- Measurement of the Differential Cross Section for the Reaction γn→π^{-} p from Deuterium
Author(s): W. Chen et al. The CLAS Collaboration
We report a measurement of the differential cross section for the γn→π^{-} p process from the CLAS detector at Jefferson Laboratory in Hall B for photon energies between 1.0 and 3.5 GeV and pion center-of-mass (c.m.) angles (θ_{c.m.} ) between 50° and 115°. We confirm a previous indication of a broad enhancement around a c.m. energy ( sqrt[s] ) of 2.1 GeV at θ_{c.m.} =90° in the scaled differential cross section s^{7} dσ/dt and a rapid falloff in a center-of-mass energy region of about 400 MeV following the enhancement. Our data show an angular dependence of this enhancement as the suggested scaling region is approached for θ_{c.m.} from 70° to 105°.
[Phys. Rev. Lett. 103, 012301] Published Wed Jul 01, 2009
- Isospin Mixing in Nuclei within the Nuclear Density Functional Theory
Author(s): W. Satuła, J. Dobaczewski, W. Nazarewicz, and M. Rafalski
We present the self-consistent, nonperturbative analysis of isospin mixing using the nuclear density functional approach and the rediagonalization of the Coulomb interaction in the good-isospin basis. The unphysical isospin violation on the mean-field level, caused by the neutron excess, is eliminated by the proposed method. We find a significant dependence of the magnitude of isospin breaking on the parametrization of the nuclear interaction. A rough correlation has been found between the isospin-mixing parameter and the difference of proton and neutron rms radii.
[Phys. Rev. Lett. 103, 012502] Published Wed Jul 01, 2009
- Gamow-Teller Strength Distributions in ^{48} Sc by the ^{48} Ca(p,n) and ^{48} Ti(n,p) Reactions and Two-Neutrino Double-β Decay Nuclear Matrix Elements
Author(s): K. Yako et al.
The double-differential cross sections for the ^{48} Ca(p,n) and ^{48} Ti(n,p) reactions were measured at 300 MeV. A multipole decomposition technique was applied to the spectra to extract the Gamow-Teller (GT) components. The integrated GT strengths up to an excitation energy of 30 MeV in ^{48} Sc are 15.3±2.2 and 2.8±0.3 in the (p,n) and (n,p) spectra, respectively. In the (n,p) spectra additional GT strengths were found above 8 MeV where shell models within the fp shell-model space predict almost no GT strengths, suggesting that the present shell-model description of the nuclear matrix element of the two-neutrino double-β decay is incomplete.
[Phys. Rev. Lett. 103, 012503] Published Wed Jul 01, 2009
- Shape Coexistence Near Neutron Number N=20: First Identification of the E0 Decay from the Deformed First Excited J^{π} =0^{+} State in ^{30} Mg
Author(s): W. Schwerdtfeger, P. G. Thirolf, K. Wimmer, D. Habs, H. Mach, T. R. Rodriguez, V. Bildstein, J. L. Egido, L. M. Fraile, R. Gernhäuser, R. Hertenberger, K. Heyde, P. Hoff, H. Hübel, U. Köster, T. Kröll, R. Krücken, R. Lutter, T. Morgan, and P. Ring
The 1789 keV state in ^{30} Mg was identified as the first excited 0^{+} state via its electric monopole (E0) transition to the ground state. The measured small value of ρ^{2} (E0,0_{2}^{+} →0_{1}^{+} )=(26.2±7.5)×10^{-3} implies within a two-level model a small mixing of competing configurations with largely different intrinsic quadrupole deformation near the neutron shell closure at N=20. Axially symmetric configuration mixing calculations identify the ground state of ^{30} Mg to be based on neutron configurations below the N=20 shell closure, while the excited 0^{+} state mainly consists of two neutrons excited into the ν 1f_{7/2} orbital. The experimental result represents the first case where an E0 back decay from a strongly deformed second to the normal deformed first nuclear potential minimum well has been unambiguously identified, thus directly proving shape coexistence at the borderline of the much-debated “island of inversion.”
