A new free weekly publication from APS

Physics - A new free weekly publication from APS
Please visit physics.aps.org
 

SELECTED ARTICLES (0)

Physical Review C

(Nuclear Physics)

July 2006

Volume 74, Number 1 , Articles (01xxxx)

Click on icons for further information Rapid Communication icon   Physics Viewpoint icon   Focus icon   Free to Read icon

Rapid Communication icon  Rapid Communication
     Close

     Close
Physics Viewpoint icon  Physics Viewpoint
Selected for a Viewpoint in Physics. Please visit http://physics.aps.org/.
     Close
Focus icon  Featured in Phys. Rev. Focus
Please visit http://focus.aps.org.
     Close
Free to Read icon  Free to Read
Marks articles whose full text is available without a subscription. See the FREE TO READ FAQ.
     Close

RAPID COMMUNICATIONS
Rapid

Global properties of the Skyrme-force-induced nuclear symmetry energy
Wojciech Satula, Ramon A. Wyss, and Michal Rafalski
Published 10 July 2006 (5 pages)
011301(R)  Full Text: PDF (192 kB)  | Buy Article
+
Show Abstract
A novel concept for the nuclear symmetry energy (NSE) is corroborated by large scale calculations. The paper firmly demonstrates that within the local density approximation, the value of the NSE coefficient, asym(A), depends on two basic ingredients: the mean-level spacing, epsilon(A), and the effective strength of the isovector mean-potential, kappa(A). Surprisingly, our results reveal that these two basic ingredients of asym are almost equal after rescaling them linearly by the isoscalar and the isovector effective masses, respectively. This result points towards a hidden and hitherto unresolved fundamental property of the effective nuclear interaction. In addition, our analysis yields naturally the ratio of the surface-to-volume contributions to asym with a value of ~1.6, consistent with hydrodynamical estimates for the static dipole polarizability as well as the neutron-skin. Although the present study is restricted to energy density functionals obtained from Skyrme forces the method is general and can easily be applied to more general local energy density functionals and nonnuclear bifermionic systems.
Rapid

Calculating the nuclear mass in the very high angular momentum regime
B. G. Carlsson and I. Ragnarsson
Published 27 July 2006 (5 pages)
011302(R)  Full Text: PDF (175 kB)  | Buy Article
+
Show Abstract
Macroscopic-microscopic methods are applied in the high-spin regime to calculate the nuclear binding energy ("mass") as a function of proton number, neutron number, and angular momentum. Masses at high spin are calculated using the cranked Nilsson-Strutinsky model together with two different liquid drop models, the Lublin-Strasbourg drop model and the finite range liquid drop model. When comparisons are made with experimental data, a similar agreement between theory and experiment is obtained as for ground-state masses.
Rapid

Forward-backward multiplicity correlations in sqrt(s[sub NN])=200 GeV Au+Au collisions
B. B. Back et al. (PHOBOS Collaboration)
Published 13 July 2006 (5 pages)
011901(R)  Full Text: PDF (130 kB)  | Buy Article
+
Show Abstract
Forward-backward correlations of charged-particle multiplicities in symmetric bins in pseudorapidity are studied to gain insight into the underlying correlation structure of particle production in Au+Au collisions. The PHOBOS detector is used to measure integrated multiplicities in bins centered at eta, defined within |eta|<3, and covering intervals Deltaeta. The variance sigmaC<sup>2</sup> of a suitably defined forward-backward asymmetry variable C is calculated as a function of eta,Deltaeta, and centrality. It is found to be sensitive to short-range correlations, and the concept of "clustering" is used to interpret comparisons to phenomenological models.
Rapid

First experimental constraints on the interference of (3/2)+ resonances in the 18F(p,alpha)15O reaction
K. Y. Chae, D. W. Bardayan, J. C. Blackmon, D. Gregory, M. W. Guidry, M. S. Johnson, R. L. Kozub, R. J. Livesay, Z. Ma, C. D. Nesaraja, S. D. Pain, S. Paulauskas, M. Porter-Peden, J. F. Shriner Jr., N. Smith, M. S. Smith, and J. S. Thomas
Published 10 July 2006 (5 pages)
012801(R)  Full Text: PDF (308 kB)  | Buy Article
+
Show Abstract
The interference effects among Jpi=3/2+ resonances in the 18F+p system have not been previously measured. R-matrix calculations show that the cross sections above the Ec.m.=665 keV resonance are sensitive to the interference between the Ec.m.=8, 38, and 665 keV resonances. An excitation function for the 1H(18F,alpha)15O reaction has been measured in the energy range of Ec.m.=663-877 keV using radioactive 18F beams at the Holifield Radioactive Ion Beam Facility (HRIBF). By comparing the observed cross sections with the R-matrix calculations, we provide the first experimental constraints on the interference. Upper limits on proton widths (Gammap) of the Ec.m.=827 and 842 keV resonances have been set as well.

ARTICLES

Nucleon-Nucleon Interaction, Few-Body Systems

Neutron-neutron final-state interaction in the 2H(n,p)2n reaction at En=17.4 MeV
W. von Witsch, X. Ruan, and H. Witala
Published 10 July 2006 (5 pages)
014001  Full Text: PDF (261 kB)  | Buy Article
+
Show Abstract
The neutron-neutron (nn) final-state interaction has been investigated in the n+d-->p+2n reaction in kinematically incomplete geometry at En=17.4 MeV, detecting the protons emitted around zero degrees. Absolute cross-section data for the neutron-deuteron breakup reaction were obtained via (n,d) elastic scattering, which was measured simultaneously. The data were analyzed by means of detailed Monte Carlo simulations based on rigorous three-body calculations using CD-Bonn and two other high-quality potentials for the nucleon-nucleon interaction. The breakup spectrum is described very well on an absolute scale over the entire energy range investigated. The value of the nn scattering length deduced from the cross section in the FSI peak is ann=-16.5±0.9 fm, where the error indicates the combined statistical and systematic uncertainty.

Twice-iterated boson-exchange scattering amplitudes
N. Kaiser
Published 18 July 2006 (5 pages)
014002  Full Text: PDF (154 kB)  | Buy Article
+
Show Abstract
We calculate at two-loop order the complex-valued scattering amplitude related to the twice-iterated scalar-isovector boson exchange between nucleons. Compared to the once-iterated boson-exchange amplitude, it shows less dependence on the scattering angle. We calculate also the iteration of the (static) irreducible one-loop potential with the one-boson exchange and find similar features. Together with the irreducible three-boson exchange potentials and the two-boson exchange potentials with vertex corrections, which are also evaluated analytically, our results comprise all nonrelativistic contributions from scalar-isovector boson exchange at one- and two-loop orders. The applied methods can be straightforwardly adopted to the pseudoscalar pion with its spin- and momentum-dependent couplings to the nucleon.

Power counting with one-pion exchange
Michael C. Birse
Published 24 July 2006 (14 pages)
014003  Full Text: PDF (264 kB)  | Buy Article
+
Show Abstract
Techniques developed for handing inverse-power-law potentials in atomic physics are applied to the tensor one-pion exchange potential to determine the regions in which it can be treated perturbatively. In S,P, and D waves, the critical values of the relative momentum are less than or of the order of 400 MeV. The Wilsonian renormalization group (RG) is then used to determine the power counting for short-range interaction in the presence of this potential. In the P and D waves, where there are no low-energy bound or virtual states, these interactions have half-integer RG eigenvalues and are substantially promoted relative to naive expectations. These results are independent of whether the tensor force is attractive or repulsive. In the 3S1 channel, the leading term is relevant, but it is demoted by half an order compared to the counting for the effective-range expansion with only a short-range potential. The tensor force can be treated perturbatively in those F waves and above that do not couple to P or D waves. The corresponding power counting is the usual one given by naive dimensional analysis.

Incoherent pion photoproduction on the deuteron in the first resonance region
M. I. Levchuk, A. Yu. Loginov, A. A. Sidorov, V. N. Stibunov, and M. Schumacher
Published 31 July 2006 (20 pages)
014004  Full Text: PDF (1088 kB)  | Buy Article
+
Show Abstract
Incoherent pion photoproduction on the deuteron is studied in the first resonance region. The unpolarized cross section, the beam asymmetry, and the vector and tensor target asymmetries are calculated in the framework of a diagrammatic approach. Pole diagrams and one-loop diagrams with NN scattering in the final state are taken into account. An elementary operator for pion photoproduction on the nucleon is taken in various on-shell forms and calculated using the SAID and MAID multipole analyses. Model dependence of the obtained results is discussed in some detail. A comparison with predictions of other works is given. Although a reasonable description of many available experimental data on the unpolarized total and differential cross sections and photon asymmetry has been achieved, in some cases a significant disagreement between the theory and experiment has been found. Invoking known information on the reactions gammad-->pi0d and gammad-->np we predict the total photoabsorption cross section for deuterium. We find that our values strongly overestimate experimental data in the vicinity of the Delta peak.

