding of protons, that is the coupling with the proton continuum, successfully explains not only the proton-rich but also the neutron rich Ca isotopes.  

Selected Publications

Proton superfluidity and charge radii in proton-rich calcium isotopes,
A. J. Miller et al., Nature Physics (2019), https://doi.org/10.1038/s41567-019-0416-9.

First determination of ground state electromagnetic moments of 53Fe,
A. J. Miller et al., Phys. Rev. C 96, 054314 (2017).

Charge radii of neutron deficient 52,53Fe produced by projectile fragmentation,
K. Minamisono, et al., Phys. Rev. Lett. 117, 252501 (2016).

Population distribution subsequent to charge exchange of 29.85 keV Ni+ on sodium vapor, 
C. A. Ryder et al., Spectrochimica Acta Part B 113, 16 (2015).

Charge radii of neutron-deficient 36K and 37K, 
D. M. Rossi et al., Phys. Rev. C 92, 014305 (2015).