[Phys. Rev. Lett. 103, 012501] Published Tue Jun 30, 2009
- Mass Ejection by Strange Star Mergers and Observational Implications
Author(s): A. Bauswein, H.-T. Janka, R. Oechslin, G. Pagliara, I. Sagert, J. Schaffner-Bielich, M. M. Hohle, and R. Neuhäuser
We determine the Galactic production rate of strangelets as a canonical input to calculations of the measurable cosmic ray flux of strangelets by performing simulations of strange star mergers and combining the results with recent estimates of stellar binary populations. We find that the flux depends sensitively on the bag constant of the MIT bag model of QCD and disappears for high values of the bag constant and thus more compact strange stars. In the latter case, strange stars could coexist with ordinary neutron stars as they are not converted by the capture of cosmic ray strangelets. An unambiguous detection of an ordinary neutron star would then not rule out the strange matter hypothesis.
[Phys. Rev. Lett. 103, 011101] Published Mon Jun 29, 2009
- Isovector EMC Effect and the NuTeV Anomaly
Author(s): I. C. Cloët, W. Bentz, and A. W. Thomas
A neutron or proton excess in nuclei leads to an isovector-vector mean field which, through its coupling to the quarks in a bound nucleon, implies a shift in the quark distributions with respect to the Bjorken scaling variable. We show that this result leads to an additional correction to the NuTeV measurement of sin^{2} θ_{W} . The sign of this correction is largely model independent and acts to reduce their result. Explicit calculation in nuclear matter within a covariant and confining Nambu–Jona-Lasinio model predicts that this vector field correction may account for a substantial fraction of the NuTeV anomaly. We are therefore led to offer a new interpretation of the NuTeV measurement, namely, that it provides further evidence for the medium modification of the bound nucleon wave function.
[Phys. Rev. Lett. 102, 252301] Published Fri Jun 26, 2009
- Quenching of the SnSbTe Cycle in the rp Process
Author(s): V.-V. Elomaa, G. K. Vorobjev, A. Kankainen, L. Batist, S. Eliseev, T. Eronen, J. Hakala, A. Jokinen, I. D. Moore, Yu. N. Novikov, H. Penttilä, A. Popov, S. Rahaman, J. Rissanen, A. Saastamoinen, H. Schatz, D. M. Seliverstov, C. Weber, and J. Äystö
The nuclides ^{104–108} Sn, ^{106–110} Sb, ^{108,109} Te, and ^{111} I at the expected endpoint of the astrophysical rp process have been produced in ^{58} Ni+ ^{nat} Ni fusion-evaporation reactions at IGISOL and their mass values were precisely measured with the JYFLTRAP Penning trap mass spectrometer. For ^{106} Sb, ^{108} Sb, and ^{110} Sb these are the first direct experimental mass results obtained. The related one-proton separation energies have been derived and the value for ^{106} Sb, S_{p} =424(8) keV, shows that the branching into the closed SnSbTe cycle in the astrophysical rp process is weaker than expected.
[Phys. Rev. Lett. 102, 252501] Published Thu Jun 25, 2009
- Implications of Heavy-Quark Spin Symmetry on Heavy-Meson Hadronic Molecules
Author(s): Feng-Kun Guo, Christoph Hanhart, and Ulf-G. Meißner
In recent years, many heavy mesons and charmonia were observed which do not fit in the conventional quark model expectations. Some of them are proposed to be hadronic molecules. Here we investigate the consequences of heavy-quark spin symmetry on these heavy-meson hadronic molecules. Heavy-quark spin symmetry enables us to predict new heavy-meson molecules and provides us with a method to test heavy-meson molecule assumptions of some newly observed states. In particular, we predict an η_{c}^{′} f_{0} (980) bound state as the spin-doublet partner of the Y(4660) proposed as a ψ^{′} f_{0} (980) bound state with a mass of 4616_{-6}^{+5} MeV and the prominent decay mode η_{c}^{′} ππ. The width is predicted to be Γ(η_{c}^{′} ππ)=60±30 MeV. The π^{+} π^{-} invariant mass spectrum and the line shape are calculated. We suggest searching for this state in B^{±} →η_{c}^{′} K^{±} π^{+} π^{-} , whose branching fraction is expected to be large.
