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

Kei Minamisono

What is the most fundamental property of a nucleus? Arguably, the size/shape of the nucleus is one of them. My current research interests is to determine the size, shape or radius of a rare nucleus that occurs around the existence limit of the nuclei. The size of a nucleus tells us how nucleons are distributed inside a nucleus. It is essential to gain critical insights into the driving nuclear forces of structural changes compared to stable nuclei surrounding us.

Here is one example: the radii of very light mass, proton-rich calcium isotopes, which is shown in the figure. 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! Nuclear scientists consider the chain of Ca radii as a “text book” example of how the nuclear structure effect emerges in the radii, and is challenging nuclear theories. For such system, we determined radii of proton-rich Ca isotopes. They turned out to be very compact and surprisingly small compared with the previous theory, adding a new puzzle. An improved theory had to be developed, correctly taking into account the weak binding of protons, that is the coupling with the proton continuum. The improved theory now successfully explains the general trend of radii from proton-rich 36Ca to neutron-rich 52Ca isotopes.

We perform experiments at the BEam COoling and LAser spectroscopy (BECOLA) facility at NSCL/FRIB. We illuminate laser light on a fast atom beam and detect fluorescence from the perturbed atom due to the interplay between the orbital electron and nucleus. The fluorescence contains information about the size of a nucleus. Technical development is another essential aspect of our group to get to rarest isotopes for the radius measurements. For example, developments of laser techniques and production of stable isotopes are critical. Among others, the Collinear Resonance laser Ionization Spectroscopy (CRIS) is planned to be developed. Multiple laser light will be illuminated to an atom beam to selectively ionize the atom, which is detected as a resonance signal. Highly sensitive measurements will be enabled to address the rarest isotopes.

Students in my group will have training opportunities to gain hands-on experience in running laser spectroscopy experiments for nuclear structure studies. We run laser spectroscopy experiment online (with radioactive beams) as well as offline (with stable beams produced locally). The experimental system includes but not limited to operation of various laser systems (CW and pulsed, and lots of alignment), the ion beam production (operation) from offline ion sources, the ion-beam transport, the data acquisition system, and the analysis/interpretation of obtained data.

Ca isotopes

Charge radii of calcium isotopes. Our data is shown in solid red circles. Previous and improved theories are shown in solid gray and yellow lines, respectively.

Selected Publications

Implications of the 36Ca-36S and 38Ca-38Ar difference in mirror charge radii on the neutron matter equation of state, B. A. Brown et al., Phys. Rev. Research 2, 022035(R) (2020).

Ground-state electromagnetic moments of 37Ca, A. Klose et al., Phys. Rev. C 99, 061301(R) (2019).

 Proton superfluidity and charge radii in proton-rich calcium isotopes, A. J. Miller et al., Nature Physics 15, 432 (2019).

 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).