Nuclear Structure

Fission modes of 256Fm and 258Fm in a microscopic approach
L. Bonneau
Published 5 July 2006 (12 pages)
014301  Full Text: PDF (264 kB)  | Buy Article
+
Show Abstract
A static microscopic study of potential-energy surfaces within the Skyrme-Hartree-Fock-plus-BCS model is carried out for the 256Fm and 258Fm isotopes with the goal of deducing some properties of spontaneous fission. The calculated fission modes are found to be in agreement with the experimentally observed asymmetric-to-symmetric transition in the fragment-mass distributions and with the high- and low-total-kinetic-energy modes experimentally observed in 258Fm. Most of the results are similar to those obtained in macroscopic-microscopic models as well as in recent Hartree-Fock-Bogolyubov calculations with the Gogny interaction, with a few differences in their interpretations. In particular an alternative explanation is proposed for the low-energy fission mode of 258Fm.

Yrast states and band crossings in the neutron-deficient platinum isotopes 169-173Pt
D. T. Joss, J. Simpson, D. E. Appelbe, C. J. Barton, D. D. Warner, K. Lagergren, B. Cederwall, B. Hadinia, S. Eeckhaudt, T. Grahn, P. T. Greenlees, P. M. Jones, R. Julin, S. Juutinen, H. Kettunen, M. Leino, A.-P. Leppänen, P. Nieminen, J. Pakarinen, J. Perkowski, P. Rahkila, C. Scholey, J. Uusitalo, K. Van de Vel, R. D. Page, E. S. Paul, D. R. Wiseman, and M. A. Riley
Published 6 July 2006 (10 pages)
014302  Full Text: PDF (264 kB)  | Buy Article
+
Show Abstract
The yrast states in the light platinum isotopes 169-173Pt have been investigated in a recoil-decay tagging experiment using the JUROGAM gamma-ray spectrometer in conjunction with the RITU gas-filled recoil separator and the GREAT tagging spectrometer. Gamma-ray transitions have been established for the first time in the odd-N isotopes, 169Pt and 173Pt, and the yrast sequences in 170Pt and 172Pt have been extended. We discuss the possibility that the weakly deformed yrast structures of 170Pt, 172Pt, and 173Pt are crossed by a deformed intruder configuration at spin ~8[h-bar].

Correlations and effective interactions in nuclear matter
P. Bozek, D. J. Dean, and H. Müther
Published 11 July 2006 (8 pages)
014303  Full Text: PDF (264 kB)  | Buy Article
+
Show Abstract
We performed self-consistent Green's function calculations for symmetric nuclear matter using realistic nucleon-nucleon (NN) interactions and effective low-momentum interactions (Vlow-k), which are derived from such realistic NN interactions. We compare the spectral distributions resulting from such calculations. We also introduce a density-dependent effective low-momentum interaction that accounts for the dispersive effects in the single-particle propagator in the medium.

Global calculation of alpha-decay half-lives with a deformed density-dependent cluster model
Chang Xu and Zhongzhou Ren
Published 11 July 2006 (10 pages)
014304  Full Text: PDF (264 kB)  | Buy Article
+
Show Abstract
A global calculation of favored alpha-decay half-lives of both even-A and odd-A deformed nuclei is carried out in the framework of a deformed version of the density-dependent cluster model (DDCM). The influence of nuclear deformation on alpha-decay half-lives is taken into account in the deformed DDCM. The microscopic potential between the spherical alpha particle and the deformed daughter nucleus is evaluated numerically from the double-folding model by the multipole expansion method. The deformation and orientation dependence of the alpha-core potential is analyzed and discussed. The formulas of the deformed DDCM are presented in detail, and a large number of numerical calculations of medium and heavy nuclei with available data are completed. The total number of alpha emitters calculated in this article is 485, and this covers the nuclei with Z=52-110. This is a complete study of alpha-decay half-lives on both even-A and odd-A nuclei with deformed microscopic potentials. The numerical results obtained by the deformed DDCM are in good agreement with the experimental data.

Competition between collective and noncollective excitation modes at high spin in 124Ba
A. Al-Khatib et al.
Published 11 July 2006 (18 pages)
014305  Full Text: PDF (264 kB)  | Buy Article
+
Show Abstract
High-spin states in 124Ba were investigated in two experiments using the 64Ni(64Ni, 4n)124Ba reaction at three different beam energies. In-beam gamma-ray coincidences were measured with the Euroball and Gammasphere detector arrays. In the experiment with Euroball, the CsI detector array Diamant was employed to discriminate against charged-particle channels. Six new rotational bands were observed in 124Ba, and previously known bands were extended to higher spins. One of the bands shows a transition from collective to noncollective behavior at high spins. Configuration assignments are suggested on the basis of comparison with cranked shell model and cranked Nilsson-Strutinsky calculations.

Classical chaos in the geometric collective model
Pavel Stránský, Matús Kurian, and Pavel Cejnar
Published 11 July 2006 (13 pages)
014306  Full Text: PDF (264 kB)  | Buy Article
+
Show Abstract
Collective vibrations and rotations of atomic nuclei are investigated from the classical viewpoint within the geometric collective model. It is shown that the model, even in its truncated form, exhibits a very sophisticated interplay of regular and chaotic modes of motions. We quantify the proportion of regular and chaotic orbits in the phase space and analyze its sensitive dependence on the model control parameters, energy, and angular momentum. A quasi-regular region is observed at low excitation energies in a bounded domain of the control parameter on the deformed side of the shape phase diagram, and another one at higher energies around the transition between spherical and deformed shapes. We also demonstrate a tendency for overall suppression or enhancement of chaos with angular momentum, depending on the values of control parameters.

Macroscopic pairing vibrational model, self-consistent pairing coupling constant, and the fifth term of von Weizsäcker's semiempirical formula
C. H. Dasso and M. I. Gallardo
Published 12 July 2006 (8 pages)
014307  Full Text: PDF (264 kB)  | Buy Article
+
Show Abstract
The implementation of a number-conserving formalism for pair-addition and pair-removal modes has impaired the possibility of developing an intuitive and self-consistent picture for collective pairing modes. In this paper, we show how a relaxation of this constraint leads to a unified model with true predictive power.

Triaxial shape induced by couplings between equatorial orbitals
Bao-Guo Dong, Hong-Chao Guo, and I. Ragnarsson
Published 13 July 2006 (6 pages)
014308  Full Text: PDF (264 kB)  | Buy Article
+
Show Abstract
The observed signature splitting at high spin in the odd-odd isotopes 126-132Pr and its description in cranking calculations suggest that 126Pr (Z=59,N=67) is triaxially deformed at intermediate values. The triaxial shape is explained as caused by specific couplings between the orbitals. These couplings are active for N=67 but not for N=69.

Excitation of dipole resonances in 4He and in the alpha clusters of 6Li and 7Li
T. Yamagata, N. Warashina, H. Akimune, S. Asaji, M. Fujiwara, M. B. Greenfield, H. Hashimoto, R. Hayami, T. Ishida, K. Kawase, M. Kinoshita, T. Kudoh, K. Nakanishi, S. Nakayama, S. Okumura, K. Sagara, M. Tanaka, H. Utsunomiya, and M. Yosoi
Published 14 July 2006 (7 pages)
014309  Full Text: PDF (264 kB)  | Buy Article
+
Show Abstract
The isovector dipole resonances (DR's) consisting of the giant dipole resonance and spin dipole resonance (SDR) in 4He were investigated by using the (p,p') reaction at an incident energy of 300 MeV. We compared the excitation energy, width, resonance shape and the differential cross sections for the DR in 4He with those for the DR's in 6Li and 7Li which had been observed and interpreted in earlier work as the DR's in the alpha clusters of 6Li and 7Li. The DR's in 4He and in the alpha clusters of 6,7Li were observed at Ex=25.1±0.5,28.0±0.5, and 30.5±0.5 MeV with the widths of 11.0±2.0,11.7±1.5, and 11.3±2.0 MeV, respectively. The peaks corresponding to the 2- SDR in the alpha cluster were not as dominant as that observed in 4He at Ex=22.1 MeV. The resonance shapes for the alpha cluster in 6,7Li were reproduced well with the DR shape without including the 2- SDR in 4He. The excitation energies for the DR's in the alpha clusters slightly increase with the number of the surrounding nucleons. The cross sections for the excitation of the DR's in the alpha clusters of 6,7Li, normalized to the spectroscopic factors for the alpha particle in 6,7Li, are comparable to the cross section for the excitation of the DR in 4He.