[Phys. Rev. Lett. 102, 242004] Published Fri Jun 19, 2009
- Lifetime Measurements of the Neutron-Rich N=30 Isotones ^{50} Ca and ^{51} Sc: Orbital Dependence of Effective Charges in the fp Shell
Author(s): J. J. Valiente-Dobón et al.
The lifetimes of the first excited states of the N=30 isotones ^{50} Ca and ^{51} Sc have been determined using the Recoil Distance Doppler Shift method in combination with the CLARA-PRISMA spectrometers. This is the first time such a method is applied to measure lifetimes of neutron-rich nuclei populated via a multinucleon transfer reaction. This extends the lifetime knowledge beyond the f_{7/2} shell closure and allows us to derive the effective proton and neutron charges in the fp shell near the doubly magic nucleus ^{48} Ca, using large-scale, shell-model calculations. These results indicate an orbital dependence of the core polarization along the fp shell.
[Phys. Rev. Lett. 102, 242502] Published Tue Jun 16, 2009
- First Gogny-Hartree-Fock-Bogoliubov Nuclear Mass Model
Author(s): S. Goriely, S. Hilaire, M. Girod, and S. Péru
We present the first Gogny-Hartree-Fock-Bogoliubov (HFB) model which reproduces nuclear masses with an accuracy comparable with the best mass formulas. In contrast with the Skyrme-HFB nuclear-mass models, an explicit and self-consistent account of all the quadrupole correlation energies are included within the 5D collective Hamiltonian approach. The final rms deviation with respect to the 2149 measured masses is 798 keV. In addition, the new Gogny force is shown to predict nuclear and neutron matter properties in agreement with microscopic calculations based on realistic two- and three-body forces.
[Phys. Rev. Lett. 102, 242501] Published Mon Jun 15, 2009
- Stellar and Primordial Nucleosynthesis of ^{7} Be: Measurement of ^{3} He(α,γ) ^{7} Be
Author(s): A. Di Leva, L. Gialanella, R. Kunz, D. Rogalla, D. Schürmann, F. Strieder, M. De Cesare, N. De Cesare, A. D’Onofrio, Z. Fülöp, G. Gyürky, G. Imbriani, G. Mangano, A. Ordine, V. Roca, C. Rolfs, M. Romano, E. Somorjai, and F. Terrasi
The ^{3} He(α,γ) ^{7} Be reaction presently represents the largest nuclear uncertainty in the predicted solar neutrino flux and has important implications on the big bang nucleosynthesis, i.e., the production of primordial ^{7} Li. We present here the results of an experiment using the recoil separator ERNA (European Recoil separator for Nuclear Astrophysics) to detect directly the ^{7} Be ejectiles. In addition, off-beam activation and coincidence γ-ray measurements were performed at selected energies. At energies above 1 MeV a large discrepancy compared to previous results is observed both in the absolute value and in the energy dependence of the cross section. Based on the available data and models, a robust estimate of the cross section at the astrophysical relevant energies is proposed.
[Phys. Rev. Lett. 102, 232502] Published Fri Jun 12, 2009
- Multiply Charged Thorium Crystals for Nuclear Laser Spectroscopy
Author(s): C. J. Campbell, A. V. Steele, L. R. Churchill, M. V. DePalatis, D. E. Naylor, D. N. Matsukevich, A. Kuzmich, and M. S. Chapman
We have produced laser-cooled crystals of ^{232} Th ^{3+} in a linear rf Paul trap. This is the first time that a multiply charged ion has been laser cooled. Our work opens an avenue for excitation of the nuclear transition in a trapped, cold ^{229} Th ^{3+} ion. Laser excitation of nuclear states would establish a new bridge between atomic and nuclear physics, with the promise of new levels of metrological precision.
