Bulletin of the American Physical Society
2005 APS April Meeting
Saturday–Tuesday, April 16–19, 2005; Tampa, FL
Session C12: Nuclear Reactions and Rare Isotope Beams |
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Sponsoring Units: DNP Chair: G. Souliotis, Texas A&M University Room: Marriott Tampa Waterside Room 11 |
Saturday, April 16, 2005 1:30PM - 1:42PM |
C12.00001: Ab Initio Study of the Level Ordering Anomaly in $^{11}$Be Christian Forssen, Petr Navratil, W. Erich Ormand, Etienne Caurier We are presenting the first \emph{ab initio} structure investigation of the loosely bound $^{11}$Be nucleus, together with a study of the surrounding, stable isotopes $^{9}$Be, $^{11}$B and $^{13}$C. The nuclear structure of these isotopes is particularly interesting due to the appearance of a parity-inverted ground state in $^{11}$Be. Our study is performed in the framework of the \emph{ab initio} no-core shell model (NCSM). Results obtained using four different, high-precision two-nucleon interactions, in model spaces up to $9\hbar\Omega$ (with matrix dimensions exceeding $1.1 \times 10^9$), are shown. We present results on binding energies, excitation spectra, radii, and electromagnetic observables. Furthermore, the recently developed ability to extract cluster form factors from NCSM wave functions is utilized, and the overlap of the $^{11}$Be ground state with different $^{10}$Be$ + n$ channels is studied. Support from the LDRD contract No. 04-ERD-058, and from U.S. Department of Energy, Office of Science, (Work Proposal Number SCW0498) is acknowledged. [Preview Abstract] |
Saturday, April 16, 2005 1:42PM - 1:54PM |
C12.00002: The Level Structure of Neutron Rich $^{26}$Na S. Lee, S.L. Tabor, C.R. Hoffman, D.B. Campbell, J. Pavan, K.W. Kemper, M.A. Riley, M. Wiedeking, A. Pipidis, M.W. Cooper, C. Chandler T=2 $^{26}$Na was populated from the $^{14}$C($^{14}$C,d) reaction at 22MeV at Florida State University. Charged particles were detected in a particle detector telescope consisting of three segmented silicon detectors.$\gamma$rays were measured using an array of Compton-suppressed HPGe detectors. The array consisted of three 2-fold segmented ``clover'' detectors and seven single Ge detectors. The data was analyzed from the d-$\gamma$ and d-$\gamma$-$\gamma$ coincidences with Gnuscope a software package for particle-gamma analysis. Several new excited states and new $\gamma$-ray transitions were found. Angular distributions were measured to assign spins and parities to the new levels. The new results were compared with USD shell model calculations and previous measurements. \newline \newline This work was supported in part by the U.S. National Science Foundation. [Preview Abstract] |
Saturday, April 16, 2005 1:54PM - 2:06PM |
C12.00003: Survey of ground state neutron spectroscopic factors from Li to Cr isotopes Hui-Ching Lee, Betty Tsang, William Lynch The success of the Shell Model has prompted many measurements to extract the spectroscopic factors which describe the configuration of single particle orbitals. We have extracted the ground state to ground state neutron spectroscopic factors for 79 nuclei ranging in Z from 3 to 24 by analyzing the past measurements of the angular distributions of (d,p) and (p,d) reactions in a systematic and consistent manner [1]. For the Ca isotopes from $^{40}$Ca to $^{48}$Ca, the spectroscopic factors follow the predictions of the single particle model predictions as well as predictions from shell model suggesting Ca isotopes have good spherical cores with well defined valence nucleons. For the 59 nuclei where modern shell model calculations [Oxbash] are available, with the exception of the deformed F and Ne isotopes, the experimental spectroscopic factors for most nuclei agree with predictions from modern day shell model to within 20{\%}. This work is supported by the NSF Grant No. NSF-PHY-01-10253 and SURE. Reference: [1] X.D.Liu, M.A.Famiano,W.G.Lynch,M.B.Tsang,and J.A.Tostevin, Phys. Rev. C69 (2004) 1. [Preview Abstract] |
Saturday, April 16, 2005 2:06PM - 2:18PM |
C12.00004: Two-neutron knockout reaction to final levels in the $T_{\rm z}$~=~-2 nuclei $^{24}$Si, $^{28}$S, and $^{32}$Ar K. Yoneda, P.G. Hansen, D. Bazin, B.A. Brown, C.M. Campbell, J.M. Cook, D.C. Dinca, A. Gade, T. Glasmacher, T.E. Hoagland, J.L. Lecouey, W.F. Mueller, H. Olliver, B.M. Sherrill, J.R. Terry, P.D. Cottle, K.W. Kemper, R. Reynolds, B.T. Roeder, J.A. Tostevin Two-proton knockout from a neutron-rich nucleus has recently been shown$^1$ to proceed as a direct reaction. While the inclusive and partial cross sections could be understood in a simple theory, a more precise description can be based on a scheme that combines the full shell-model two-nucleon spectroscopic amplitudes with eikonal reaction theory$^2$. We report here a first attempt to investigate the analogous two-neutron knockout from a proton-rich nucleus at energies around 100~MeV/nucleon. The projectiles $^{26}$Si, $^{30}$S, and $^{34}$Ar lead to products that have a 2$^+$ level as the only bound excited state, and are thus well suited for an accurate test of the theory. The experiment carried out at the NSCL observed this gamma peak in coincidence with the projectile residues in all three cases. The partial cross sections to the $0$^+$ and 2$^+$ levels will be discussed and compared with theory. This work was supported by NSF grants PHY-0110253, PHY-9875122, PHY-0244453, and PHY-0342281.\\ 1. D.~Bazin et al., Phys. Rev. Lett. 41 (2003) 012501.\\ 2. J.~A.~Tostevin et al., Phys. Rev. C 70, 064602 (2004). [Preview Abstract] |
