Bulletin of the American Physical Society
3rd Joint Meeting of the APS Division of Nuclear Physics and the Physical Society of Japan
Volume 54, Number 10
Tuesday–Saturday, October 13–17, 2009; Waikoloa, Hawaii
Session 2WA: Workshop on Nuclear Physics with New-Generation Fast Rare Isotope Beams |
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Chair: Takashi Nakamura, Tokyo Institute of Technology Room: Kohala 1 |
Tuesday, October 13, 2009 2:00PM - 2:30PM |
2WA.00001: Radium-225: The Path to a Next Generation EDM Measurement Invited Speaker: Permanent electric dipole moments (EDMs) in atoms or molecules are signatures of time (T)- and parity (P)-violation. Experimental searches for these EDMs represent an excellent window to physics beyond the standard model. In the nuclear sector, the best limits for EDMs are currently set by measurements on the neutron and the diamagnetic atom $^{199}$Hg. A promising avenue for extending these searches is to take advantage of the large enhancement in the atomic EDM predicted for heavy octupole-deformed nuclei, as can be found in the radium and radon isotopic chains. One of these favorable case is $^{225}$Ra, which is calculated to be two to three orders of magnitude more sensitive to T-violating interactions than $^{199}$Hg. We are developing a next generation EDM search around laser-cooled and trapped $^{225}$Ra, which involves measuring the nuclear spin precession of polarized $^{225}$Ra atoms confined in an optical dipole trap. I will report on our recent experimental progress and on the impact of next generation isotope facilities on this line of research. [Preview Abstract] |
Tuesday, October 13, 2009 2:30PM - 3:00PM |
2WA.00002: Study of Exotic Nuclear Structures via Total Reaction Cross Sections Invited Speaker: Nuclear radius is one of the most basic physical quantities to study unknown exotic nuclei. A number of radii for unstable nuclei were studied through measurements of interaction cross sections (${{\sigma}\mathrm{_{I}}}$) at high energies, using the Glauber-type calculation (Optical-Limit approximation (OLA) of Glauber theory) to investigate halo and skin structures of exotic nuclei. On the other hand, it was indicated that reaction cross sections (${{\sigma}\mathrm{_{R}}}$) at intermediate energies (from several tens to hundreds of MeV/nucleon) were more sensitive to dilute nucleon density distribution owing to large nucleon-nucleon total cross sections (${{\sigma}\mathrm{_{NN}}}$) compared to high-energy region. Recently, we developed a new method to deduce nucleon density distributions from the energy dependences of ${{\sigma} \mathrm{_{R}}}$, through the precise measurements of ${{\sigma} \mathrm{_{R}}}$ for various nuclei and some modifications of Glauber-type calculation. Using this method, we studied nucleon density distributions of light nuclei by measuring ${{\sigma} \mathrm{_{R}}}$ for those nuclei at HIMAC (Heavy ion Medical Accelerator in CHIBA), NIRS (National Institute of Radiological Sciences). And very recently, we deduced nuclear radii of neutron-rich Ne isotopes (${^{28-32}}$Ne) which are in the island-of-inversion region by measuring ${{\sigma}\mathrm{_{I}}} $ using BigRIPS at RIBF (RI Beam Factory) to study nuclear structures of those isotopes using our method. In this workshop, results of nucleon density distributions obtained at HIMAC and results of the studies of Ne isotopes at RIBF will be introduced and discussed. [Preview Abstract] |
Tuesday, October 13, 2009 3:00PM - 3:30PM |
2WA.00003: Extracting spectroscopic factors from direct reactions Invited Speaker: Direct reactions have been used to probe the structure of the nucleus for decades. After some decline in the 80's and 90's these methods have more recently had a surge in popularity, and new techniques have been added to the experimentalists toolbox. One goal of direct reaction experiments is to extract spectroscopic factors (SFs), related to the shell occupancy. SFs extracted from neutron knockout reactions show reductions, compared to the theoretical value, that are related to the neutron separation energy [1], whereas SFs from the well-established (e,e'p) reaction on stable nuclei are consistently 50{\%} - 60{\%} lower than those expected from the independent-particle shell model [2] over a wide range of masses. $\backslash $pardAs the extraction of spectroscopic factors from direct reaction measurements requires the comparison of data with calculated differential cross sections, the results are by nature model dependent. The influence of different scattering (commonly optical), and bound state potentials, should not be over-looked. Recent attempts to reanalyze single-neutron transfer data using a consistent approach have shown agreement with large basis shell model calculations [3], clearly conflicting with both the (e,e'p) and the knockout data. It has been suggested that the Asymptotic Normalization Coefficient (ANC) is a more valid quantity to extract when the reaction is peripheral [4]. spectroscopic factors are, how they are extracted and what they really mean will be discussed in this talk.\\[4pt] [1] Alexandra Gade, and Thomas Glasmacher, Prog Part. Nucl. Phys. 60 (2008) 161-224.\\[0pt] [2] G.J. Kramer, H.P. Blok, and L. Lapik\'{a}s, Nucl. Phys. A679 (2001) 267-286.\\[0pt] [3] Jenny Lee, M.B. Tsang, and W.G. Lynch, Phys. Rev C 75, (2007), 064320.\\[0pt] [4] D.Y. Pan, F.M. Nunes, and A.M. Mukhamedzhanov, Phys. Rev. C 75, (2007) 024601. [Preview Abstract] |