[Phys. Rev. Lett. 102, 233004] Published Fri Jun 12, 2009
- Mechanisms in Knockout Reactions
Author(s): D. Bazin, R. J. Charity, R. T. de Souza, M. A. Famiano, A. Gade, V. Henzl, D. Henzlova, S. Hudan, J. Lee, S. Lukyanov, W. G. Lynch, S. McDaniel, M. Mocko, A. Obertelli, A. M. Rogers, L. G. Sobotka, J. R. Terry, J. A. Tostevin, M. B. Tsang, and M. S. Wallace
We report the first detailed study of the relative importance of the stripping and diffraction mechanisms involved in nucleon knockout reactions, by the use of a coincidence measurement of the residue and fast proton following one-proton knockout reactions. The measurements used the S800 spectrograph in combination with the HiRA detector array at the NSCL. Results for the reactions ^{9} Be( ^{9} C, ^{8} B+X)Y and ^{9} Be( ^{8} B, ^{7} Be+X)Y are presented and compared with theoretical predictions for the two reaction mechanisms calculated using the eikonal model. The data show a clear distinction between the stripping and diffraction mechanisms and the measured relative proportions are very well reproduced by the reaction theory. This agreement adds support to the results of knockout reaction analyses and their applications to the spectroscopy of rare isotopes.
[Phys. Rev. Lett. 102, 232501] Published Thu Jun 11, 2009
- Diffuse Neutrino Flux from Failed Supernovae
Author(s): Cecilia Lunardini
I study the diffuse flux of electron antineutrinos from stellar collapses with direct black hole formation (failed supernovae). This flux is more energetic than that from successful supernovae, and therefore it might contribute substantially to the total diffuse flux above realistic detection thresholds. The total flux might be considerably higher than previously thought, and approach the sensitivity of Super-Kamiokande. For more conservative values of the parameters, the flux from failed supernovae dominates for antineutrino energies above 30–45 MeV, with potential to give an observable spectral distortion at megaton detectors.
[Phys. Rev. Lett. 102, 231101] Published Wed Jun 10, 2009
- Soft Open Charm Production in Heavy-Ion Collisions
Author(s): V. Topor Pop, J. Barrette, and M. Gyulassy
The effects of strong longitudinal color electric fields on the open charm production in nucleus-nucleus (A+A) collisions at 200A GeV are investigated within the framework of the HIJING/BB [over ¯] v2.0 model. A threefold increase of the effective string tension due to in-medium effects in A+A collisions results in a sizable (≈60%–70%) enhancement of the total charm production cross sections (σ_{cc [over ¯] }^{NN} ). The nuclear modification factor shows a suppression at moderate transverse momentum (p_{T} ) consistent with BNL Relativistic Heavy Ion Collider data. At Large Hadron Collider energies the model predicts an increase of σ_{cc [over ¯] }^{NN} by approximately an order of magnitude.
[Phys. Rev. Lett. 102, 232302] Published Tue Jun 09, 2009
- Resolving the Hanbury Brown–Twiss Puzzle in Relativistic Heavy Ion Collisions
Author(s): Scott Pratt
Two particle correlation data from the BNL Relativistic Heavy Ion Collider have provided detailed femtoscopic information describing pion emission. In contrast with the success of hydrodynamics in reproducing other classes of observables, these data had avoided description with hydrodynamic-based approaches. This failure has inspired the term “HBT puzzle,” where HBT refers to femtoscopic studies which were originally based on Hanbury Brown–Twiss interferometry. Here, the puzzle is shown to originate not from a single shortcoming of hydrodynamic models, but the combination of several effects: mainly prethermalized acceleration, using a stiffer equation of state, and adding viscosity.
