39044560
Neutron halos in the Na isotopes.
The neutron and proton density distributions of the Na isotopes out to the proton and neutron drip lines are calculated in the spherical Hartree-Fock model with a wide variety of density-dependent Skyrme interactions. The results are compared to recent experimental data for the interaction cross sections and for the rms radii. We discuss the role of the deformed intruder states and the problems associated with predicting the location of the neutron drip line for this mass region. {copyright} {ital 1996 The American Physical Society.}
35774621
Many-body approximations in the sd-shell "sandbox"
A new theoretical approach is presented that combines the Hartree-Fock variational scheme with the exact solution of the pairing problem in the finite orbital space. Using this formulation in the sd-space as an example, we show that the exact pairing significantly improves the results for the ground state energy.
10644949
One-neutron knockout reactions on proton-rich nuclei with N = 16
One-neutron knockout reactions from the deeply bound N=16 isotones with Z=16,17, and 18 have been studied in inverse kinematics with intermediate-energy beams. gamma-ray spectroscopy in coincidence with the detection of knockout residues allowed for an investigation of the one-neutron removal leading to individual excited states. Spectroscopic factors are deduced in the framework of the sudden and eikonal approximations and are compared to USD shell-model predictions. The momentum distributions observed in the experiment are used to identify the angular momentum l carried by the knockedout neutron by comparing with calculations based on a black-disk reaction model. The systematics of reduced single-particle occupancies attributed to the effect of short-range correlations, observed so far for stable and near-magic nuclei in (e,e(')p) and (d,He-3) reactions and in one-nucleon knockout on light deeply bound systems, are extended in this work.
41679008
Proton capture to excited states of O 16 : M 1 , E 1 , and Gamow-Teller transitions and shell model calculations
We have measured excitation functions of the ..gamma..-rays resulting from the bombardment of /sup 15/N by polarized and unpolarized protons in the energy range E/sub p/ = 2.5 to 9.5 MeV with emphasis on identifying dipole decays to the first (0/sup +/) and second (3/sup -/) excited states in /sup 16/O. Resonances in ..gamma../sub 12/ are observed at E/sub x/ = 16.21, 16.45, 16.82, 17.12, 18.03, 18.98, 19.90 and 20.41 MeV. The 16.21 and 17.12 MeV resonances in ..gamma../sub 12/ are identified as M1-decays of the 1/sup +/ T = 1 states to the 6.05 MeV 0/sup +/ state in /sup 16/O. The measured ratio of reduced strengths B(m1,..gamma../sub 1/)/(B(M1,..gamma../sub 0/) is 0.48 +- 0.03 for decays from the 16.21 MeV state and 0.55 +- 0.04 for decays from the 17.12 MeV state. The 18.03 MeV resonance is due to a 3/sup -/ T = 1 state in /sup 16/O with a strength Gamma/sup p/Gamma/sub gamma 2//Gamma = (1.96 +- 0.27) eV and the 18.98 MeV resonance is due to the 4/sup -/ T = 1 stretched particle-hole state with a strength of (0.85 +- 0.10) eV. We determine absolute particle and ..gamma.. widths for these states. The M1 ..gamma../submore » 2/-width of the 18.98 MeV state, (7.1 +- 3.1) eV, is in agreement with a shell-model calculation. Resonances in ..gamma../sub 3/ are observed at 16.82 and 17.27 MeV and in ..gamma../sub 4/ at 17.88 MeV. The excitation energies and widths of these levels as well as the strengths of the ..gamma.. transitions suggest T = 1 character for all of the resonances for which capture ..gamma..-rays are observed. Correspondences of our resonances to levels in /sup 16/N are given. We compare ..gamma.. widths, including ground-state M1 decays, and allowed ..beta.. transition rate in A = 16 nuclei with shell model calculations and obtain rough agreement. Additional shell model calculations for M1 and GT (Gamow-Teller) decays in the A-14, 15, 17 and 18 nuclei are presented, which indicate that GT matrix elements are quenched by approx. 20% relative to shell model predictions and also relative to the spin part of the M1 matrix elements.« less
120853289
The 52,54Cr(p, n)52,54Mn and 57,58Fe(p, n)57,58Co reactions at Ep = 120 MeV
Abstract Differential cross sections for the (p, n) reaction on 52, 54 Cr and 57, 58 Fe have been measured for angles up to θ lab = 10.5° and 14.6°, respectively, using 120 MeV protons. The observed angular distributions are used to evaluate the location and strength of Gamow-Teller resonances. A shell-model calculation of this strength distribution is presented and compared with the experimental results. The M1 strength for 52 Cr is also calculated and compared with available results from (e, e') and (p, p') experiments. A comparison is made with other If 7 2 nuclei.