Solution of the Bohr Hamiltonian for soft triaxial nuclei
L. Fortunato, S. De Baerdemacker, and K. Heyde
Published 17 July 2006 (11 pages)
014310  Full Text: PDF (264 kB)  | Buy Article
+
Show Abstract
The Bohr-Mottelson model is solved for a generic soft triaxial nucleus, separating the Bohr Hamiltonian exactly and using a number of different model potentials: a displaced harmonic oscillator in gamma, which is solved with an approximated algebraic technique; and Coulomb/Kratzer, harmonic/Davidson, and infinite square-well potentials in beta, which are solved exactly. In each case we derive analytic expressions for the eigenenergies, which are then used to calculate energy spectra. Here we study the chain of osmium isotopes and compare our results with experimental information and previous calculations.

Study of the neutron-rich nucleus 36Si
X. Liang et al.
Published 17 July 2006 (7 pages)
014311  Full Text: PDF (264 kB)  | Buy Article
+
Show Abstract
Excited states of N=22 36Si, populated in deep-inelastic processes produced by the interaction of a 215 MeV beam of 36S ions with a 208Pb target, were studied in the present work. gamma rays from the binary fragments detected using CLARA, an array of 25 Ge Clover detectors, were measured in coincidence with projectile-like fragments detected by PRISMA, a large solid angle magnetic spectrometer. Two new gamma-ray photopeaks at energies of 1442 and 842 keV were observed and tentatively assigned to the 4+-->2+ and 6+-->4+ transitions, respectively. The systematics of the level structures of N=22 isotones are presented, and a comparison is made of the behavior of Si, Mg, and S isotopes. The level structure of 36Si is also compared with the results of sdpf shell model calculations.

alpha-decay half-lives of superheavy nuclei
Dorin N. Poenaru, Ileana-Hania Plonski, and Walter Greiner
Published 21 July 2006 (5 pages)
014312  Full Text: PDF (273 kB)  | Buy Article
+
Show Abstract
The half-lives against alpha decay of transuranium nuclei including superheavies are calculated by three methods: a semiempirical formula taking into account the magic numbers of nucleons, the analytical superasymmetric fission model, and the universal curves. The calculations based on Q values determined by using the recently published compilations of atomic masses are compared to the experimental results.

beta-decay studies of neutron-rich K isotopes
F. Perrot, F. Maréchal, C. Jollet, Ph. Dessagne, J.-C. Angélique, G. Ban, P. Baumann, F. Benrachi, U. Bergmann, C. Borcea, A. Buta, J. Cederkall, S. Courtin, J.-M. Daugas, L. M. Fraile, S. Grévy, A. Jokinen, F. R. Lecolley, E. Liénard, G. Le Scornet, V. Méot, Ch. Miehé, F. Negoita, N. A. Orr, S. Pietri, E. Poirier, M. Ramdhane, O. Roig, I. Stefan, and W. Wang
Published 21 July 2006 (18 pages)
014313  Full Text: PDF (617 kB)  | Buy Article
+
Show Abstract
The beta decay of the neutron-rich nuclei 51-53K has been used to populate bound and unbound states in 50-53Ca. Measurements of gamma rays as well as beta-delayed neutrons enabled detailed decay schemes to be established and levels identified in 50-53Ca. A delayed one-neutron emission probability P1n of 63±8% was determined for the decay of 51K. A total of seven new gamma transitions were observed following the decay of 51K, and 25 neutron branches were found that enrich the level scheme of 51Ca. Delayed neutron emission probabilities of P1n=74.4±9.3% and P2n=2.3±0.3% were determined for the decay of 52K, and 12 new gamma transitions were observed in 50,51,52Ca. Three new gamma transitions were observed in 52,53Ca following the beta decay of 53K. New limits on the P1n and P2n values were determined for the beta decay of 53K, and a decay scheme was established for 53Ca for the first time. The data obtained here should help clarify the structure of neutron-rich fp-shell nuclei around the N=32-34 subshell closures.

Level density of 56Fe and low-energy enhancement of gamma-strength function
A. V. Voinov, S. M. Grimes, U. Agvaanluvsan, E. Algin, T. Belgya, C. R. Brune, M. Guttormsen, M. J. Hornish, T. Massey, G. E. Mitchell, J. Rekstad, A. Schiller, and S. Siem
Published 26 July 2006 (6 pages)
014314  Full Text: PDF (265 kB)  | Buy Article
+
Show Abstract
The 55Mn(d,n)56Fe differential cross section is measured at Ed=7 MeV. The 56Fe level density obtained from neutron evaporation spectra is compared to the level density extracted from the 57Fe(3He, alphagamma)56Fe reaction by the Oslo-type technique. Good agreement is found between the level densities determined by the two methods. With the level density function obtained from the neutron evaporation spectra, the 56Fe gamma-strength function is also determined from the first-generation gamma matrix of the Oslo experiment. The good agreement between the past and present results for the gamma-strength function supports the validity of both methods and is consistent with the low-energy enhancement of the gamma strength below ~4 MeV that was first discovered by the Oslo method in iron and molybdenum isotopes.

Nuclear electromagnetic current in the relativistic approach with the momentum-dependent self-energies
Tomoyuki Maruyama and Satoshi Chiba
Published 26 July 2006 (12 pages)
014315  Full Text: PDF (261 kB)  | Buy Article
+
Show Abstract
We define the new description of the electromagnetic current to hold the current conservation in the momentum-dependent Dirac fields from the Ward identity. To describe the momentum dependence we solve the relativistic Hartree-Fock approximation by using the one-pion exchange. In addition we discuss on contribution from the one-pion exchange current and the core polarization. It is shown that the one-pion exchange current can reduce the convection current in the isovector case, whose value has been too large because of the small effective mass in the usual relativistic Hartree approximation.

Decay modes of 250No
D. Peterson, B. B. Back, R. V. F. Janssens, T. L. Khoo, C. J. Lister, D. Seweryniak, I. Ahmad, M. P. Carpenter, C. N. Davids, A. A. Hecht, C. L. Jiang, T. Lauritsen, X. Wang, S. Zhu, F. G. Kondev, A. Heinz, J. Qian, R. Winkler, P. Chowdhury, S. K. Tandel, and U. S. Tandel
Published 28 July 2006 (9 pages)
014316  Full Text: PDF (198 kB)  | Buy Article
+
Show Abstract
The fragment mass analyzer at the ATLAS facility has been used to unambiguously identify the mass number associated with different decay modes of the nobelium isotopes produced via 204Pb(48Ca,xn)252-xNo reactions. Isotopically pure (>99.7%) 204Pb targets were used to reduce background from more favored reactions on heavier lead isotopes. Two spontaneous fission half-lives (t1/2=3.7-0.8<sup>+1.1</sup> and 43-15<sup>+22</sup> µs) were deduced from a total of 158 fission events. Both decays originate from 250No rather than from neighboring isotopes as previously suggested. The longer activity most likely corresponds to a K isomer in this nucleus. No conclusive evidence for an alpha branch was observed, resulting in upper limits of 2.1% for the shorter lifetime and 3.4% for the longer activity.

Three-body force rearrangement effect on single particle properties in neutron-rich nuclear matter
W. Zuo, U. Lombardo, H.-J. Schulze, and Z. H. Li
Published 28 July 2006 (10 pages)
014317  Full Text: PDF (287 kB)  | Buy Article
+
Show Abstract
We extend the Brueckner-Hartree-Fock (BHF) approach to include the three-body force (TBF) rearrangement contribution in calculating the neutron and proton single particle (s.p.) properties in isospin asymmetric nuclear matter. We investigate the TBF rearrangement effect on the momentum-dependence of neutron and proton s.p. potentials, the isospin splitting and especially its density dependence of the neutron and proton effective masses, and the isospin symmetry potential in neutron-rich nuclear matter by adopting the realistic Argonne V18 two-body nucleon-nucleon interaction supplemented with a microscopic TBF. We find that at low densities, the TBF rearrangement effect is fairly weak, whereas the TBF induces a significant rearrangement effect on the s.p. properties at high densities and large momenta. The TBF rearrangement contribution to s.p. potential is shown to be repulsive, and it reduces considerably the attraction of the BHF s.p. potential. The repulsion from the TBF rearrangement turns out to be strongly momentum dependent at high densities and high momenta. As a consequence, it enhances remarkably the momentum dependence of the proton and neutron s.p. potentials and reduces the neutron and proton effective masses. At low densities, the TBF rearrangement effect on symmetry potential is almost negligible, while at high densities, it enlarges sizably the symmetry potential. At high enough densities, it may even change the high-momentum behavior of symmetry potential. In both cases, with and without including the TBF rearrangement contribution, the predicted neutron effective mass is larger than the proton one in neutron-rich matter within the BHF framework; i.e., the predicted isospin splitting of the proton and neutron effective masses in neutron-rich matter is such that mn<sup>*</sup>>=mp<sup>*</sup>, in agreement with the recent Dirac-BHF predictions. The TBF rearrangement contribution reduces remarkably the magnitude of the proton-neutron effective mass splitting at high densities. At high enough densities, inclusion of the TBF rearrangement contribution even suppresses almost completely the effective mass splitting.