[Phys. Rev. Lett. 102, 232301] Published Mon Jun 08, 2009
- First Results on Angular Distributions of Thermal Dileptons in Nuclear Collisions
Author(s): R. Arnaldi et al. NA60 Collaboration
The NA60 experiment at the CERN Super Proton Synchrotron has studied dimuon production in 158A GeV In-In collisions. The strong excess of pairs above the known sources found in the complete mass region 0.2[Phys. Rev. Lett. 102, 222301] Published Fri Jun 05, 2009
- Laser Spectroscopy of Niobium Fission Fragments: First Use of Optical Pumping in an Ion Beam Cooler Buncher
Author(s): B. Cheal, K. Baczynska, J. Billowes, P. Campbell, F. C. Charlwood, T. Eronen, D. H. Forest, A. Jokinen, T. Kessler, I. D. Moore, M. Reponen, S. Rothe, M. Rüffer, A. Saastamoinen, G. Tungate, and J. Äystö
A new method of optical pumping in an ion beam cooler buncher has been developed to selectively enhance ionic metastable state populations. The technique permits the study of elements previously inaccessible to laser spectroscopy and has been applied here to the study of Nb. Model independent mean-square charge radii and nuclear moments have been studied for ^{90,90 m,91,91 m,92,93,99,101,103} Nb to cover the region of the N=50 shell closure and N≈60 sudden onset of deformation. The increase in mean-square charge radius is observed to be less than that for Y, with a substantial degree of β softness observed before and after N=60.
[Phys. Rev. Lett. 102, 222501] Published Fri Jun 05, 2009
- γ-Ray Spectroscopy at the Limits: First Observation of Rotational Bands in ^{255} Lr
Author(s): S. Ketelhut et al.
The rotational band structure of ^{255} Lr has been investigated using advanced in-beam γ-ray spectroscopic techniques. To date, ^{255} Lr is the heaviest nucleus to be studied in this manner. One rotational band has been unambiguously observed and strong evidence for a second rotational structure was found. The structures are tentatively assigned to be based on the 1/2^{-} [521] and 7/2^{-} [514] Nilsson states, consistent with assignments from recently obtained α decay data. The experimental rotational band dynamic moment of inertia is used to test self-consistent mean-field calculations using the Skyrme SLy4 interaction and a density-dependent pairing force.
[Phys. Rev. Lett. 102, 212501] Published Fri May 29, 2009
- Masses of ^{130} Te and ^{130} Xe and Double-β-Decay Q Value of ^{130} Te
Author(s): Matthew Redshaw, Brianna J. Mount, Edmund G. Myers, and Frank T. Avignone
The atomic masses of ^{130} Te and ^{130} Xe have been obtained by measuring cyclotron frequency ratios of pairs of triply charged ions simultaneously trapped in a Penning trap. The results, with 1 standard deviation uncertainty, are M( ^{130} Te)=129.906 222 744(16) u and M( ^{130} Xe)=129.903 509 351(15) u. From the mass difference the double-β-decay Q value of ^{130} Te is determined to be Q_{ββ} ( ^{130} Te)=2527.518(13) keV. This is a factor of 150 more precise than the result of the AME2003 [G. Audi , Nucl. Phys. A729, 337 (2003)].
[Phys. Rev. Lett. 102, 212502] Published Fri May 29, 2009
- Comment on “Mass and KΛ Coupling of the N^{*} (1535)”
Author(s): S. Ceci, A. Švarc, and B. Zauner
A Comment on the Letter by B. C. Liu and B. S. Zou, Phys. Rev. Lett. 96, 042002 (2006).
[Phys. Rev. Lett. 102, 209101] Published Fri May 22, 2009
- Towards a Unified Understanding of Jet Quenching and Elliptic Flow within a Perturbative QCD Parton Transport
Author(s): Oliver Fochler, Zhe Xu, and Carsten Greiner
The gluonic contribution to the nuclear modification factor R_{AA} is investigated for central Au+Au collisions at sqrt[s] =200 AGeV employing a perturbative QCD-based parton cascade including radiative processes. A flat quenching pattern is found up to transverse momenta of 30 GeV, which is slightly smaller compared with results from the Gyulassy-Levai-Vitev formalism. We demonstrate that the present microscopic transport description provides a challenging means of investigating both jet quenching and a strong buildup of elliptic flow in terms of the same standard perturbative QCD interactions.
