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Physics & Astronomy Department
Vanderbilt University
PMB 401807
2401 Vanderbilt Place
Nashville, TN 37240-1807

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Experimental Nuclear Physics: Nuclear Structure

Faculty: J. H. Hamilton and A. V. Ramayya
Senior Research Associates: J. K. Hwang, Y. X. Luo
Graduate Students: S. Liu, N. Brewer

Low energy nuclear physics at Vanderbilt University addresses the structure of atomic nuclei, with special emphasis on both proton and neutron rich nuclei far from the stable ones found in nature.

Many of the intellectual challenges that confront us today can only be answered with forefront accelerators, sophisticated detector arrays, and high-powered computers. At Vanderbilt the nuclear structure group produce nuclei out to the extremes including new neutron-rich nuclei and proton rich nuclei at the limits of stability and investigate their behavior at high excitation energies and angular momentum and their exotic decay modes and binding energies. For such studies, the group initiated a new generation Recoil Mass Spectrometer that was built at the Holifield Radioactive Ion Beam Facility (HRIBF) with a variety of sophisticated detectors developed for use with it.

Recent research has been carried out with heavy-ion accelerators and/or spontaneous fission sources at Oak Ridge National Laboratory, Argonne National Laboratory, Lawrence Berkeley Laboratory in US and Flerov Laboratory for Heavy Ion Reactions (Dubna, Russia).

Some of the discoveries by our group include (a) existence of spherical and deformed shapes in the same nucleus; (b) super-, hyper, and octupole deformation; (c) cold and hot binary and ternary fission modes; (d) many neutron rich isotopes; (e) proton radioactivities, (f) new deformed magic numbers at 38 and 60 and chiral doublet bands and wobbling motion in triaxial nuclei.

The Vanderbilt group is a member of the University Radioactive Beam Consortium (UNIRIB) at Oak Ridge National Laboratory. The university members and the three UNIRIB on-site staff and ORNL cooperate in research. The group has just completed a new detector station to study the decays of neutron-rich radioactive nuclei produced in the proton induced fission of uranium at the Holifield Radioactive Ion Beam Facility (HRIBF) at ORNL. The group just received a $1.8M grant to complete a new multipass time of flight separator spectrometer with resolution of one part in 200,000 - 400,000 (a factor of 20-40 better than any existing facility) to study presently-inaccessible, very neutron-rich nuclei produced with very low yields. Current research involves studies of neutron-rich nuclei around double magic 78Ni, alpha decay in the region just above 100Sn, and proton radioactivities at the proton dripline.

We continue to study neutron-rich nuclei produced in the spontaneous fission of 252Cf. We have identified new isotopes and significantly extending the level structure of over 100 nuclei in these studies. Two new experiments in 2010 with 252Cf will enable us to probe more deeply the fission process and extend our studies to still more neutron-rich nuclei. This work involves a cooperation with the Flerov Laboratory for Heavy Ion Research in Russia, Tsinghua University in Beijing, Lawrence Berkeley National Laboratory in California and other universities with Vanderbilt the group leader.

In August 2009, the Vanderbilt group became involved with the Flerov Laboratory, where new superheavy elements 114, 115, 116 and 118 were discovered, to synthesizing element 117. This work will continue in the future to synthesize elements 119 and 120, and other more neutron-rich nuclei. This cooperative work, that also includes Lawrence Livermore National Laboratory, makes use of targets made at ORNL and the 48Ca beam at the Flerov Laboratory. Graduate students and faculty will spend time in Russia working on these experiments.

The research group has an international reputation and regularly presents invited papers at international conferences (95 invited papers at 75 international conferences in 11 countries in the last five years). There are active collaborations with scientists from Oak Ridge National Laboratory, Argonne National Laboratory, Lawrence Berkeley and Livermore National Laboratories, Idaho National Laboratory, and members of the UNRIB Consortium of 12 major universities at ORNL in US and from Brazil, China, Germany, Italy, Poland, Romania, Russia and Slovakia. The research is supported by the U.S. Department of Energy.

Graduate students working in the group receive financial support as Research Assistants. Some students spend 1-2 years at Oak Ridge or Argonne doing their thesis research. All students have opportunities to interact with scientists from all over the world, and to travel to speak at international conferences, and to conferences of the American Physical Society. Research and travel are supported by a grant from the U.S. Department of Energy and by Vanderbilt University. Members of this group host international conferences periodically.

There is a strong theoretical group at Vanderbilt and, as well, the group supports short term visits (1-3 months) by leading theoretical scientists from the U.S. and abroad to work in the group. Over 60 Ph.D.'s have been awarded in experimental nuclear physics by our group and over 950 papers published in leading journals and research books.

The twelfth International Conference organized and hosted by the group was held in Sanibel, FL, in November, 2007, the forth International Conference on Fission and Properties of Neutron-rich Nuclei. The fifth conference in this series will be held in 2012.

The Vanderbilt nuclear structure group is the organizer of the Joint Institute for Heavy Ion Research at the HRIBF facility in Oak Ridge. This is a joint venture of Vanderbilt, the University of Tennessee/Knoxville, Oak Ridge National Laboratory, and the State of Tennessee. The Joint Institute buildings ($1,500,000 total costs) provide living accommodations and offices for outside users and a conference center with a new wing for a theory center. The Institute brings over 50 distinguished scientists each year to Tennessee from all over the world to work in research with our students and faculty. One member of our group (JHH) is the Director of the Joint Institute.

