arXiv subjects

S. Karataglidis

Publications and source records attributed to S. Karataglidis.

At least 55 records · Page 3Linked to original sources

arXiv2006

Properties of effective interactions and the excitation of 6- states in 28Si

Cross-section and analyzing power data from (p,p') scattering to the 6- states at 11.58 and 14.35 MeV in 28Si, taken with energies of 80, 100, 134, and 180 MeV protons, have been analyzed using a distorted wave approximation with microscopically defined wave functions. The results, taken in conjunction with an analysis of an M6 electron scattering form factor, suggest that the two states exhaust respectively, ~50% and ~60% of the strengths of isoscalar and isovector particle-hole excitations from the ground state. The energy variation of data also suggests that the non-central components of the effective interactions at 80 and 100 MeV may need to be enhanced.

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arXiv2005

Low-energy neutron-12C analyzing powers: Results from a multichannel algebraic scattering theory

Analyzing powers in low-energy neutron scattering from 12C are calculated in an algebraic momentum-space coupled-channel formalism (MCAS). The results are compared with recently obtained experimental data. The channel-coupling potentials have been defined previously to reproduce the total cross section and sub-threshold bound states of the compound system. Without further adjustment, good agreement with data for the analyzing powers is obtained.

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arXiv2005

Comparison between two methods of solution of coupled equations for low-energy scattering

Cross sections from low-energy neutron-nucleus scattering have been evaluated using a coupled channel theory of scattering. Both a coordinate-space and a momentum-space formalism of that coupled-channel theory are considered.A simple rotational model of the channel interaction potentials is used to find results using two relevant codes, ECIS97 and MCAS, so that they may be compared. The very same model is then used in the MCAS approach to quantify the changes that occur when allowance is made for effects of the Pauli principle.

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arXiv2005

Modern optical potentials and the role of nuclear structure

Microscopic descriptions of exotic nuclei are the subject of much experimental and theoretical effort. Not only are such important in their own right but are also necessary for applications in nuclear astrophysics. Evaluations of model wave functions may be done with analyses of elastic and inelastic scattering from hydrogen. Those require a realistic model of nucleon-nucleus scattering as scattering from hydrogen translates to proton scattering in the inverse kinematics. The Melbourne g-folding model for intermediate energy is presented along with various examples. Implications for existing and future experimental and theoretical work are discussed.

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arXiv2005

Predicting narrow states in the spectrum of a nucleus beyond the proton drip line

Properties of particle-unstable nuclei lying beyond the proton drip line can be ascertained by considering those (usually known) properties of its mirror neutron-rich system. We have used a multi-channel algebraic scattering theory to map the known properties of the neutron-${}^{14}$C system to those of the proton-${}^{14}$O one from which we deduce that the particle-unstable ${}^{15}$F will have a spectrum of two low lying broad resonances of positive parity and, at higher excitation, three narrow negative parity ones. A key feature is to use coupling to Pauli-hindered states in the target.

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arXiv2005

Solution of multi-channel problems using MCAS for spectra and scattering cross sections

A multi-channel algebraic scattering theory, to find solutions of coupled-channel scattering problems with interactions determined by collective models, has been structured to ensure that the Pauli principle is not violated. Positive (scattering) and negative (sub-threshold) solutions can be found to predict both the compound nucleus sub-threshold spectrum and all resonances due to coupled-channel effects that occur on a smooth energy varying background. The role of the Pauli principle is crucial in defining what interaction potentials are required to fit data. The theory also gives an algebraic form for the dynamic polarization potential which adds to the ground state interaction to define the optical potential that gives the same elastic scattering cross sections.