[Phys. Rev. Lett. 102, 202301] Published Wed May 20, 2009
- Probing Neutron Correlations through Nuclear Breakup
Author(s): Marlène Assié and Denis Lacroix
The effect of initial correlations between nucleons on the nuclear breakup mechanism is studied. A quantum transport theory which extends the standard mean-field approach is developed to incorporate short range pairing correlation as well as direct nucleon-nucleon collisions. A time evolution of the nuclear breakup from a correlated system leading to the emission of two particles to the continuum is performed. We show that initial correlations have strong influence on relative angles between particles emitted in coincidence. The present qualitative study indicates that nuclear breakup might be a tool to infer the residual interaction between nucleons in the nuclear medium.
[Phys. Rev. Lett. 102, 202501] Published Wed May 20, 2009
- Prediction of a Photon Peak in Relativistic Heavy Ion Collisions
Author(s): Jorge Casalderrey-Solana and David Mateos
We show that if a flavorless vector meson remains bound after deconfinement, and if its limiting velocity in the quark-gluon plasma is subluminal, then this meson produces a distinct peak in the spectrum of thermal photons emitted by the plasma. We also demonstrate that this effect is a universal property of all strongly coupled, large-N_{c} plasmas with a gravity dual. For the J/ψ, the corresponding peak lies between 3 and 5 GeV and could be observed in heavy-ion collisions at the LHC.
[Phys. Rev. Lett. 102, 192302] Published Thu May 14, 2009
- Breaking Strain of Neutron Star Crust and Gravitational Waves
Author(s): C. J. Horowitz and Kai Kadau
Mountains on rapidly rotating neutron stars efficiently radiate gravitational waves. The maximum possible size of these mountains depends on the breaking strain of the neutron star crust. With multimillion ion molecular dynamics simulations of Coulomb solids representing the crust, we show that the breaking strain of pure single crystals is very large and that impurities, defects, and grain boundaries only modestly reduce the breaking strain to around 0.1. Because of the collective behavior of the ions during failure found in our simulations, the neutron star crust is likely very strong and can support mountains large enough so that their gravitational wave radiation could limit the spin periods of some stars and might be detectable in large-scale interferometers. Furthermore, our microscopic modeling of neutron star crust material can help analyze mechanisms relevant in magnetar giant flares and microflares.
[Phys. Rev. Lett. 102, 191102] Published Wed May 13, 2009
- Observation of an “ABC” Effect in Proton-Proton Collisions
Author(s): S. Dymov, M. Hartmann, A. Kacharava, A. Khoukaz, V. Komarov, P. Kulessa, A. Kulikov, V. Kurbatov, G. Macharashvili, S. Merzliakov, M. Mielke, S. Mikirtychiants, M. Nekipelov, M. Nioradze, H. Ohm, F. Rathmann, H. Ströher, D. Tsirkov, Yu. Uzikov, Yu. Valdau, C. Wilkin, S. Yaschenko, and B. Zalikhanov
The cross section for inclusive multipion production in the pp→ppX reaction was measured at COSY-ANKE at four beam energies, 0.8, 1.1, 1.4, and 2.0 GeV, for low excitation energy in the final pp system, such that the diproton quasiparticle is in the ^{1} S _{0} state. At the three higher energies, the missing-mass M_{X} spectra show a strong enhancement at low M_{X} , corresponding to an Abashian-Booth-Crowe effect that moves steadily to larger values as the energy is increased. Despite the missing-mass structure looking very different at 0.8 GeV, the variation with M_{X} and beam energy are consistent with two-pion production being mediated through the excitation of two Δ(1232) isobars, coupled to S and D states of the initial pp system. There is no sign of any resonancelike structure in the energy dependence of the type recently observed for the pn→dπ^{0} π^{0} total cross section.
