Bulletin of the American Physical Society
2005 2nd Joint Meeting of the Nuclear Physics Divisions of the APS and The Physical Society of Japan
Sunday–Thursday, September 18–22, 2005; Maui, Hawaii
Session 2WE: Workshop 5B: Nuclear States Under Extreme Conditions of Binding and Isospin Aymmetry |
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Sponsoring Units: DNP JPS Chair: Tohru Motobayashi, RIKEN Room: Ritz-Carlton Hotel Amphitheatre |
Sunday, September 18, 2005 2:00PM - 2:30PM |
2WE.00001: Newly synthesized an isotope of the 113th element Invited Speaker: The convincing candidate event of the isotope of the 113th element, were observed, for the first time, in the $^{209}$Bi + $^{70}$Zn reaction at a beam energy of 349.0 MeV with a total dose of 1.7 $\times$ 10$^{19}$. Alpha decay energies and decay times of the candidates, $^{278}$113, $^{274}$111, and $^{270}$Mt, were (11.68 $\pm$ 0.04 MeV, 0.344 ms), (11.15 $\pm$ 0.07 MeV, 9.26 ms), and (10.03 $\pm$ 0.07 MeV, 7.16 ms), respectively. The production cross section of the isotope was deduced to be 55$^{+150}_{-45}$ fb (10$^{-39}$ cm$^{2})$ [1]. The experiment was performed at RIKEN (The Institute of Physical and Chemical Research) Linear Accelerator (RILAC) Facility. The evaporation residues produced by the fusion reaction with a $^{70}$Zn beam provided by the RILAC and the bismuth targets, were separated by a gas-filled recoil separator (GARIS) from the beam particles and the target recoils, and were collected at the focus of GARIS. We observed an event of implantation of an evaporation residue in the position-sensitive semiconductor detector followed by four consecutive alpha decays terminated by a spontaneous fission decay. Assignment of the event was based on genetic correlation of sequential alpha decays to the already known nuclides $^{266}$Bh and $^{262}$Db. The fourth alpha decay and the following spontaneous fission decay were assigned to be the decays of $^{266}$Bh and $^{262}$Db, respectively because of agreements of decay energies and decay times with the reported values [2]. As a consequence, the preceding three alpha decays were assigned to be ones of $^{278}$113, $^{274}$111, and $^{270}$Mt. \newline \newline [1] K. Morita, K. Morimoto, D. Kaji, T. Akiyama et al., J. Phys. Soc. Jpn. 73 (2004) 2593. \newline [2] P. A. Wilk et al., Phys. Rev. Lett. 85 (2000) 2697. [Preview Abstract] |
Sunday, September 18, 2005 2:30PM - 3:00PM |
2WE.00002: Fusion mechanism of weakly-bound nuclei Invited Speaker: Fusion mechanism of nuclei with halo structure is investigated theoretically. We describe the reaction as a three-body problem consisting of a halo nucleon and a core nucleus, which constitute the projectile, and a target nucleus. The three-body dynamics is solved by using the time-dependent wave-packet method. There are several advantages to employ the time-dependent method for the static problem: The method is useful to solve the three-body Schroedinger equation accurately. No explicit boundary condition is necessary to calculate the fusion probabilities from a wave-packet solution. A single wave- packet calculation provides reaction information for a certain incident energy range. The animation of the wave-packet dynamics provides us with intuitive pictures about the reaction dynamics. We find that the fusion probability of neutron halo nuclei is slightly hindered by the presence of the halo neutron, in opposite to a naive expectation that the weakly-bound neutron may enhance the fusion. In contrast, the fusion probability of proton halo nuclei is found to be much enhanced. The fusion cross sections are calculated for $^6$He - $^{238}$U and $^{11}$Be - $^{209}$Bi reactions, and are compared with recent measurements. [Preview Abstract] |
Sunday, September 18, 2005 3:00PM - 3:30PM |
2WE.00003: Innovations and Opportunities for laser spectroscopy of exotic nuclei in Europe Invited Speaker: High resolution laser spectroscopy is a well-established method for measuring nuclear moments and charge radii of radioactive nuclei. Recent breakthroughs in ion beam bunching with RFQ devices and the in-source application of resonance ionization spectroscopy (RIS) open up the prospect of measuring exotic nuclei. The first ion beam cooler-buncher to be used in this way was installed at the IGISOL facility in the Accelerator Laboratory, Jyvaskya (JYFL). The Birmingham-Manchester-JYFL collaboration has used the improved sensitivity to make measurements of the neutron-rich fission fragments in the zirconium and yttrium isotope chains. The fast release times of