lewy róg Logo Instytutu Fizyki UMCS niemożliwe możliwym! Logo Instytutu Fizyki UMCS prawy róg

Strona główna » Instytut » Pracownicy » Andrzej Baran

prof. dr hab. Andrzej Baran

Zakład

Zakład Teorii Jądra Atomu

Stanowisko:

profesor zwyczajny

Kontakt:

pokój: 310
telefon: (081) 537-61-74
e-mail: andrzej.baran@umcs.pl

Specjalność naukowa:

fizyka teoretyczna jadra at.

Publikacje: Ukryj abstrakty

  1. A. Staszczak,M. Stoitsov,A. Baran,W. Nazarewicz, Augmented Lagrangian method for constrained nuclear density functional theory, The European Physical Journal A, 46(), 2010, 85-90

  2. Łojewski, Z. Baran, A., Spontaneous fission half lives of Z=112 isotope, International Journal of Modern Physics E – Nuclear Physics, 17(), 2008, 253-258

  3. Baran, A. Bulgac, A. McNeil Forbes, M. Hagen, G. Nazarewicz, W. Schunck, N. Stoitsov, M., Broyden’s method in nuclear structure calculations, Physical Review C, 78(), 2008, 014318(1-10)

  4. Sieja, K. Ha, T.L. Quentin, P. Baran, A., Particle number conserving approach to correlations, International Journal of Modern Physics E, 16(), 2007, 289-297

  5. Baran, A. Łojewski, Z. Sieja, K., Pairing and α-decay, International Journal of Modern Physics E, 16(), 2007, 320-327

  6. Baran, A. Staszczak, A. Dobaczewski, J. Nazarewicz, W., Collective inertia and fission barriers within the Skyrme-Hartree-Fock theory, International Journal of Modern Physics E, 16(), 2007, 443-451

  7. Sieja, K. Baran, A. Quentin, P., Skyrme force-like extension of the nuclear pairing interaction, Physica Scripta, T125(), 2006, 220-221

    Abstract:
    In this paper, isovector and isoscalar pairing correlations were investigated using generalized Bardeen-Cooper-Shrieffer theory and a Skyrme force-like form of the residual interaction. The calculations are done for even-even N similar to Z germanium nuclei in an axially symmetric Skyrme-Hartree- Fock + BCS scheme with SIII force and time-reversal invariance. A coexistence of T = 0 and T = 1 superfluid phases is observed.

  8. Baran, A. Lojewski, Z. Sieja, K., Superheavy nuclei in different pairing models, International Journal of Modern Physics E-Nuclear Physics, 15(2), 2006, 452-456

    Abstract:
    Pairing plays an important role in both mean-field and macroscopic-microscopic description of the fission process. We discuss two kinds of pairing models: monopole (g = const) and state dependent (delta-type force). As is known the BCS theory leads to the particle number symmetry braking. To restore the symmetry one uses a projection methods (projection before- or after variation) or one solves the Lipkin-Nogami equations. We apply all these methods in the case of monopole pairing. Fission barriers, inertia parameters and spontaneous fission half-lives are studied in the case of Z = 112 isotopes.

  9. Sieja, K. Baran, A., Proton-neutron pairing in Lipkin-Nogami approach, Acta Physica Polonica B, 37(1), 2006, 107-113

    Abstract:
    State-dependent delta-force is used to analyze isovector (T = 1) and isoscalar (T = 0) superfluidity in the framework of the generalized BCS model with an approximate Lipkin-Nogami particle-number projection. Calculations are performed with the single-particle levels generated in axially symmetric Skyrme- Hartree-Fock code with SIII force for several medium-mass N similar to Z nuclei.

  10. Baran, A. Lojewski, Z. Sieja, K., Ground-state properties of superheavy elements in macroscopic- microscopic models, European Physical Journal A, 25(), 2005, 611-612

    Abstract:
    Masses, alpha-decay and spontaneous fission half-lives of superheavy elements are studied in macroscopic-microscopic approaches with two different macroscopic models and the delta- pairing interaction. Model mass deviations obtained with different formulae are 0.5-0.8 MeV.