Saturday, April 16, 2005 2:18PM - 2:30PM |
C12.00005: Direct quantitative observation of a negative-parity intruder state in $^{28}$Ne P.G. Hansen, J.R. Terry, D. Bazin, B.A. Brown, C.M. Campbell, J.A. Church, J.M. Cook, A.D. Davies, D.C. Dinca, J. Enders, A. Gade, T. Glasmacher, J.L. Lecouey, W.F. Mueller, H. Olliver, B.M. Sherrill, K. Yoneda, J.A. Tostevin We present results for the neutron knockout from a 70 MeV beam of $^{28}$Ne interacting with a $^9$Be target. The projectile residues were detected in the high-resolution S-800 spectrograph and excited levels were identified via gamma-ray coincidences observed with the array of segmented germanium detectors SeGA. Events not coincident with gamma rays amounted to 38\%. These were predominantly associated with a momentum distribution with a clear $l$=3 shape corresponding to a spectroscopic factor of close to unity, so that, on the average, at least one of the 18 neutrons in the projectile must be in an $f_{7/2}$ orbital. This confirms for the first time the strong presence of $f$-shell intruders in the ground state predicted for this nucleus in the Monte-Carlo shell-model calculations by Utsuno et al., Phys. Rev. C 60, 054315 (1999). [Preview Abstract] |
Saturday, April 16, 2005 2:30PM - 2:42PM |
C12.00006: Determination of l-values for States in $^{39}$S and $^{41}$S via One-Neutron Knockout Reactions$^{*}$ B.T. Roeder, K.W. Kemper, V. Tripathi, D. Bazin, M. Bowen, C.M. Campbell, J.M. Cook, D.C. Dinca, A. Gade, T. Glasmacher, P.G. Hansen, W.F. Mueller, H. Olliver, J.R. Terry, K. Yonedo, N. Aoi, T. Motobayashi, S. Takeuchi, H. Iwasaki, H. Sakurai, H. Suzuki, S. Kanno, T. Nakamura One-nucleon knockout reactions have been used extensively to study exotic nuclei in inverse kinematics at intermediate energies. In this work, momentum distributions for $^{47}$Ca, $^{47}$K, $^{39}$S, and $^{41}$S were obtained by using $^{48}$Ca, $^{40}$S and $^{42}$S beams at 100 MeV/nuc to bombard a liquid deuterium target. $\gamma$-decays from the reaction products were detected in-flight by the SeGA array and the particles were detected by the S800 mass spectrometer at NSCL. Coincidences between the particles and the gamma rays are used to identify specific reaction products and to reconstruct momentum distributions for specific states. The resulting momentum distributions observed form these experiments will be compared to calculations in order to identify the angular momentum l-value carried by the knocked-out nucleon. Values for "l" for states in $^{47}$Ca and $^{47}$K will be compared to previous work and proposed l-values for new states in $^{39}$S and $^{41}$S will be presented. $^{*}$Work supported by the U.S. National Science Foundation, the State of Florida, and the Japan Society for the Promotion of Science. [Preview Abstract] |
Saturday, April 16, 2005 2:42PM - 2:54PM |
C12.00007: Evolution of collectivity approaching N=28 for silicon and sulfur isotopes C.M. Campbell, D. Bazin, M.D. Bowen, B.A. Brown, J.M. Cook, D.-C. Dinca, A. Gade, T. Glasmacher, W.F. Mueller, H. Olliver, K. Starosta, J.R. Terry, K. Yoneda, N. Aoi, H. Sakurai, S. Kanno, T. Motobayashi, S. Takeuchi, S.P. Weppner Excited states in neutron-rich silicon and sulfur nuclei have been studied at NSCL using inverse kinematics inelastic proton scattering. Exotic cocktail beams impinged upon a RIKEN liquid hydrogen target placed at the target position of the S800 spectrograph. Gamma-rays collected by SeGA (Segmented Germanium Array) were used to tag scattering events that excited specific states in each nucleus, and the S800 spectrograph provided event-by-event isotopic and reaction channel identification. Analysis of (p,p') excitation cross-sections provided information on nuclear deformation, while analysis of the gamma-ray spectra has identified new levels in these neutron-rich nuclei. The evolution of collectivity with increasing neutron number will be discussed. [Preview Abstract] |
Saturday, April 16, 2005 2:54PM - 3:06PM |
C12.00008: Techniques for (d,p$\gamma$) Measurements at the HRIBF M.S. Johnson, A. Kronenberg, D.W. Bardayan, J.C. Blackmon, C.D. Nesaraja, M.S. Smith, J.A. Cizewski, K.L. Jones, S.D. Pain, J.S. Thomas, J.A. Howard, R.L. Kozub, D.W. Visser Neutron transfer measurements on exotic nuclei are important for astrophysics and nuclear structure. Such reactions provide information such as excitation energy, angular momentum and spectroscopic strength for neutron single-particle states. Using inverse kinematics for (d,p) reactions enables measurements to be made on neutron-rich nuclei which are too short-lived to make into targets. Studies of neutron-rich nuclei are important for understanding the astrophysical $r$-process path. We are developing techniques to include $\gamma$-ray measurements in coincidence with proton detection. This approach offers many benefits over standard (d,p) reaction. Techniques for (d,p$\gamma$) reactions in inverse kinematics will be presented. [Preview Abstract] |
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