Our research has focused on spectroscopy of exotic nuclei far from stability. Unstable nuclei with very unusual proton-to-neutron ratios, called as "exotic nuclei", often show surprising phenomena, presenting important challenges for our understanding of atomic nuclei. The goal of present-day nuclear physics is to establish the unified understanding of nuclear structure for stable and exotic nuclei, by exploring the isospin degree-of-freedom of the shell structure and collective properties of nuclei. The physics outputs thus serve as vigorous tests for modern nuclear theories, as well as provide answers to questions concerning the nature of neutron stars and the origin of the elements in the Universe. Nuclear structure information can also be used to make tests of fundamental symmetries that describe the weak and strong forces in nature.

At NSCL, our group performs in-beam gamma and particle spectroscopy with rare isotope beams, with an emphasis on lifetime measurements for nuclear levels. Lifetimes for bound levels are closely related to transition probabilities between the relevant states, which provide sensitive probes for anomalies in structure of exotic nuclei, for example, shape coexistence, changes of magic numbers, and proton-neutron decoupling phenomena, and so on. For unbound levels, lifetimes can be associated with the energy uncertainties to be measured as the resonance widths, which play important roles in the stability of extreme quantum systems as well as in nuclear reaction rates of astrophysical interest.

Challenges in experimental studies for level lifetime measurements are to develop methodology and detection system, which are suitable for the use with rare isotope beams. Typical level lifetimes range from 1 nano (10^-9) to 1 femto seconds (10^-15) for bound levels, and for resonances, lifetimes can be even 1 zepto second (10^-21). In Figure, a so-called plunger device for the Recoil Distance Doppler-shift Method (RDDM) is shown, which we are developing to measure nuclear level lifetimes in the order of 1 pico second (10^-12). Experimental programs are being performed and planned at NSCL with fast and re-accelerated rare isotope beams.