Some recent publications include:

1. "α Decay of 109I and Its Implications for the Proton Decay of 105Sb and the Astrophysical Rapid Proton-Capture Process," C. Mazzocchi, R. Grzywacz, S.N. Liddick, K.P. Rykaczewski, H. Schatz, J.C. Batchelder, C.R. Bingham, C.J. Gross, J.H. Hamilton, J.K. Hwang, S. Ilyushkin, A. Korgul, W. Krolas, K. Li, R.D. Page, D. Simpson, and J.A.Winger, Phys. Rev. Lett. 98, 212501 (5 pages) (2007).

2. "Shell Structure Beyond the Proton Drip Line Studied Via Proton Emission From Deformed 141Ho," M. Karny, K.P. Rykaczewski, R.K. Grzywacz, J.C. Batchelder, C.R. Bingham, C. Goodin, C.J. Gross, J.H. Hamilton, A. Korgul, W. Krolas, S.N. Liddick, K. Li, K.H. Maier, C. Mazzocchi, A. Piechaczek, K. Rykaczewski, D. Shapira, D. Simpson, M.N. Tantawy, J.A. Winger, C.H. Yu, E.F. Zganjar, N. Nikolov, J. Dobaczewski, A.T. Kruppa, W. Nazarewicz, and M.V. Stoitsov, Phys. Lett. B 664, 52-56 (2008).

3. Editors, J.H. Hamilton, A. V. Ramayya and H. K. Carter, Fourth International Conference on Fission and Properties of Neutron-Rich Nuclei, Singapore: World Scientific, 730 pages (2008).

4. "g-Factors, Spin-Parity Assignments, and Multipole Mixing Ratios of Excited States in N=82 Isotones 134Te, 135I," C. Goodin, N.J. Stone, A.V. Ramayya, A.V. Daniel, J.R. Stone, J.H. Hamilton, K. Li, J.K. Hwang, Y.X. Luo, J.O. Rasmussen, A. Gargano, A. Covello, and G.M. Ter-Akopian, Phys. Rev. C78, 044331 (6 pages) (2008).

5. "Identification of New Collective Bands in Neutron-Rich 102Zr," K. Li, J.H. Hamilton, A.V. Ramayya, S.J. Zhu, Y. X. Luo, J.K. Hwang, C. Goodin, J.O. Rasmussen, G.M. Ter-Akopian, A.V. Daniel, I.Y. Lee, S.C. Wu, R. Donangelo, J.D. Cole, W.C. Ma, and M.A. Stoyer, Phys. Rev. C78, 044317 (6 pages) (2008).

6. "Evolution of Chirality from γ Soft 108Ru to Triaxial 110,112Ru," Y. X. Luo, S. J. Zhu, J. H. Hamilton, J. O. Rasmussen, A. V. Ramayya, C. Goodin, K. Li, J. K. Hwang, X. L. Che, Z. Jang, S. Frauendorf, V. Dimitrov, Jing Ye Zhang, I. Stefanescu, A. Gelberg, G. M. Ter-Akopian, A. V. Daniel, M. A. Stoyer, R. Donangelo, J. D. Cole, N. J. Stone, Phys. Lett. B670, 307-312 (2009).

7. "Large β-Delayed Neutron Emission Probabilities in the 78Ni Region," J.A.Winger, S.V. Ilyushkin, K.P. Rykaczewski, C.J. Gross, J.C. Batchelder, C. Goodin, R. Grzywacz J.H. Hamilton, A. Korgul, W. Krolas, S.N. Liddick, C. Mazzocchi, S. Padgett, A. Piechaczek, M.M. Rajabali, D. Shapira, E.F. Zganjar, I.N. Borzov, Phys. Rev. Lett, 102, 142502 (4 pages) 2009.

8. "Identification of One-Phonon and Two-Phonon γ-Vibrational Bands in Odd-Z 103Nb Nucleus," J.G. Wang, S.J. Zhu, J.H. Hamilton, A.V. Ramayya, J.K. Hwang, S.H. Liu, K. Li, Y.X. Luo, J.O. Rasmussen, I.Y. Lee, H.B. Ding, Q. Xu, L. Gu, E.Y. Yeoh, Z.G. Xiao, W.C. Ma, Phys. Lett B675, 420-425 (2009).

9. "The First Observations of a Deformed Kπ Ground-State Band in 100Nb and the High-Spin Level Scheme of its 4n Fission Partner 148La," Y.X. Luo, J.O. Rasmussen, J.H. Hamilton, A.V. Ramayya, C. Goodin, S.J. Zhu, J.K. Hwang, K. Li, D. Fong, I. Stefanescu, I.Y. Lee, G.M. Ter-Akopian, A.V. Daniel, M.A. Stoyer, R. Donangelo, W.C. Ma and J.D. Cole, Nuclear Physics A825, 1-15 (2009).

10. "High-Spin States in 91,92,93Rb and 155,156Pm," J.K. Hwang, A.V. Ramayya, J.H. Hamilton, S.H. Liu, K. Li, H.L. Crowell, C. Goodin, Y.X. Luo, J.O. Rasmussen, and S.J. Zhu, Phys. Rev C (2009) in press.

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