[Phys. Rev. Lett. 102, 192301] Published Wed May 13, 2009
- Fission Barriers of Compound Superheavy Nuclei
Author(s): J. C. Pei, W. Nazarewicz, J. A. Sheikh, and A. K. Kerman
The dependence of fission barriers on the excitation energy of the compound nucleus impacts the survival probability of superheavy nuclei synthesized in heavy-ion fusion reactions. In this work, we investigate the isentropic fission barriers by means of the self-consistent nuclear density functional theory. The relationship between isothermal and isentropic descriptions is demonstrated. Calculations have been carried out for ^{264} Fm, ^{272} Ds, ^{278} 112, ^{292} 114, and ^{312} 124. For nuclei around ^{278} 112 produced in “cold-fusion” reactions, we predict a more rapid decrease of fission barriers with excitation energy as compared to the nuclei around ^{292} 114 synthesized in “hot-fusion” experiments. This is explained in terms of the difference between the ground-state and saddle-point temperatures. The effect of the particle gas is found to be negligible in the range of temperatures studied.
[Phys. Rev. Lett. 102, 192501] Published Wed May 13, 2009
- Precise Measurement of the Neutron Magnetic Form Factor G_{M}^{n} in the Few-GeV^{2} Region
Author(s): J. Lachniet et al. CLAS Collaboration
The neutron elastic magnetic form factor was extracted from quasielastic electron scattering on deuterium over the range Q^{2} =1.0–4.8 GeV^{2} with the CLAS detector at Jefferson Lab. High precision was achieved with a ratio technique and a simultaneous in situ calibration of the neutron detection efficiency. Neutrons were detected with electromagnetic calorimeters and time-of-flight scintillators at two beam energies. The dipole parametrization gives a good description of the data.
[Phys. Rev. Lett. 102, 192001] Published Tue May 12, 2009
- Random matrices and chaos in nuclear physics: Nuclear structure
Author(s): H. A. Weidenmüller and G. E. Mitchell
Evidence for the applicability of random-matrix theory to nuclear spectra is reviewed. In analogy to systems with few degrees of freedom, one speaks of chaos (more accurately, quantum chaos) in nuclei whenever random-matrix predictions are fulfilled. An introduction into the basic concepts of random-matrix theory is followed by a survey over the extant experimental information on spectral fluctuations, including a discussion of the violation of a symmetry or invariance property. Chaos in nuclear models is discussed for the spherical shell model, for the deformed shell model, and for the interacting boson model. Evidence for chaos also comes from random-matrix ensembles patterned after the shell model such as the embedded two-body ensemble, the two-body random ensemble, and the constrained ensembles. All this evidence points to the fact that chaos is a generic property of nuclear spectra, except for the ground-state regions of strongly deformed nuclei.
[Rev. Mod. Phys. 81, 539] Published Fri May 08, 2009
- In-Beam γ-Ray Spectroscopy of Very Neutron-Rich Nuclei: Excited States in ^{46} S and ^{48} Ar
Author(s): A. Gade, P. Adrich, D. Bazin, B. A. Brown, J. M. Cook, C. Aa. Diget, T. Glasmacher, S. McDaniel, A. Ratkiewicz, K. Siwek, and D. Weisshaar
We report on the first in-beam γ-ray spectroscopy study of the very neutron-rich nucleus ^{46} S. The N=30 isotones ^{46} S and ^{48} Ar were produced in a novel way in two steps that both necessarily involve nucleon exchange and neutron pickup reactions ^{9} Be( ^{48} Ca, ^{48} K)X followed by ^{9} Be( ^{48} K, ^{48} Ar+γ)X at 85.7 MeV/u midtarget energy and ^{9} Be( ^{48} Ca, ^{46} Cl)X followed by ^{9} Be( ^{46} Cl, ^{46} S+γ)X at 87.0 MeV/u midtarget energy, respectively. The results are compared to large-scale shell-model calculations in the sd-pf shell using the SDPF-NR effective interaction and Z-dependent modifications.
[Phys. Rev. Lett. 102, 182502] Published Thu May 07, 2009
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