  11. Baran, A. Lojewski, Z. Sieja, K. Kowal, M., Global properties of even-even superheavy nuclei in macroscopic-microscopic models, Physical Review C, 72(4), 2005, art. no.-044310

    Abstract:
    A systematic study of global properties of superheavy nuclei in the framework of macroscopic-microscopic method is performed. Equilibrium deformations, masses, quadrupole moments, radii, shell energies, fission barriers and half-lives are calculated using the following macroscopic models: Myers-Swiatecki liquid drop, droplet, Yukawa-plus-exponential, and Lublin-Strasbourg drop. Shell and pairing energies are calculated in Woods-Saxon potential with a universal set of parameters. The analysis covers a wide range of even-even superheavy nuclei from Z=100 to 122. Magic and semimagic numbers occurring in this region are indicated and their influence on the observables is discussed. The strongest shell effects appear at proton number Z=114 and at neutron number N=184. Deformed shell closures are found at N=152 and 162. Spontaneous fission half-lives are calculated in a dynamical approach where the full minimization of the action integral in a three-dimensional deformation space of beta deformations is performed. The fission half-lives obtained this way are two orders of magnitude smaller than the ones resulting from static calculations. The agreement of theoretical results and experimental data is satisfying.

  12. Baran, A., Neutron halo in heavy nuclei, Journal of Physics G-Nuclear and Particle Physics, 31(10), 2005, S1823-S1826

    Abstract:
    The halo factor is one of the experimental data which aims to describe a distribution of neutrons in nuclear periphery. In this work we use the relativistic mean field model and calculate the neutron excess factor A B defined in the text. The results of the calculations are compared to the measured data.

  13. Baran, A. Kowal, M. Lojewski, Z. Sieja, K., Properties of superheavy nuclei in various macroscopic- microscopic models, International Journal of Modern Physics E-Nuclear Physics, 14(3), 2005, 365-372

    Abstract:
    In the framework of various macroscopic-microscopic models we examine the ground state properties: separation energies, mean square charge radii, electric quadrupole moments as well as fission barriers, mass parameters, spontaneous fission and alpha decay half-lives of superheavy nuclei. Four macroscopic models and two models of pairing interactions are applied and studied. The approach is based on the deformed Woods-Saxon potential. Spontaneous fission half-lives are calculated within a multi-dimensional dynamical-programming method where the action integral is minimized within the three dimensional space of the nuclear deformation parameters {beta(2), beta(4), beta(6)}.

  14. Baran, A. Sieja, K., Neutron-proton pairing in Ge-64, International Journal of Modern Physics E-Nuclear Physics, 14(3), 2005, 445-450

    Abstract:
    Isotopes of germanium are studied in the framework of the relativistic mean-field theory with a delta-pairing type residual interaction. Both pairing channels T = 1 and T = 0 are included. The T = 0 channel does not contribute to the pairing energy even with a large coupling strength of the delta force. It is shown that the Wigner-like term (congruence energy) may be partly reproduced by T = 1, T-z = 0 neutron-proton pairing which is remarkably strong in the case of Z = N nuclei.

  15. Baran, A. Lojewski, Z. Sieja, K., Masses and half-lives of superheavy elements, Acta Physica Polonica B, 36(4), 2005, 1369-1372

    Abstract:
    Spontaneous fission and alpha-decay half-lives of superheavy elements are determined in the macroscopic-microscopic model where the macroscopic part is the Lublin-Strasbourg Drop and the pairing correction is based on the state-dependent two-body interaction of the 6 type. The coupling strengths of the pairing force are fitted to experimentally known masses of heavy nuclei with Z >= 98.