the IGISOL ion source has also allowed a number of isomers to be measured both in the yttrium chain and also amongst the recently-measured scandium isotopes. The beam time-structure has allowed the collaboration to demonstrate a collinear-beams resonance ionization spectroscopy technique (CRIS) which has no duty-cycle losses associated with low repetition rate lasers and has the potential of an order of magnitude increase in sensitivity. It has the additional advantage over in-source RIS measurements pursued by the RILIS and FURIOS groups of having much reduced Doppler broadening. A similar cooler-buncher is being built at Europe's premier on- line isotope separator facility, ISOLDE, at CERN. The first on-line experiments are planned for 2006. The benefit this will bring to the laser techniques, coupled with the higher production rates of the volatile exotic nuclei will allow measurements in hitherto unexplored regions of the nuclear landscape. In the longer term, plans are well developed for laser spectroscopy experiments at the future GSI-FAIR facility. The LaSpec collaboration involves more than ten groups from Europe and America who will apply a range of techniques at the facility's low energy beamline. [Preview Abstract] |
Sunday, September 18, 2005 3:30PM - 4:00PM |
2WE.00004: Recent experiments of interaction and reaction cross sections and the related results Invited Speaker: Recent experiments of interaction ($\sigma _{I})$ and reaction ($\sigma _{R})$ cross sections will be reviewed. Measurements of $\sigma _{I}$ and $\sigma _{R}$ have been proved to be effective tools to reveal the halo or skin structure in proton-rich and neutron-rich nuclei [1]. Very recently, $\sigma _{I}$ for $^{72-80}$Kr on carbon targets have been measured at FRS in GSI with relativistic energies ($\sim $1 $A$ GeV). Since the charge radii for the nuclei are known by optical isotope-shift measurements, by our $\sigma _{I}$ measurements the proton skin thickness of the nuclei can be investigated. Some tentative results of the measurements will be presented. $\sigma _{R}$ at intermediate energies are quite indispensable to deduce the effective matter density distributions by their energy dependence. Recently, $\sigma _{R}$ have been extensively measured at RIPS in RIKEN by a new setup [2]. As a byproduct, longitudinal momentum distributions of fragments from a projectile can be measured at the same time [3]. In special, one and two nucleon(s) removal channels can be observed at the same time. Recently, by the setup, we performed experiments for $^{14-19}$C and some proton rich nuclei including $^{23}$Al, that is a potential proton halo candidate due to its small proton separation energy. Some results of the experiments will also be introduced.\newline \newline [1] A.Ozawa et al., Nucl. Phys.A 693 (2001) 32.\newline [2] T.Zheng et al., Nucl. Phys. A 709 (2002) 103.\newline [3] T.Tamaguchi et al., Nucl. Phys. A 724 (2003) 3. [Preview Abstract] |
Sunday, September 18, 2005 4:00PM - 4:30PM |
2WE.00005: Pinpointing Structure of Exotic Nuclei Using Simple Signatures Invited Speaker: The advent of radioactive nuclear beams opens up entirely new regions of exotic nuclei for study. However, the experimental data on these nuclei will be sparse and different methods for elucidating structure from a few simple observables are necessary. An approach using the interacting boson approximation (IBA) model to interpret the low energy spectra of collective even-even nuclei will be presented. By investigating the intersection of constant contours of simple observables within the IBA symmetry triangle, the structure of a particular nucleus can be determined relative to the three dynamical symmetries of the IBA and to the phase structure in the triangle. This approach can be tested on isotopic chains near stability, then applied to exotic regions of nuclei. [Preview Abstract] |
Sunday, September 18, 2005 4:30PM - 5:00PM |
2WE.00006: Shell model applications to new regions of nuclei Invited Speaker: I will outline the progess that is being made on applying the techniques of large-basis configuration mixing to new region of nuclei, in particular the regions where radioactive beam facilities can explore now and over the next five years. The regions include those around the nuclei $^{24}$O, $^{42}$Si, $^{54}$Ca, $^{78}$Ni and $^{132}$Sn. The problems for determining the single-particle energies and the effective interactions starting from the NN interaction will be discussed. [Preview Abstract] |
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