Collective multipole excitations based on correlated realistic nucleon-nucleon interactions
N. Paar, P. Papakonstantinou, H. Hergert, and R. Roth
Published 31 July 2006 (14 pages)
014318  Full Text: PDF (1086 kB)  | Buy Article
+
Show Abstract
We investigate collective multipole excitations for closed-shell nuclei from 16O to 208Pb by using correlated realistic nucleon-nucleon interactions in the framework of the random phase approximation (RPA). The dominant short-range central and tensor correlations are treated explicitly within the unitary correlation operator method (UCOM), which provides a phase-shift-equivalent correlated interaction VUCOM adapted to simple uncorrelated Hilbert spaces. The same unitary transformation that defines the correlated interaction is used to derive correlated transition operators. Using VUCOM, we solve the Hartree-Fock (HF) problem and employ the single-particle states as a starting point for the RPA. By construction, the UCOM-RPA is fully self-consistent, i.e., the same correlated nucleon-nucleon interaction is used in calculations of the HF ground state and in the residual RPA interaction. Consequently, the spurious state associated with the center-of-mass motion is properly removed, and the sum rules are exhausted within ±3%. The UCOM-RPA scheme results in a collective character of giant monopole, dipole, and quadrupole resonances in closed-shell nuclei across the nuclear chart. For the isoscalar giant monopole resonance, the resonance energies are in agreement with experiment, hinting at a reasonable compressibility. However, in the 1- and 2+ channels the resonance energies are overestimated because of missing long-range correlations and three-body contributions.

Nuclear Reactions

Bound single-particle states for neutrons from a global spherical optical model
B. Morillon and P. Romain
Published 7 July 2006 (6 pages)
014601  Full Text: PDF (316 kB)  | Buy Article
+
Show Abstract
The bound single-particle states for neutrons are calculated from our previous global spherical optical model potential containing dispersive terms and a local energy approximation. Reasonably good results are obtained for the single-particle states as well as for the neutron binding energies. This constitutes a further test of our potential.

Elliptic flow and system size dependence of transition energies at intermediate energies
Yingxun Zhang and Zhuxia Li
Published 7 July 2006 (5 pages)
014602  Full Text: PDF (617 kB)  | Buy Article
+
Show Abstract
The elliptic flow for Z<=2 particles in heavy ion collisions at energies from several tens to several hundreds MeV per nucleon is investigated by means of a transport model, i.e., a new version of the improved quantum molecular dynamics model (ImQMD05). This model employs a complete Skyrme potential energy density functional. The influence of different effective interactions and medium corrections of nucleon-nucleon cross sections on the elliptic flow are studied. Our results show that a soft nuclear equation of state and incident energy dependent in-medium nucleon-nucleon cross sections are required to describe the excitation function of the elliptic flow at intermediate energies. The size dependence of transition energies for the elliptic flow at intermediate energies is also studied. The system size dependence of transition energies fits a power of system size with an exponent of 0.223.

Continuum spectroscopy of Borromean two-neutron halo nuclei
S. N. Ershov, B. V. Danilin, and J. S. Vaagen
Published 11 July 2006 (10 pages)
014603  Full Text: PDF (617 kB)  | Buy Article
+
Show Abstract
Energy and angular correlation distributions of the three fragments in 6He breakup on 208Pb at a collision energy of 240 MeV/nucleon are discussed within the microscopic four-body distorted wave model and compared with experimental data. The nuclear structure of the ground state and low-energy three-body continuum of 6He is calculated by the method of hyperspherical harmonics within the three-body cluster model. Reflections of the fundamental permutation symmetry of the halo neutrons in angular and energy correlations are pointed out. The calculations describe the experimental data for fragment correlations near breakup threshold rather well, and the physics is contained in a few elementary modes; but with increasing excitation energy of 6He, some striking deviations from experimental distributions are encountered. Possible reasons for this are discussed.

In-flight (K-,p) reactions for the formation of kaonic atoms and kaonic nuclei using the Green function method
J. Yamagata, H. Nagahiro, and S. Hirenzaki
Published 14 July 2006 (9 pages)
014604  Full Text: PDF (617 kB)  | Buy Article
+
Show Abstract
We study theoretically the kaonic atom and kaonic nucleus formations in the in-flight (K-,p) reactions using the Green function method, which is suited to evaluate formation rates both of stable and unstable bound systems. We consider 12C and 16O as the targets and calculate the spectra of the (K-,p) reactions. We conclude that no peak structure resulting from kaonic nucleus formation is expected in the reaction spectra calculated with the chiral unitary kaon-nucleus optical potential. In the spectra with the phenomenological deep kaon-nucleus potential, it may be possible to observe some structures because of the formation of the kaonic nucleus states. For all cases, we find clear signals because of the kaonic atom formations in the reaction spectra, which show very interesting structures, such as the RESONANCE DIP instead of the resonance peak for the atomic 1s state formation.

Reaction and proton-removal cross sections of 6Li, 7Be, 10B, 9,10,11C, 12N, 13,15O, and 17Ne on Si at 15 to 53 MeV/nucleon
R. E. Warner, F. Carstoiu, J. A. Brown, F. D. Becchetti, D. A. Roberts, B. Davids, A. Galonsky, R. M. Ronningen, M. Steiner, M. Horoi, J. J. Kolata, A. Nadasen, C. Samanta, J. Schwartzenberg, and K. Subotic
Published 17 July 2006 (12 pages)
014605  Full Text: PDF (617 kB)  | Buy Article
+
Show Abstract
Excitation functions for total reaction cross sections, sigmaR, were measured for the light, mainly proton-rich nuclei 6Li, 7Be, 10B, 9,10,11C, 12N, 13,15O, and 17Ne incident on a Si telescope at energies between 15 and 53 MeV/nucleon. The telescope served as target, energy degrader and detector. Proton-removal cross sections, sigma2p for 17Ne and sigmap for most of the other projectiles, were also measured. The strong absorption model reproduces the A-dependence of sigmaR, but not the detailed structure. Glauber multiple scattering theory and the Jeukenne, Lejeune, and Mahaux (JLM) folding model provided improved descriptions of the measured sigmaR values. Rms radii, extracted from the measured sigmaR using the optical limit of Glauber theory, are in good agreement with those obtained from high energy data. One-proton removal reactions are described using an extended Glauber model, incorporating second order noneikonal corrections, realistic single particle densities, and spectroscopic factors from shell model calculations.

Extended continuum discretized coupled channels method: Core excitation in the breakup of exotic nuclei
N. C. Summers, F. M. Nunes, and I. J. Thompson
Published 20 July 2006 (12 pages)
014606  Full Text: PDF (240 kB)  | Buy Article
+
Show Abstract
The extended continuum discretized coupled channel (XCDCC) method is developed to treat reactions where core degrees of freedom play a role. The projectile is treated as a multi-configuration coupled channels system generated from a valence particle coupled to a deformed core which is allowed to excite. The coupled channels initial state breaks up into a coupled channels continuum which is discretized into bins, similarly to the original CDCC method. Core collective degrees of freedom are also included in the interaction of the core and the target, so that dynamical effects can occur during the reaction. We present results for the breakup of 17C=16C+n and 11Be=10Be+n on 9Be. Results show that the total cross section increases with core deformation. More importantly, the relative percentage of the various components of the initial state are modified during the reaction process through dynamical effects. This implies that comparing spectroscopic factors from structure calculations with experimental cross sections requires more detailed reaction models that go beyond the single particle model.