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arXiv2005

Low energy nuclear scattering and sub-threshold spectra from a multi-channel algebraic scattering theory

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arXiv2005

Complementary reaction analyses and the isospin mixing of the 4- states in 16O

Data from the inelastic scattering of electrons, and of intermediate energy protons and pions leading to ``stretched'' configuration 4- states near 19 MeV excitation in 16O as well as from charge exchange (p,n) scattering to an isobaric analogue (4-) state in 16F have been analyzed to ascertain the degree of isospin mixing contained within those states and of the amount of d_{5/2}-p_{3/2}^{-1} particle-hole excitation strength they exhaust. The electron and proton scattering data have been analyzed using microscopic models of the structure and reactions, with details constrained by analyses of elastic scattering data.

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arXiv2005

Microscopic description of elastic and inelastic proton scattering from 208Pb

Information on the equation of state (EOS) of neutron matter may be gained from studies of 208Pb. Descriptions of 208Pb require credible models of structure, taking particular note also of the spectrum. Such may be tested by analyses of scattering data. Herein, we report on such analyses using an RPA model for 208Pb in a folding model of the scattering. No a posteriori adjustment of parameters are needed to obtain excellent agreement with data. From those analyses, the skin thickness of 208Pb is constrained to lie in the range 0.13-0.17 fm.

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arXiv2005

Comparison of optical model results from a microscopic Schrödinger approach to nucleon-nucleus elastic scattering with those from a global Dirac phenomenology

Comparisons are made between results of calculations for intermediate energy nucleon-nucleus scattering for 12C, 16O, 40Ca, 90Zr, and 208Pb, using optical potentials obtained from global Dirac phenomenology and from a microscopic Schrödinger model. Differential cross sections and spin observables for scattering from the set of five nuclei at 65 MeV and 200 MeV have been studied to assess the relative merits of each approach. Total reaction cross sections from proton-nucleus and total cross sections from neutron-nucleus scattering have been evaluated and compared with data for those five targets in the energy range 20 MeV to 800 MeV. The methods of analyses give results that compare well with experimental data in those energy regimes for which the procedures are suited.

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arXiv2005

Probing Correlated Ground States with Microscopic Optical Model for Nucleon Scattering off Doubly-Closed-Shell Nuclei

The RPA long range correlations are known to play a significant role in understanding the depletion of single particle-hole states observed in (e, e') and (e, e'p) measurements. Here the Random Phase Approximation (RPA) theory, implemented using the D1S force is considered for the specific purpose of building correlated ground states and related one-body density matrix elements. These may be implemented and tested in a fully microscopic optical model for NA scattering off doubly-closed-shell nuclei. A method is presented to correct for the correlations overcounting inherent to the RPA formalism. One-body density matrix elements in the uncorrelated (i.e. Hartree-Fock) and correlated (i.e. RPA) ground states are then challenged in proton scattering studies based on the Melbourne microscopic optical model to highlight the role played by the RPA correlations. Effects of such correlations which deplete the nuclear matter at small radial distance (r $<$ 2 fm) and enhance its surface region, are getting more and more sizeable as the incident energy increases. Illustrations are given for proton scattering observables measured up to 201 MeV for the $^{16}$O, $^{40}$Ca, $^{48}$Ca and $^{208}$Pb target nuclei. Handling the RPA correlations systematically improves the agreement between scattering predictions and data for energies higher than 150 MeV.

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arXiv2005

Role of the Pauli principle in collective-model coupled-channels calculations

A multi-channel algebraic scattering theory, to find solutions of coupled-channel scattering problems with interactions determined by collective models, has been structured to ensure that the Pauli principle is not violated. By tracking the results in the zero coupling limit, a correct interpretation of the sub-threshold and resonant spectra of the compound system can be made. As an example, the neutron-12C system is studied defining properties of 13C to 10 MeV excitation. Accounting for the Pauli principle in collective coupled-channels models is crucial to the outcome.