  16. Baran, A. Mierzynski, P., Bethe plots and neutron halo, Acta Physica Polonica B, 35(9), 2004, 2293-2301

    Abstract:
    The relative excess of a neutron density introduced by Bethe is applied to classify atomic nuclei with respect to a neutron halo. Calculations are based on the relativistic mean field model and are performed for 116 spherically symmetric nuclei across the periodic system of elements and for a group of deformed nuclei studied in antiproton annihilation reaction at the LEAR facility in CERN. Basic properties of the neutron excess function are discussed.

  17. Sieja, K. Baran, A. Pomorski, K., delta-pairing forces and collective pairing vibrations, European Physical Journal A, 20(3), 2004, 413-418

    Abstract:
    The collective pairing Hamiltonian is obtained in the framework of the generator coordinate method in the Gaussian overlap approximation with a slightly modified BCS function used as a generator function. The collective variable alpha, measuring the monopole moment of the pairing field, and the gauge transformation angle phi are chosen as generator coordinates. The vibrational ground states are calculated by diagonalisation of the collective pairing Hamiltonian in the harmonic- oscillator basis.

  18. Baran, A. Sieja, K., Comparison of delta- and Gogny-type pairing interactions, Acta Physica Polonica B, 35(3), 2004, 1291-1297

    Abstract:
    The matrix elements of the zero-range delta-force and the finite range Gogny-type pairing force are compared. The strengths of the delta-interaction for rare-earth nuclei are adjusted. Pairing gaps resulting from different pairing interactions are compared to experimental ones.

  19. Baran, A. Sieja, K., delta-pairing forces and nuclear masses, International Journal of Modern Physics E-Nuclear Physics, 13(1), 2004, 113-116

    Abstract:
    The delta-pairing strengths for rare-earth nuclei axe estimated from nuclear masses of odd and even systems. The masses axe calculated for a variety of macroscopic and microscopic models. We use the BCS and Lipkin-Nogami methods, with a blocking effect in case of odd nuclei. The rms mass deviations obtained in different models axe from 0.66 to 1.46.

  20. Baran, A. Mierzynski, P., Nuclear periphery in mean-field models, International Journal of Modern Physics E-Nuclear Physics, 13(1), 2004, 337-341

    Abstract:
    The halo factor is one of the experimental data which describes a distribution of neutrons in the nuclear periphery. In the presented paper we use Skyrme-Hartree (SH) and the Relativistic Mean Field (RMF) models to calculate the neutron excess factor Delta(B) which differs slightly from the halo factor f(exp). The results of the calculations are compared to the measured data.

  21. Baran, A. Lojewski, Z. Sieja, K., State dependent delta-pairing and spontaneous fission, International Journal of Modern Physics E-Nuclear Physics, 13(1), 2004, 353-356

    Abstract:
    We examine the fission barriers, mass parameters and spontaneous fission half lives of Fermium isotopes within the framework of the macroscopic-microscopic model with a delta- pairing interaction. Four different macroscopic models are applied and studied. The results are compared to experimental data and to the ones of the corresponding monopole pairing approach. The half lives obtained in the delta-pairing model axe comparable with experimental data.

  22. Sieja, K. Baran, A., State dependent delta-pairing force with Nilsson models: Nuclear shapes, radii, and masses, Physical Review C, 68(4), 2003, art. no.-044308

    Abstract:
    The single particle Nilsson as well as Nilsson-Seo-type potentials and the state dependent delta-pairing force are used to calculate nuclear deformations, root-mean square charge radii, quadrupole moments, and masses of rare earth nuclei. The masses are evaluated by means of Strutinsky shell correction method where the macroscopic part of the energy is the recently developed Lublin-Skrasbourg drop model and the microscopic energy is the sum of shell and pairing corrections. The latter is based on the delta-force pairing interaction, the strength of which is adjusted to the three-mass pairing indicators Delta((3)) calculated from the experimental nuclear masses. The results are compared to experimental data and to estimates done in other models. The agreement of our results with the measured data is acceptable. The standard deviation for calculated masses is about 0.8 MeV. The results show that the state dependent delta-pairing force works similarly as in the monopole pairing models.