Energy dependence of nuclear charge distribution in neutron induced fission of Z-even nuclei
V. A. Roshchenko, V. M. Piksaikin, S. G. Isaev, and A. A. Goverdovski
Published 21 July 2006 (11 pages)
014607  Full Text: PDF (286 kB)  | Buy Article
+
Show Abstract
For the first time the distribution of nuclear charge of fission products with mass numbers 87, 88, 89, 91, 93, 94, 95, 137, 138, 139, and 140 and their complementary products have been studied for neutron induced fission of 235U and 239Pu in the energy range from thermal up to 1.2 MeV. The energy dependences of the cumulative yields of 87Br, 88Br, 89Br, 91Br, 93Kr, 94Rb, 95Rb, 137I, 138I, 139I, and 140I have been obtained by delayed neutron measurements. The most probable charge ZP(A)in the appropriate isobaric beta-decay chains was estimated. The results were analyzed in terms of the deviation DeltaZP(A') of the most probable charge of isobaric beta-decay chains from the unchanged charge distribution before prompt neutron emission (nuclear charge polarization) and they are compared with experimental data of other authors and with predictions from Nethaway's ZP-formula and Wahl's ZP-model. We show that the nuclear charge polarization of primary fission fragments <DeltaZP(A')> before prompt neutron evaporation decreases as the excitation energy of the compound nucleus increases. This decrease is more pronounced for fission of 235U. The energy dependencies of DeltaZP(A') and DeltaZP(ZP) obtained in the present work show an attenuation of the odd-even effects in the charge distribution as the excitation energy of the compound nucleus increases.

Fission of light actinides: 232Th(n,f) and 231Pa(n,f) reactions
M. Sin, R. Capote, A. Ventura, M. Herman, and P. OblozinskÝ
Published 27 July 2006 (13 pages)
014608  Full Text: PDF (612 kB)  | Buy Article
+
Show Abstract
A model to describe fission on light actinides, which takes into account transmission through a triple-humped fission barrier with absorption, is proposed. The fission probability derived in the WKB approximation within an optical model for fission has been incorporated into the statistical model of nuclear reactions. The complex resonant structure in the first-chance neutron-induced fission cross sections of 232Th and 231Pa nuclei has been reproduced by the proposed model. Consistent sets of parameters describing the triple-humped fission barriers of 233Th and 232Pa have been obtained. The results confirm the attribution of the gross resonant structure in the fission probability of these light actinides to partially damped vibrational states in the second well and undamped vibrational states in the third well of the corresponding fission barriers.

Transient and quasistationary dissipative effects in the fission flux across the barrier in 1A GeV 238U on deuterium reactions
J. Benlliure, E. Casarejos, J. Pereira, and K.-H. Schmidt
Published 27 July 2006 (9 pages)
014609  Full Text: PDF (380 kB)  | Buy Article
+
Show Abstract
Isotopic cross sections of all projectile residues with Z above 23 produced in collisions induced by 238U at 1A GeV on deuterium have been measured. The isotopic distributions reflect the role of evaporation and fission in the formation process of these nuclei. The comparison of the measured cross sections with Monte Carlo deexcitation codes including an analytical description of the dynamics of fission shows the sensitivity of the data to nuclear dissipation. Moreover, the large excitation-energy range covered in this experiment together with the high accuracy of the measured cross sections allowed to clearly separate and quantify the role of transient and quasistationary dissipative effects in the fission-decay width.

Fusion-fission studies in the 20Ne+181Ta reaction at E/A=7.5 and 9 MeV/nucleon
R. Tripathi, K. Sudarshan, A. Goswami, R. Guin, and A. V. R. Reddy
Published 27 July 2006 (11 pages)
014610  Full Text: PDF (329 kB)  | Buy Article
+
Show Abstract
Mass and mass resolved angular distribution of the fission products have been measured in the 20Ne+181Ta reaction at Elab=150 and 180 MeV using recoil catcher technique followed by off-line gamma-ray spectrometry. Recoil range distribution (RRD) of the evaporation residues (ERs) have been measured at Elab=180 MeV. Due to high angular momentum of the fissioning nucleus, variances of the mass distribution in the present system have been found to be higher than those in similar systems involving comparatively less angular momentum. Significant contribution from noncompound nucleus processes such as deep inelastic collisions (DIC) and incomplete fusion reaction (ICF) is expected in the present system due to high angular momentum. The code HICOL predicts that the noncompound nucleus process would result in fission like events. In the present study, experimental fission cross sections are in reasonably good agreement with the calculation of statistical model code PACE2. Measurement of the ER cross section indicates significant contribution from the ICF reaction. The recoil range distributions of the ERs could resolve the complete fusion (CF) and ICF channels and were used to obtain ICF cross section. The experimentally measured ICF cross section accounts for almost entire cross section between lcrit and lmax, indicating ICF reaction to be the dominant non-compound nucleus process at beam energies of the present study. DIC products could not be detected at both the beam energies. At these beam energies, the entrance channel pocket configuration for many collision trajectories is expected to be more elongated compared to the unconditional saddle point and, therefore, significant contribution form noncompound nucleus fission (i.e., fission without passing through the unconditional saddle point) is expected. However, the experimental anisotropies of fission products could be reproduced by the statistical theory calculation after considering the change in the saddle point shape with angular momentum of the fissioning nucleus. No correlation between the angular anisotropy and mass asymmetry of the fission products was observed in the present study.

Isobaric cold-fusion channels for synthesis of 276114, 286114, and 290114
R. A. Gherghescu and Y. Nagame
Published 27 July 2006 (12 pages)
014611  Full Text: PDF (1060 kB)  | Buy Article
+
Show Abstract
Cold-fusion reactions are investigated with the goal of synthesizing 276114, 286114, and 290114 elements. Potential energy surfaces are calculated as the result of dynamic minimization with independent deformations of the target and projectile, small semiaxis of the projectile, and distance between centers as degrees of freedom. An advanced binary macroscopic-microscopic method is used to obtain the deformation energy, and the Werner-Wheeler approximation yields the mass tensor. The charge asymmetry is varied for the same mass asymmetry channel belonging to an energy valley. The highest penetrability values are obtained for cold-fusion channels within 116,118Cd projectiles leading to 276114; 142Ba projectile for 286114; and 104Kr, 108Sr, and 112Zr leading to 290114.

Nuclear liquid-gas phase transition studied with antisymmetrized molecular dynamics
Takuya Furuta and Akira Ono
Published 31 July 2006 (13 pages)
014612  Full Text: PDF (391 kB)  | Buy Article
+
Show Abstract
The nuclear liquid-gas phase transition of the system in ideal thermal equilibrium is studied with antisymmetrized molecular dynamics. The time evolution of a many-nucleon system confined in a container is solved for a long time to get a microcanonical ensemble of a given energy and volume. The temperature and the pressure are extracted from this ensemble and the caloric curves are constructed. The present work is the first time that a microscopic dynamical model which describes nuclear multifragmentation reactions well is directly applied to get the nuclear caloric curve. The obtained constant pressure caloric curves clearly show the characteristic feature of the liquid-gas phase transition, namely negative heat capacity (backbending), which is expected for the phase transition in finite systems.

Relativistic Nuclear Collisions

Origins of bulk viscosity in relativistic heavy ion collisions
Kerstin Paech and Scott Pratt
Published 7 July 2006 (7 pages)
014901  Full Text: PDF (286 kB)  | Buy Article
+
Show Abstract
A variety of physical phenomena can lead to viscous effects. Several sources of shear and bulk viscosity are reviewed with an emphasis on the bulk viscosity associated with chiral restoration and with chemical nonequilibrium. We show that in linear response approximation and in a mean field treatment of the limiting case of a second-order phase transition, the bulk viscosity peaks in a singularity at the critical point.

Reconstructing rho0 and omega mesons from nonleptonic decays in C+C collisions at 2 GeV/nucleon in transport model calculations
Sascha Vogel and Marcus Bleicher
Published 19 July 2006 (5 pages)
014902  Full Text: PDF (286 kB)  | Buy Article
+
Show Abstract
We predict transverse and longitudinal momentum spectra and yields of rho0 and omega mesons reconstructed from hadron correlations in C+C reactions at 2 GeV/nucleon. The rapidity and pT distributions for reconstructable rho0 mesons differs strongly from the primary distribution, while the omega distributions are only weakly modified. We discuss the temporal and spatial distributions of the particles emitted in the hadron channel. Finally, we report on the mass shift of the rho0 due to its coupling to the N*(1520), which is observable in both the dilepton and pipi channel. Our calculations can be compared to the Hades experiment at GSI, Darmstadt.