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arXiv2005

Compound and quasi-compound states in low-energy scattering of nucleons from 12C

A multi-channel algebraic scattering theory has been used to study the properties of nucleon scattering from 12C and of the sub-threshold compound nuclear states, accounting for properties in the compound nuclei to ~10 MeV. All compound and quasi-compound resonances observed in total cross-section data are matched, and on seeking solutions of the method at negative energies, all sub-threshold states in 13C and 13N are predicted with the correct spin-parities and with reasonable values for their energies. A collective-model prescription has been used to define the initiating nucleon-12C interactions and via use of orthogonalizing pseudo-potentials, account is made of the Pauli principle. Information is extracted on the underlying structure of each state in the compound systems by investigating the zero-deformation limit of the results.

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arXiv2004

Local scale transformations and extended matter distributions in nuclei

Local scale transformations are made to vary the long range properties of harmonic oscillator orbitals conventionally used in model structure calculations of nuclear systems. The transformations ensure that those oscillator states asymptotically have exponentially decaying forms consistent with chosen single nucleon binding energies, leaving the structure essentially unchanged within the body of the nucleus. Application has been made to the radioactive nuclei 6,8He and 11Li and the resulting wave functions are used to generate g-folding optical potentials for elastic scattering of those ions from hydrogen. As a consistency test, application has been made to form wave functions for 40Ca and they have been used also to specify relevant proton-40Ca optical potentials with which elastic scattering has been predicted. The need for appropriate specifications of single particle binding energies in exotic nuclei is discussed.

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arXiv2004

Simple function form for n+208Pb total cross section between 5 and 600 MeV

The total cross section for neutron scattering from 208Pb with energies between 5 and 600 MeV has been analyzed extending a previously defined simple function of three parameters to reveal a Ramsauer-like effect throughout the whole energy range. This effect can be parametrized in a simple way so that it may be anticipated that the complete function prescription will apply for total cross sections from other nuclei.

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arXiv2004

Is friction responsible for the reduction of fusion rates far below the Coulomb barrier?

The fusion of two interacting heavy ions traditionally has been interpreted in terms of the penetration of the projectile into the target. Observed rates well below the Coulomb barrier are considerably lower than estimates obtained from penetration factors. One approach in the analysis of the data invokes coupling to non-elastic channels in the scattering as the source of the depletion. Another is to analyze those data in terms of tunneling in semi-classical models, with the observed depletion being taken as evidence of a ``friction'' under the barrier. A complementary approach is to consider such tunneling in terms of a fully quantal model. We investigate tunneling with both one-dimensional and three-dimensional models in a fully quantal approach to investigate possible sources for such a friction. We find that the observed phenomenon may not be explained by friction. However, we find that under certain conditions tunneling may be enhanced or diminished by up to 50%, which finds analogy with observation, without the invocation of a friction under the barrier.

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arXiv2004

Probing the densities of the Sn isotopes

Proton and neutron densities have been obtained for the even-even isotopes of Sn from $^{100}$Sn to $^{176}$Sn using a Hartree-Fock-Bogoliubov model with a Skyrme interaction. The matter densities so defined have been used with realistic nucleon-nucleon interactions in a folding model to specify optical potentials for the elastic scattering of protons with energies in the range 40 to 200 MeV. Those potentials have been used to make predictions of the differential cross sections and spin observables for proton scattering. As the target mass increases, the emergence of the neutron skin in the Sn isotopes is revealed by marked effects in the differential cross section. Comparisons with available data show how similar scattering data for the neutron-rich isotopes may provide constraints for the model structures.

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arXiv2002

Predictions of total and total reaction cross sections for nucleon-nucleus scattering up to 300 MeV

Total reaction cross sections are predicted for nucleons scattering from various nuclei. Projectile energies to 300 MeV are considered. So also are mass variations of those cross sections at selected energies. All predictions have been obtained from coordinate space optical potentials formed by full folding effective two-nucleon (NN) interactions with one body density matrix elements (OBDME) of the nuclear ground states. Good comparisons with data result when effective NN interactions defined by medium modification of free NN t matrices are used. Coupled with analyses of differential cross sections, these results are sensitive to details of the model ground states used to describe nuclei.

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