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National Superconducting
Cyclotron Laboratory

Hironori Iwasaki
Hironori Iwasaki
Associate Professor
Experimental Nuclear Physics
PhD, Physics, University of Tokyo, 2001
Joined NSCL in September 2009
Phone (517) 908-7660
Fax (517) 353-5967
Office 1012
iwasaki at nscl.msu.edu

Hironori Iwasaki

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My research focuses on lifetime measurements and spectroscopy with rare isotope beams. Unstable or exotic nuclei produced as rare isotope beams have unusual proton-to-neutron ratios. They often show surprising phenomena such as exotic shapes and collective motions. We provide precise and accurate data and compare them with theoretical predictions. In this way, we understand the structure and dynamics characteristic of exotic nuclei.

At NSCL, my group has performed excited-state lifetime measurements based on gamma-ray spectroscopy. Lifetimes of bound excited states determine transition probabilities between the states. Such data provide sensitive probes for anomalies in the nuclear structure. For instance, one can observe halo neutrons that move in spatially extended orbits. For unbound levels, lifetimes can be related to the resonance widths, which play important roles in the stability of extreme quantum systems as well as in nuclear reaction rates of astrophysical interest.

We have recently developed a new plunger device TRIPLEX (TRIple PLunger for EXotic beams, Fig.1) dedicated for the recoil-distance Doppler-shift lifetime measurements. The device uses three thin metal foils separated by very precise distances. In this approach, Coulomb excitation or knockout reactions are used to populate excited states in exotic, projectile-like reaction residues that decay in flight after traveling a distance related to its lifetime. Two degraders positioned downstream of the target reduce the velocity of the ion. As a consequence, gamma-rays emitted behind each foil have different Doppler shifts. The lifetime of the state can be determined using relative gamma-ray yields measured at different foil separations. Figure 2 shows an example of experimental results obtained for 74Kr. Lifetime information can confirm the exotic structure of 74Kr, where different nuclear shapes coexist in its ground state.

In my group, graduate students 1) develop new experimental techniques in lifetime measurements using fast and reaccelerated rare isotope beams and 2) analyze data and interpret physics results from experiments. Students also work on hands-on projects including the preparation and operation of the TRIPLEX device and the development of new detectors such as radiation-hard diamond detectors and associated data acquisition system.

TRIPLEX

(1) The TRIPLEX plunger device.

iwasaki

(2) Energy spectrum of g rays measured in coincidence with 74Kr. The spectrum shows the fast (f), reduced (r), and slow (s) components in the recoil-distance Doppler-shift measurement, indicating sensitivities to different lifetimes of the excited states.

Selected Publications

Enhanced Electric Dipole Strength for the Weakly Bound States in 27Ne; C. Loelius, N. Kobayashi, H. Iwasaki, et al., Phys. Rev. Lett. 121, 262501 (2018).

Lifetime Measurement of the 2+ state in 74Rb and isospin properties of quadrupole transition strengths at N=Z; C. Morse, H. Iwasaki, et al., Phys. Lett. B 787 (2018).

Lifetime Measurement and triple coexistence band structure in 43S; T. Mijatovic’, N. Kobayashi, H. Iwasaki, et al., Phys. Rev. Lett. 121, 012501 (2018).

The TRIple PLunger for EXotic beams TRIPLEX for excited-state lifetime measurement studies on rare isotope; H. Iwasaki, A. Dewald, T. Braunroth, et al., Nucl. Instrum. And Methods in Phys. Res. A 806, 123 (2016).

Evolution of collectivity in 72Kr; evidence for rapid shape transition; H. Iwasaki, A. Lemasson, et al., Phys. Rev. Lett. 112 (2014) 142502.