High momentum dilepton production from jets in a quark gluon plasma
Simon Turbide, Charles Gale, Dinesh K. Srivastava, and Rainer J. Fries
Published 28 July 2006 (15 pages)
014903  Full Text: PDF (368 kB)  | Buy Article
+
Show Abstract
We discuss the emission of high momentum lepton pairs (pT>4 GeV) in central Au+Au collisions at RHIC (sqrt(s[sub NN])=200 GeV) and Pb+Pb collisions at the LHC (sqrt(s[sub NN])=5500 GeV). Yields of dileptons produced through interactions of jets with thermal partons have been calculated, with next-to-leading order corrections through hard thermal loop (HTL) resummation. They are compared to thermal dilepton emission and the Drell-Yan process. A complete leading order treatment of jet energy loss has been included. Jet-plasma interactions are found to dominate over thermal dilepton emission for all values of the invariant mass M. Drell-Yan is the dominant source of high momentum lepton pairs for M>3 GeV at RHIC, after the background from heavy quark decays is subtracted. At LHC, the range M<7 GeV is dominated by jet-plasma interactions. Effects from jet energy loss on jet-plasma interactions turn out to be weak, but non-negligible, reducing the yield of low-mass dileptons by about 30%.

Hadronic Physics and QCD

Density dependent parametrization models: Formalism and applications
S. S. Avancini and D. P. Menezes
Published 5 July 2006 (14 pages)
015201  Full Text: PDF (286 kB)  | Buy Article
+
Show Abstract
In this work we derive a formalism to incorporate asymmetry and temperature effects in the Brown-Rho (BR) scaled Lagrangian model in a mean field theory. The Lagrangian density discussed in this work requires less parameters than the usual models with density dependent couplings. We also present the formalism with the inclusion of the eight lightest baryons, two lightest leptons, beta equilibrium and charge neutrality in order to apply the BR scaled model to the study of neutron stars. The results are again compared with the ones obtained from another density dependent parametrization model. The role played by the rearrangement term at T=0 for nuclear or neutron star matter and at finite temperature is investigated. The BR scaled model is shown to be a good tool in studies involving density dependent effective masses and in astrophysics applications.

Role of q[overline q] components in the N(1440) resonance
Q. B. Li and D. O. Riska
Published 11 July 2006 (10 pages)
015202  Full Text: PDF (286 kB)  | Buy Article
+
Show Abstract
The role of 5-quark components in the pion and electromagnetic decays and transition form factors of the N(1440) resonance is explored. The qqqq[overline q] components, where the 4-quark subsystem has the flavor-spin symmetries [4]FS[22]F[22]S and [4]FS[31]F[31]S, which are expected to have the lowest energy of all qqqq[overline q] configurations, are considered in detail with a nonrelativistic quark model. The matrix elements between the 5-quark components of the N(1440) and the nucleon, qqqq[overline q]-->qqqq[overline q], play a minor role in these decays, whereas the transition matrix elements qqqq[overline q]-->qqq and qqq-->qqqq[overline q] that involve quark antiquark annihilation are very significant. Both for electromagnetic and strong decays the change from the valence quark model value is dominated by the confinement triggered q[overline q] annihilation transitions. In the case of pion decay the calculated decay width is enhanced substantially both by the direct q[overline q]-->pi and also by the confinement triggered q[overline q]-->pi transitions. Agreement with the empirical value for the pion decay width may be reached with a ~30%   qqqq[overline q] component in the N(1440).

Chiral approach to antikaon s- and p-wave interactions in dense nuclear matter
L. Tolós, A. Ramos, and E. Oset
Published 12 July 2006 (14 pages)
015203  Full Text: PDF (286 kB)  | Buy Article
+
Show Abstract
The properties of the antikaons in nuclear matter are investigated from a chiral unitary approach which incorporates the s- and p-waves of the [overline K]N interaction. To obtain the in-medium meson-baryon amplitudes we include, in a self-consistent way, Pauli blocking effects, meson self-energies corrected by nuclear short-range correlations and baryon binding potentials. We pay special attention to investigating the validity of the on-shell factorization, showing that it cannot be applied in the evaluation of the in-medium corrections to the p-wave amplitudes. In nuclear matter at saturation energy, the Lambda and Sigma develop an attractive potential of about –30 MeV, while the Sigma* pole remains at the free space value although its width gets sensibly increased to about 80 MeV. The antikaon also develops a moderate attraction that does not support the existence of very deep and narrow bound states, confirming the findings of previous self-consistent calculations.

Isospin violation in the vector form factors of the nucleon
Bastian Kubis and Randy Lewis
Published 14 July 2006 (12 pages)
015204  Full Text: PDF (286 kB)  | Buy Article
+
Show Abstract
A quantitative understanding of isospin violation is an increasingly important ingredient in the extraction of the nucleon's strange vector form factors from experimental data. We calculate the isospin-violating electric and magnetic form factors in chiral perturbation theory to leading and next-to-leading order, and we extract the low-energy constants from resonance saturation. Uncertainties are dominated largely by limitations in the current knowledge of some vector meson couplings. The resulting bounds on isospin violation are sufficiently precise to be of value to on-going experimental studies of the strange form factors.

Channel coupling effects in rho-meson photoproduction
A. Usov and O. Scholten
Published 21 July 2006 (7 pages)
015205  Full Text: PDF (606 kB)  | Buy Article
+
Show Abstract
We investigate rho-meson photoproduction in a coupled-channels formulation. It is shown that channel coupling effects are large and account for discrepancies observed in several single-channel treatments.

Experimental determination of the complete spin structure for [overline p]p-->[overline Lambda ]Lambda at p<sub>[overline p]</sub>=1.637  GeV/c
K. D. Paschke et al. (PS185 Collaboration)
Published 25 July 2006 (21 pages)
015206  Full Text: PDF (1134 kB)  | Buy Article
+
Show Abstract
The reaction [overline p]p-->[overline Lambda ]Lambda-->[overline p]pi+ppi- has been measured with high statistics at a beam momentum of p[overline p]=1.637GeV/c. The use of a transversely polarized frozen-spin target combined with the self-analyzing property of Lambda/[overline Lambda ] decay allows access to unprecedented information on the spin structure of the interaction. The most general spin-scattering matrix can be written in terms of 11 real parameters for each bin of scattering angle; each of these parameters is determined with reasonable precision. From these results, all conceivable spin correlations are determined with inherent self-consistency. Good agreement is found with the few previously existing measurements of spin observables in [overline p]p-->[overline Lambda ]Lambda near this energy. Existing theoretical models do not give good predictions for those spin observables that had not been previously measured.

Critical analysis on deeply bound kaonic states in nuclei
E. Oset and H. Toki
Published 26 July 2006 (9 pages)
015207  Full Text: PDF (279 kB)  | Buy Article
+
Show Abstract
We make a critical analysis of the theoretical calculations that lead to predictions of deeply bound kaonic states in nuclei. The model setup, after dropping several important processes and channels, leads unavoidably to an unrealistic deep potential with a very small imaginary part. We review also the experimental results taken as reference for the claim of deeply bound kaons. We suggest that the peaks of the proton spectra come from K- absorption on a pair of nucleons, leaving the rest of the nucleons as spectators. Based on this conjecture, we predict what would happen in other nuclei.

Scalar kappa meson in K* photoproduction
Yongseok Oh and Hungchong Kim
Published 28 July 2006 (5 pages)
015208  Full Text: PDF (153 kB)  | Buy Article
+
Show Abstract
We propose that the scalar kappa(800) meson may play an important role in K* photoproduction. In the reactions of gammap-->K*+Lambda and gammap-->K*0Sigma+, we consider the production mechanisms including t-channel K*,K,kappa exchanges, s-channel N,Delta diagrams, and u-channel Lambda,Sigma,Sigma* diagrams within the tree level approximation, and find that the kappa-meson exchange may contribute significantly to K*Sigma photoproduction, while it is rather supplementary in K*Lambda photoproduction. We demonstrate how the observables of K* photoproduction can be used to constrain the kappa meson properties. In particular, the parity asymmetry can separate the kappa meson contribution in K* photoproduction.

Electroweak Interaction, Symmetries

Branching ratios for the beta decay of 21Na
V. E. Iacob, J. C. Hardy, C. A. Gagliardi, J. Goodwin, N. Nica, H. I. Park, G. Tabacaru, L. Trache, R. E. Tribble, Y. Zhai, and I. S. Towner
Published 14 July 2006 (6 pages)
015501  Full Text: PDF (150 kB)  | Buy Article
See Also: Erratum
+
Show Abstract
We have measured the beta-decay branching ratio for the transition from 21Na to the first excited state of 21Ne. A recently published test of the standard model, which was based on a measurement of the beta-nu correlation in the decay of 21Na, depended on this branching ratio. However, until now only relatively imprecise (and, in some cases, contradictory) values existed for it. Our new result, 4.74(4)%, reduces but does not remove the reported discrepancy with the standard model.