39136906
Structure of C-16: Testing shell model and ab initio approaches
Excited states in C-16 were populated via the Be-9(N-17,C-16+gamma)X one-proton knockout reaction. The lifetime of the 2(1)(+) state in C-16 was measured using the recoil distance method. The extracted lifetime of tau(+)(21) = 11.4(-0.9)(+0.8)(stat) +/- 0.7(syst(B rho))(-1.5)(+0.0)(syst(feeding)) ps yields a deduced B(E2;2(1)(+) -> 0(1)(+)) = 4.21(-0.26)(+0.34)(stat)(-0.24)(+0.28)(syst(B rho))(-0.00)(+0.64)(syst(feeding)) e(2)fm(4) value in good agreement with a previous measurement. The one-proton knockout cross section is used to extract the proton amplitude of the C-16 2(1)(+) state, which confirms the neutron dominant character of this state. Gamma-ray branching ratios between the 2(2)(+) state and the 2(1)(+) and ground states were also determined. The results are compared with p-sd shell model and no-core shell model (with NN and NN + NNN) calculations. The inclusion of three-body forces are essential in order for the no-core shell model calculations to reproduce the experimental findings on the gamma-ray branching ratios.
28894226
Proton-nucleus scattering and density dependent meson masses in the nucleus.
The influence of density dependent meson masses, proposed in many previous papers, on proton-nucleus scattering in the several hundred MeV region is investigated. Introduction of this density dependence is found to remove the nuclear radius discrepancy which persistently occurred in analyses with the nonrelativistic impulse approximation when empirical nuclear densities obtained from electron scattering were employed. Nonlocality, suggested by earlier derivations of the density dependent masses, had to be introduced. Taking the estimated range of nonlocality from the earlier calculations, agreement with experiment was significantly improved by this introduction. Effects on the spin-orbit interaction and imaginary part of the optical model are qualitatively discussed. The density dependent meson masses aid in increasing the strength of the spin-orbit interaction. Preliminary results calculated in a relativistic impulse approximation (IA2) formalism for the spin observables are shown and discussed.
668564
Medium effects on kaon and antikaon spectra in heavy-ion collisions.
In the linear chiral perturbation theory, both kaon and antikaon masses decrease in dense matter. There is also a repulsive vector potential for the kaon and an attractive one for the antikaon. With these effects included in the relativistic transport model, it is found that the slope parameter of the kaon kinetic energy distribution is larger than that of the antikaon. This is consistent with the experimental data from heavy-ion collisions in the Alternating Gradient Synchrotron experiments at Brookhaven.
13068301
Temperature, energy, and heat capacity of asymptotically anti-de Sitter black holes.
We investigate the thermodynamical properties of black holes in (3+1)- and (2+1)-dimensional Einstein gravity with a negative cosmological constant. In each case, ther thermodynamic internal energy is computed for a finite spatial region that contains the black hole. The temperature at the boundary of this regoin is defined by differentiating the energy with respect to entropy, and is equal to the product of the surface gravity (divided by 2\ensuremath{\pi}) and the Tolman redshift factor for temperature in a stationary gravitational field. We also compute the thermodynamic surface pressure and, in the case of the 2+1 black hole, show that the chemical potential conjugate to angular momentum is equal to the proper angular velocity of the black hole with respect to observers who are at rest in the stationary time slices. In 3+1 dimensions, a calculation of the heat capacity reveals the existence of a thermodynamically stable black hole solution and a negative heat capacity instanton. This result holds in the limit that the spatial boundary tends to infinity only if the cosmological constant is negative; if the cosmological constant vanishes, the stable black hole solution is lost. In 2+1 dimensions, a calculation of the heat capacity reveals the existence of a thermodynamically stable black hole solution, but no negative heat capacity instanton.
1772289
Temporal development of the plasma phase transition.
We present a simple argument to show why a high entropy phase must exhibit an extended pion source lifetime. The plasmas that would be formed under the conditions of the recent heavy ion experiments would emit pions over a time of the order of 10 fm/{ital c} or longer, if the plasma has an entropy density larger than that of a pion gas by an order of magnitude.
36218377
Spin of the proton and the chiral bag.
Measurement of the spin carried by the quarks in the proton can be very important in distinguishing between low-energy models of the hadron. Topological soliton models have rather little or no spin in the quarks, in agreement with present experimental indications.