Tuesday, October 13, 2009 3:30PM - 4:00PM |
2WA.00004: COFFEE BREAK
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Tuesday, October 13, 2009 4:00PM - 4:30PM |
2WA.00005: Alpha inelastic scattering and cluster structures in light stable and unstable nuclei Invited Speaker: Alpha particle clustering where four nucleons strongly correlate to constitute an alpha cluster is an important concept in nuclear physics. The alpha cluster behaves as a subunit of the atomic nucleus and exhibits characteristic phenomena which cannot be described by single-particle models like the shell model. Since the theoretical description of the clustering phenomena under the shell-model framework requires a huge number of single-particle bases, it is generally difficult to treat the clustering phenomena in the truncated shell-model space. It is widely known that the ground-state wave function by the SU (3) shell model is mathematically equivalent to that by the alpha cluster model. This means the alpha particles inherently exists even in the compact ground-state wave function although its alpha cluster structure is not fully developed. Thus, the spatially developed alpha-cluster states are expected to be excited by stimulating the relative motion between the alpha particles in the ground state. We recently proposed that the inelastic alpha scattering is a very useful probe to examine the alpha cluster structure. Since the alpha inelastic scattering selectively excites isoscalar natural-parity transitions, it is very suitable to excite the inter-cluster relative motion. We measured the cross sections for the alpha inelastic scattering from $^{11}$B, $^{12}$C, $^{13}$C, and $^{24}$Mg. The experiment was carried out by using a 400-MeV alpha beam at Research Center for Nuclear Physics, Osaka University. The experimental results were compared with the shell-model and cluster-model calculations, and the alpha-cluster structures in those nuclei were discussed. The present approach by means of the alpha inelastic scattering is very useful to examine the alpha-cluster structures in stable nuclei, and it should be naturally applied to unstable nuclei. In the present talk, the experimental details and results on the stable nuclei will be reported. Future prospects on the extended studies in unstable nuclei will be also discussed. [Preview Abstract] |
Tuesday, October 13, 2009 4:30PM - 5:00PM |
2WA.00006: Pursuing the most neutron-rich nuclei, status and prospectives Invited Speaker: The production of the most neutron-rich nuclei by the fragmentation of $^{48}$Ca and $^{76}$Ge beams at Michigan State will be presented. The cross sections were measured for a large range of nuclei including fifteen new isotopes that are the most neutron-rich nuclides of magnesium, aluminum, silicon, and the elements from chlorine to manganese. The observation of $^{42}$Al was itself surprising. The cross sections of several new nuclei were found to be enhanced relative to a simple thermal evaporation framework, previously shown to describe similar production cross sections. This may be an indication that precursor excited nuclei in the region around $^{62}$Ti that decay to the observed nuclei are more stable than predicted by current mass models and may be evidence for a new island of inversion similar to that centered on $^{31}$Na. The next generation radioactive beam facility, FRIB, for the United States will be constructed at Michigan State University. A brief overview of the proposed facility and the prospective for future studies of the most neutron-rich nuclei will be presented. [Preview Abstract] |
Tuesday, October 13, 2009 5:00PM - 5:30PM |
2WA.00007: In-beam $\gamma$-ray spectroscopy at the RIBF: recent results and future prospects Invited Speaker: With the commissioning of the BigRIPS projectile fragment separator and the ZeroDegree spectrometer at the Radioactive Ion Beam Factory (RIBF) at the RIKEN Nishina Center a new window to study nuclei far from stability has been opened. Various experimental methods can now be applied to exploit the intense and high-energy primary and secondary beams at the RIBF. In a first set of experiments in-beam $\gamma$-ray spectroscopy has proved to be a very promising tool to study exotic nuclei far from stability. The so-called DayOne experimental campaign was carried out at the RIBF in November and December 2008, which comprises a set of experiments using the same primary beam $^{48}$Ca at 345 MeV/$u$ and similar, or at least non-interfering, experimental setups. During this campaign the first spectroscopic study of the N=22 nucleus $^{32}$Ne was carried out. A single $\gamma$-ray transition with an energy of 722(9) keV was observed in both inelastic scattering of a 226 MeV/$u$ $^{32}$Ne beam on a Carbon target and proton removal from $^{33}$Na at 245 MeV/$u$, which is assigned to the de-excitation of the first $J^\pi$ = $2^+$ state in ${32}$Ne to the $0^+$ ground state. The low excitation energy and a comparison to state of the art shell model calculations demonstrate that the Island of Inversion extends to at least N=22 for the Ne isotopes. I will give a short overview of the existing facilities and then focus on the first experimental campaign carried out with BigRIPS and ZeroDegree. The experimental setup used for in-beam $\gamma$-ray spectroscopy will be introduced followed by a presentation of first results. An outlook will be given. [Preview Abstract] |
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