General study of superscaling in quasielastic (e,e') and (nu,µ) reactions using the relativistic impulse approximation
J. A. Caballero
Published 21 July 2006 (12 pages)
015502  Full Text: PDF (503 kB)  | Buy Article
+
Show Abstract
The phenomenon of superscaling for quasielastic lepton induced reactions at energies of a few GeV is investigated within the framework of the relativistic impulse approximation. A global analysis of quasielastic inclusive electron and charged-current neutrino scattering reactions on nuclei is presented. Scaling and superscaling properties are shown to emerge from both types of processes. The crucial role played by final state interactions is evaluated by using different approaches. The asymmetric shape presented by the experimental scaling function, with a long tail in the region of positive values of the scaling variable, is reproduced when the interaction in the final state between the knockout nucleon and the residual nucleus is described within the relativistic mean field approach. The impact of gauge ambiguities and off-shell effects in the scaling function is also analyzed.

Nuclear Astrophysics

Neutron star equation of state and the possibility of complex self-energy in Landau theory of a Fermi liquid in the presence of a strong, quantizing magnetic field
Soma Mandal, Roni Saha, Sutapa Ghosh, and Somenath Chakrabarty
Published 12 July 2006 (12 pages)
015801  Full Text: PDF (503 kB)  | Buy Article
+
Show Abstract
Using the relativistic version of Landau theory of Fermi liquid with sigma-omega and rho mesons exchange, we have obtained an equation state for dense neutron star matter in the presence of a strong, quantizing magnetic field. It is found that in this scenario the self-energies of both neutron and proton components of dense neutron star matter become complex under certain physical conditions. To be more specific, it is observed that in the exchange diagrams of sigma,omega and neutral rho transfer processes and in the direct interaction diagram with rho± transfer reactions, the nucleon self-energies become complex in nature.

Two-neutron capture reactions and the r process
Amy Bartlett, Joachim Görres, Grant J. Mathews, Kaori Otsuki, Michael Wiescher, Dieter Frekers, Alberto Mengoni, and Jeffrey Tostevin
Published 12 July 2006 (8 pages)
015802  Full Text: PDF (503 kB)  | Buy Article
+
Show Abstract
Rates for the 4He(2n,gamma)6He and 6He(alpha,n)9Be reactions have been calculated, including both resonant and nonresonant contributions. The sequential two-neutron capture process on 4He has also been reevaluated on the basis of new experimental results. It is shown that a one-step dineutron capture reaction may enhance the sequential two-neutron reaction rate by several orders of magnitude. This opens the possibility that reaction flow through 4He(2n,gamma)6He(alpha,n)9Be may occur in competition with the bottle-neck three-body reactions 4He(2alpha,gamma)12C and the 4He(alphan,gamma)9Be that initiate the alpha process and provide seed nuclei for the r process. Here we explore the effect of such dineutron capture on r-process nucleosynthesis. We show that such reactions have little effect on the final abundance and would change only r-process abundances in an extremely neutron-rich low-temperature r process.

Direct measurement of supernova neutrino emission parameters with a gadolinium-enhanced Super-Kamiokande detector
Hasan Yüksel, Shin'ichiro Ando, and John F. Beacom
Published 13 July 2006 (5 pages)
015803  Full Text: PDF (503 kB)  | Buy Article
+
Show Abstract
The time-integrated luminosity and average energy of the neutrino emission spectrum are essential diagnostics of core-collapse supernovae. The SN 1987A electron antineutrino observations by the Kamiokande-II and IMB detectors are only roughly consistent with each other and theory. Using new measurements of the star formation rate history, we reinterpret the Super-Kamiokande upper bound on the electron antineutrino flux from all past supernovae as an excluded region in neutrino emission parameter space. A gadolinium-enhanced Super-Kamiokande should be able to jointly measure these parameters, and a future megaton-scale detector would enable precision studies.

Astrophysical S factor for the 11B(d,n)12C reaction below 135 keV
Y. Parpottas, M. W. Ahmed, M. A. Blackston, R. H. France III, B. A. Perdue, R. M. Prior, A. Sabourov, M. C. Spraker, and H. R. Weller
Published 19 July 2006 (5 pages)
015804  Full Text: PDF (364 kB)  | Buy Article
See Also: Publisher's Note
+
Show Abstract
The 11B(d,n)12C reaction was studied using deuteron beams of 120–160 keV to determine the absolute astrophysical S factors and cross sections for the n0 and n1 neutron groups. The slopes of the S factors are consistent with zero for both the n0 and n1 cases. The measured S factor for the sum of both neutron groups at c.m. energies below 135 keV is S=3180±480 keV b. A DWBA calculation is able to reproduce the ratio of the S factors found here to those obtained in a recent study of the 7Li(d,n0,1)8Be reaction.

Effects of spin-orbit interaction on nuclear response and neutrino mean free path
J. Margueron, N. Van Giai, and J. Navarro
Published 24 July 2006 (5 pages)
015805  Full Text: PDF (187 kB)  | Buy Article
+
Show Abstract
The effects of the spin-orbit component of the particle-hole interaction on nuclear response functions and neutrino mean free path are examined. A complete treatment of the full Skyrme interaction in the case of symmetric nuclear matter and pure neutron matter is given. Numerical results for neutron matter are discussed. It is shown that the effects of the spin-orbit interaction remain small, even at momentum transfer larger than the Fermi momentum. The neutrino mean free paths are marginally affected.

BRIEF REPORTS

Chiral [script O](Q4) two-body operators for s-wave pion photoproduction on the NN system
A. Gårdestig
Published 6 July 2006 (4 pages)
017001  Full Text: PDF (187 kB)  | Buy Article
+
Show Abstract
The two-body currents for s-wave pion photoproduction on the NN system are derived to [script O](Q4) in chiral perturbation theory. For the interesting case of 3S1<-->1S0 transitions, we show that an axial isovector two-nucleon contact term connects the short-distance physics of pion photoproduction to pion production and several important electroweak reactions. We also find that the standard chiral Lagrangian gives a gammapipiNN vertex that has not been explicitly mentioned in previous literature. The corresponding Feynman rule is presented here and some processes where it should be important are briefly discussed.

Stability of s-band states in the tilting calculation of 182Os
Y. Hashimoto and T. Horibata
Published 7 July 2006 (4 pages)
017301  Full Text: PDF (187 kB)  | Buy Article
+
Show Abstract
We carried out the three-dimensional cranking calculations for osmium 182Os within the Hartree-Fock-Bogoliubov framework. It turned out that the state in the g-band is stable (unstable) with respect to the tilt angle of the cranking axis when the angular momentum is below (above) a critical value. However, the states in the s-band with the angular momentum below 30[h-bar] are unstable everywhere along the band. In our model calculations, the wobbling motion does not exist on top of the s-band state characterized by the component of two aligned particles.

Candidate chiral doublet bands in the odd-odd nucleus 126Cs
Shouyu Wang, Yunzuo Liu, T. Komatsubara, Yingjun Ma, and Yuhu Zhang
Published 7 July 2006 (4 pages)
017302  Full Text: PDF (187 kB)  | Buy Article
+
Show Abstract
The candidate chiral doublet bands recently observed in 126Cs have been extended to higher spins, several new linking transitions between the two partner members of the chiral doublet bands are observed, and gamma-intensities related to the chiral doublet bands are presented by analyzing the gamma-gamma coincidence data collected earlier at the NORDBALL through the 116Cd(14N, 4n)126Cs reaction at a beam energy of 65 MeV. The intraband B(M1)/B(E2) and interband B(M1)in/B(M1)out ratios and the energy staggering parameter, S(I), have been deduced for these doublet bands. The results are found to be consistent with the chiral interpretation for the two structures. Furthermore, the observation of chiral doublet bands in 126Cs together with those in 124Cs, 128Cs, 130Cs, and 132Cs also indicates that the chiral conditions do not change rapidly with decreasing neutron number in these odd-odd Cesium isotopes.