  23. Lojewski, Z. Baran, A. Pomorski, K., Spontaneous fission and alpha-decay half-lives of superheavy nuclei in different macroscopic energy models, Acta Physica Polonica B, 34(3), 2003, 1801-1813

    Abstract:
    Spontaneous fission half-lives (T-sf) of the heaviest nuclei are calculated in the macroscopic-microscopic approach based on the deformed Woods-Saxon potential. Four different models of the macroscopic energy are examined and their influence on the results is discussed. The calculations of (T-sf) are performed within WKB approximation. Multi-dimensional dynamical- programming method (MDP) is applied to minimize the action integral in a 3-dimensional space of deformation parameters describing the nuclear shape {beta(2), beta(4), beta(6) }.

  24. Baran, A., Relativistic mean field antinucleon-nucleus potential, Acta Physica Polonica B, 32(3), 2001, 1025-1031

    Abstract:
    The real Dart of antinucleon-nucleus potential is determined in the framework of the Relativistic Mean Field model using the charge conjugation. The solution of the Dirac equation for antiproton is given in case of Pb-208. The bound state antiprotonic wave functions are compared to those obtained front the pure point charge Coulomb potential. The spectrum of (p) over bar is shown.

  25. Baran, A. Lojewski, Z., Single particle nuclear levels in Extended Thomas-Fermi potentials, Acta Physica Polonica B, 31(2), 2000, 411-416

    Abstract:
    Single particle nuclear levels are calculated on the basis of the potentials derived from the Extended Thomas-Fermi type Skyrme models for the Skyrme forces Skill, SkM* and SLy4.

  26. Lojewski, Z. Baran, A., Spontaneous fission and alpha-decay half-lives of superheavy nuclei, Acta Physica Polonica B, 31(2), 2000, 485-493

    Abstract:
    Spontaneous fission and alpha-decay half-lives of even-even superheavy nuclei 112 less than or equal to Z less than or equal to 120 are calculated on the basis of the deformed Woods- Saxon potential in WKB approximation by the multi-dimensional dynamical programing method in space of parameters describing the shape of nuclei {beta(2),beta(4),beta(6)} and the pairing degrees of freedom {Delta(p),Delta(n)}. The direct comparisons of the spontaneous fission and alpha-decay half-lives calculated by the Viola-Seaborg formula establish the regions of dominance of the spontaneous fission and the alpha mode of desintegration.

  27. Baran, A., Relativistic mean field calculations of single particle potentials, Physical Review C, 6102(2), 2000, art. no.-024316

    Abstract:
    The parameters of form factors representing single particle central, spin-orbit, and Coulomb potentials as well as the effective nucleon mass are extracted from the relativistic mean field model of nuclei. The central and the spin-orbit nuclear potentials are proportional to the sum and the difference of the relativistic scalar- and vector-meson potentials, respectively. The latter enter the Dirac equation of the nucleon. The form factors representing the potentials are parametrized in terms of Woods-Saxon functions. They reproduce nearly exactly the single particle spectra of the self- consistent relativistic mean field theory. The effective mass is parametrized in the similar fashion. The Coulomb single particle potential parameters for protons are given as well. Calculations are based on the 116 spherically symmetric even- even nuclei from light (A = 16) to heavy (A = 220) ones, with known mass.

  28. Patyk, Z. Baran, A. Berger, J. F. Decharge, J. Dobaczewski, J. Ring, P. Sobiczewski, A., Masses and radii of spherical nuclei calculated in various microscopic approaches, Physical Review C, 59(2), 1999, 704-713

    Abstract:
    The quality of the description of nuclear masses and charge radii, calculated in various microscopic approaches, is studied. The Hartree-Fock-Bogoliubov (HFB), extended Thomas- Fermi model with Strutinski integral (ETFSI), relativistic mean field (RMF), and macroscopic-microscopic (MM) approaches are considered. In the HFB approximation, both finite-range (Gogny) and zero-range (Skyrme) effective forces are used. Spherical even-even nuclei (116 nuclides), from light (A=16) to heavy (A=220) ones, with known experimental mass are chosen for the study. A general result is that the best description of masses of considered nuclei is obtained in the MM and ETFSI approaches, while the best charge radii are obtained within the RMF and ETFSI approximations. The behavior of nuclear masses and radii, when one moves far off the beta-stability line, is also studied. [S0556-2813(99)00102-8].

  29. Pomorski, K. Ring, P. Lalazissis, G. A. Baran, A. Lojewski, Z. NerloPomorska, B. Warda, M., Ground state properties of the beta stable nuclei in various mean field theories, Nuclear Physics A, 624(3), 1997, 349-369

    Abstract:
    The separation energies of neutrons and protons, binding energies, mean square charge radii, electric quadrupole moments and deformation parameters of the proton and neutron distributions are evaluated for beta stable even-even nuclei with 16 less than or equal to A less than or equal to 256. We compare the theoretical estimates obtained within the Hartree- Fock plus BCS model with a few sets of Skyrme forces, relativistic mean-field theory and frequently used Saxon-Woods and Nilsson potentials with experimental data. (C) 1997 Elsevier Science B.V.

  30. Baran, A. Pomorski, K. Warda, M., Neutron halos in heavy nuclei-relativistic mean field approach, Zeitschrift Fur Physik a-Hadrons and Nuclei, 357(1), 1997, 33-38

    Abstract:
    Assuming a simple spherical relativistic mean field model of the nucleus, we estimate the width of the antiproton-neutron annihilation (Gamma(n)) and the width of antiproton-proton (Gamma(p)) annihilation, in an antiprotonic atom system. This allows us to determine the halo factor f, which is then discussed in the context of experimental data obtained in measurements recently done on LEAR utility at CERN. Another quantity which characterizes the deviation of the average nuclear densities ratio from the corresponding ratio of the homogeneous densities is introduced too. It was shown that it is also a good indicator of the neutron halo. The results are compared to experimental data as well as to the data of the simple liquid droplet model of the nuclear densities. The single particle structure of the nuclear density tail is discussed also.

  31. Baran, A. Hohenberger, W., Gd isotope systematics with Skyrme and delta-pairing forces, Physical Review C, 53(4), 1996, 1571-1579

    Abstract:
    Assuming axial symmetry of the nuclear shape and the Skyrme force SIII updated on the pairing interaction V-0 delta((r) over right arrow(12)) we performed constrained Hartree-Fock calculations of well deformed even gadolinium Gd-64 isotopes with neutron numbers N=86-106. The mass spectrum, nuclear radii, neutron skin thickness, quadrupole moments (deformations), and low-spin rotational levels are calculated. In all the cases viewed the angular momentum projection after variation was performed. This was achieved by explicit inclusion of the rotational energy - [(j) over cap(2)]/2J. The procedure corrects the ground state deformations and gives deformations and energies of low excited states as well. The results found have all been compared to experimental data.

  32. Patyk, Z. Baran, A. Berger, J. F. Decharge, J. Dobaczewski, J. Smolanczuk, R. Sobiczewski, A., On the quality of microscopic descriptions of nuclear mass, Acta Physica Polonica B, 27(1-2), 1996, 457-462

    Abstract:
    The quality of the description of nuclear masses by various microscopic approaches is studied. Hartree-Fock-Bogolubov, Extended Thomas-Fermi model with Strutinski Integral, Relativistic Mean Field and Macroscopic-Microscopic approaches are considered. Spherical even-even nuclei (116 nuclides) from light (A = 16) to heavy (A = 220) ones with known experimental mass are chosen for the study.


[ powrót do pełnej listy pracowników ]