Identification of high spin states in 100Zr
J. K. Hwang, A. V. Ramayya, J. H. Hamilton, J. O. Rasmussen, Y. X. Luo, D. Fong, K. Li, C. Goodin, S. J. Zhu, S. C. Wu, M. A. Stoyer, R. Donangelo, X.-R. Zhu, and H. Sagawa
Published 18 July 2006 (4 pages)
017303  Full Text: PDF (187 kB)  | Buy Article
+
Show Abstract
Eight new high spin states and 23 new gamma transitions have been identified in 100Zr from studies of 252Cf spontaneous fission with Gammasphere. A near-spherical excited band in 100Zr based on the 331.1 keV 0+ state is extended from 4+ up to 12+. A DeltaI=1 band with band-head energy of 2316.1 keV is extended.

alpha decay half-lives of new superheavy nuclei within a generalized liquid drop model
Hongfei Zhang, Wei Zuo, Junqing Li, and G. Royer
Published 19 July 2006 (4 pages)
017304  Full Text: PDF (187 kB)  | Buy Article
+
Show Abstract
The alpha decay half-lives of the recently produced isotopes of the 112, 114, 116 and 118 nuclei and decay products have been calculated in the quasi-molecular shape path using the experimental Qalpha value and a Generalized Liquid Drop Model including the proximity effects between nucleons in the neck or the gap between the nascent fragments. Reasonable estimates are obtained for the observed alpha decay half-lives. The results are compared with calculations using the Density-Dependent M3Y effective interaction and the Viola-Seaborg-Sobiczewski formulae. Generalized Liquid Drop Model predictions are provided for the alpha decay half-lives of other superheavy nuclei using the Finite Range Droplet Model Qalpha and compared with the values derived from the VSS formulae.

Primary versus secondary gamma intensities in 171Yb(nth,gamma)
A. Schiller, A. V. Voinov, E. Algin, L. A. Bernstein, P. E. Garrett, M. Guttormsen, R. O. Nelson, J. Rekstad, and S. Siem
Published 19 July 2006 (3 pages)
017305  Full Text: PDF (187 kB)  | Buy Article
+
Show Abstract
The two published literature values [Greenwood et al., Nucl. Phys. A252, 260 (1975) and Gelletly et al., J. Phys. G 11, 1055 (1985)] for absolute primary gamma intensities following thermal neutron capture of 171Yb differ on average by a factor of 3. We have resolved this conflict in favor of Greenwood et al. by a measurement of primary versus secondary intensities.

Search for neutron decoupling in 22O via the (d,d'gamma) reaction
Z. Elekes, Zs. Dombrádi, N. Aoi, S. Bishop, Zs. Fülöp, J. Gibelin, T. Gomi, Y. Hashimoto, N. Imai, N. Iwasa, H. Iwasaki, G. Kalinka, Y. Kondo, A. A. Korsheninnikov, K. Kurita, M. Kurokawa, N. Matsui, T. Motobayashi, T. Nakamura, T. Nakao, E. Yu. Nikolskii, T. K. Ohnishi, T. Okumura, S. Ota, A. Perera, A. Saito, H. Sakurai, Y. Satou, D. Sohler, T. Sumikama, D. Suzuki, M. Suzuki, H. Takeda, S. Takeuchi, Y. Togano, and Y. Yanagisawa
Published 19 July 2006 (3 pages)
017306  Full Text: PDF (187 kB)  | Buy Article
+
Show Abstract
We have searched for valence neutron decoupling in 22O, a phenomenon recently observed in neutron-rich C, B, and lighter O nuclei. From the cross section of the (d,d'gamma) reaction for the transition between the ground state and the first 2+ state of 22O, the neutron and proton deformation parameters have been deduced by distorted wave analysis using and reanalyzing the data of a previous Coulomb excitation measurement. The ratio of the neutron and proton multipole transition matrix elements Mn/Mp compared to the N/Z value has been derived to be around 1. This result indicates that the 22O isotope has small and similar neutron and proton deformations, which is consistent with N=14 shell closure. Thus, the concept of neutron decoupling does not hold for this nucleus.

Systematic analyses of the t+t clustering effect in He isotopes
S. Aoyama, N. Itagaki, and M. Oi
Published 20 July 2006 (4 pages)
017307  Full Text: PDF (129 kB)  | Buy Article
+
Show Abstract
A systematic study on the ground-state structure of He isotopes (including 10He) is presented through a new method developed on the basis of antisymmetrized molecular dynamics (AMD), the generator coordinate method (GCM), and the stochastic variational method (SVM). In this approach, variational calculations are carried out by means of the GCM with the AMD wave functions produced by means of the SVM. A role of the t+t cluster component is examined with the present method, allowing the wider configuration space containing simultaneously the "t+t+valence neutrons" structure and "4He+valence neutrons" structure.

Absolute branching intensities in the decay of 92Rb to 92Sr
G. Lhersonneau, V. Rizzi, O. Alyakrinskiy, A. Lanchais, L. B. Teccchio, A. E. Barzakh, D. V. Fedorov, A. M. Ionan, V. S. Ivanov, K. A. Mezilev, F. V. Moroz, S. Yu. Orlov, V. N. Panteleev, Yu. M. Volkov, C. Lau, O. Bajeat, S. Essabaa, P. Jardin, R. Leroy, and L. Stroe
Published 21 July 2006 (4 pages)
017308  Full Text: PDF (95 kB)  | Buy Article
+
Show Abstract
The branching of the 2+-->0+ transition in 92Sr has been measured to 0.032(4) per 92Rb decay. It confirms an earlier measurement which was discarded in nuclear data evaluations because of a contradiction with accepted lower log ft limits. The conflict could be solved assuming that close to half of the decay intensity, mostly as high-energy ground-state transitions, is missing in the decay scheme.

New results for the intensity of bimodal fission in barium channels of the spontaneous fission of 252Cf
C. Goodin, D. Fong, J. K. Hwang, A. V. Ramayya, J. H. Hamilton, K. Li, Y. X. Luo, J. O. Rasmussen, S. C. Wu, M. A. Stoyer, T. N. Ginter, S. J. Zhu, R. Donangelo, G. M. Ter-Akopian, A. V. Daniel, G. S. Popeko, A. M. Rodin, and A. S. Fomichev
Published 21 July 2006 (4 pages)
017309  Full Text: PDF (121 kB)  | Buy Article
+
Show Abstract
Triple coincidence data from the fission of 252Cf were used to deduce the intensity of the proposed "hot" mode in barium channels. gamma-gamma-gamma and alpha-gamma-gamma fission data were analyzed to find the neutron multiplicity distribution for several binary and ternary charge splits. The binary channels Xe-Ru and Ba-Mo were analyzed, as well as the Ba-alpha-Zr, Mo-alpha-Xe, and Te-alpha-Ru ternary channels. An improved method of analysis was used to avoid many of the complexities associated with fission spectra. With this method, we were unable to confirm the second mode in the either the Ba-Mo or Ba-alpha-Zr splits.

Deformation parameter for diffuse density
K. Hagino, N. W. Lwin, and M. Yamagami
Published 27 July 2006 (4 pages)
017310  Full Text: PDF (108 kB)  | Buy Article
+
Show Abstract
In extracting deformation parameters from multipole moments for deformed nuclei, one commonly uses the formulas which are based on a sharp-cut density distribution. We discuss a possible ambiguity for this procedure and clarify the role of diffuseness parameter of the density distribution. For this purpose, we use a deformed Woods-Saxon density as well as a density distribution obtained from the self-consistent relativistic mean-field (RMF) model. We show that the formula using a root-mean-square radius instead of a sharp-cut radius requires a large correction due to a finite surface diffuseness parameter even for stable nuclei. An implication to neutron-rich nuclei is also discussed.

Angular momentum dependence of giant dipole resonance width and Kusnezov parametrization
D. R. Chakrabarty
Published 27 July 2006 (4 pages)
017601  Full Text: PDF (116 kB)  | Buy Article
+
Show Abstract
The angular momentum dependence of the giant dipole resonance width, reported in the literature for nuclei in different mass regions, was compared with a recent comprehensive calculation under the thermal shape fluctuation model. The proper values of the angular momenta to be used in these comparisons are shown to be less than the ones quoted in the literature. There is a disagreement of the experimental results with the model prediction for some nuclei at high spins.

Pionic color transparency
Arnold Larson, Gerald A. Miller, and M. Strikman
Published 28 July 2006 (4 pages)
018201  Full Text: PDF (104 kB)  | Buy Article
+
Show Abstract
We use a semiclassical approximation to investigate the effects of color transparency on pion electroproduction reactions. The resulting reduced nuclear interactions produce significant, but not dominating, differences with the results of conventional distorted-wave, Glauber-type treatments at kinematics accessible to Jefferson Laboratory. Nuclear effects that could mimic the influence of color transparency are also discussed.

COMMENTS

Comment on "187Re(gamma,n) cross section close to and above the neutron threshold"
Thomas Rauscher
Published 13 July 2006 (2 pages)
019801  Full Text: PDF (121 kB)  | Buy Article
+
Show Abstract
The work of Müller et al. [Phys. Rev. C 73, 025804 (2006)] provides interesting experimental data on neutron emission by photodisintegration of 187Re. However, the comparison to theory and the discussed implications for the Re/Os clock require considerable amendment.