Dao T. Khoa

Vietnam Atomic Energy Institute, Hà Nội, Ha Nội, Vietnam

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Publications (90)225.34 Total impact

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    ABSTRACT: The folding model analysis of the elastic $\alpha + \alpha$ scattering at the incident energies below the reaction threshold of 34.7 MeV (in the lab system) has been done using the well-tested density dependent versions of the M3Y interaction and realistic choices for the $^4$He density. Because the absorption is negligible at the energies below the reaction threshold, we were able to probe the $\alpha + \alpha$ optical potential at low energies quite unambiguously and found that the $\alpha + \alpha$ overlap density used to construct the density dependence of the M3Y interaction is strongly distorted by the Pauli blocking. This result gives possible explanation of a long-standing inconsistency of the double-folding model in its study of the elastic $\alpha + \alpha$ and $\alpha$-nucleus scattering at low energies using the same realistic density dependent M3Y interaction.
    03/2014;
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    ABSTRACT: The charge-exchange (3He,t) scattering to the isobaric analog state (IAS) of the target can be considered as "elastic" scattering of 3He by the isovector term of the optical potential (OP) that flips the projectile isospin. Therefore, the accurately measured charge-exchange scattering cross- section for the IAS can be a good probe of the isospin dependence of the OP, which is determined exclusively within the folding model by the difference between the neutron and proton densities and isospin dependence of the nucleon-nucleon interaction. Given the neutron skin of the target is related directly to the same density difference, it can be well probed in the analysis of the charge- exchange (3He,t) reactions at medium energies when the two-step processes can be neglected and the t-matrix interaction can be used in the folding calculation. For this purpose, the data of the (3He,t) scattering to the IAS of 90Zr and 208Pb targets at Elab = 420 MeV have been analyzed in the distorted wave Born approximation using the double-folded charge-exchange form factor. The neutron skin deduced for these two nuclei turned out to be in a good agreement with the existing database.
    Physical Review C 02/2014; 89(2). · 3.72 Impact Factor
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    ABSTRACT: An elaborate folding model + coupled channel analysis of the inelastic α+12C scattering has been done using the inelastic form factors based on the nuclear transition densities predicted by the antisymmetrized molecular dynamics. The form factors for the observed isoscalar states of 12C were fine-tuned against the measured (α, α') cross sections to estimate the corresponding Eλ transition strengths. A significant E2 transition strength has been allocated for the second 2+ state of 12C from our consistent coupled channel analysis of the (α, α') data measured at Eα = 240 and 386 MeV. The Eλ transition strengths of the 0+2, 3-1, 0+3, and 1-1 states were also carefully deduced from the same folding model + coupled channel analysis.
    Journal of Physics Conference Series 01/2014; 569(1).
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    ABSTRACT: The complex optical potential and inelastic form factor given by the folding model for the $\alpha+^{12}$C scattering are used to calculate the ($\alpha,\alpha'$) cross sections for the known isoscalar states of $^{12}$C in an elaborate coupled channel approach. The strengths of the form factors for these states are then fine tuned against the ($\alpha,\alpha'$) data to deduce the corresponding $E\lambda$ transition strengths. A significant $E2$ transition strength has been obtained for the $2^+_2$ state from the present analysis of the ($\alpha,\alpha'$) data measured at $E_\alpha=240$ and 386 MeV. The $E\lambda$ transition strengths of the $0^+_2,\ 3^-_1,\ 0^+_3,$ and $1^-_1$ states were also carefully deduced, and some difference from the results of earlier analyses has been found and qualitatively understood.
    12/2013;
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    ABSTRACT: The Fermi transition (\Delta L=\Delta S=0 and \Delta T=1) between the nuclear isobaric analog states (IAS), induced by the charge-exchange (p,n) or (3He,t) reaction, can be considered as "elastic" scattering of proton or 3He by the isovector term of the optical potential (OP) that flips the projectile isospin. The accurately measured (p,n) or (3He,t) scattering cross-section to the IAS can be used, therefore, to probe the isospin dependence of the proton or 3He optical potential. Within the folding model, the isovector part of the OP is determined exclusively by the neutron-proton difference in the nuclear densities and the isospin dependence of the effective nucleon-nucleon (NN) interaction. Because the isovector coupling explicitly links the isovector part of the proton or 3He optical potential to the cross section of the charge-exchange (p,n) or (3He,t) scattering to the IAS, the isospin dependence of the effective (in-medium) NN interaction can be well tested in the folding model analysis of these charge-exchange reactions. On the other hand, the same isospin- and density dependent NN interaction can also be used in a Hartree-Fock calculation of asymmetric nuclear matter, to estimate the nuclear matter energy and its asymmetry part (the nuclear symmetry energy). As a result, the fine-tuning of the isospin dependence of the effective NN interaction against the measured (p,n) or (3He,t) cross sections should allow us to make some realistic prediction of the nuclear symmetry energy and its density dependence.
    07/2013;
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    ABSTRACT: Analysis of data involving nuclei far from stability often requires optical potential (OP) for neutron scattering. Since neutron data is seldom available, while proton scattering data is more abundant, it is useful to have estimates of the difference of the neutron and proton optical potentials. This information is contained in the isospin dependence of the nucleon OP. Here we attempt to provide it for the nucleon-208Pb system. The goal of this paper is to obtain accurate n+208Pb scattering data, and use it, together with existing p+208Pb and 208Pb(p,n)208$Bi*_{IAS} data, to obtain an accurate estimate of the isospin dependence of the nucleon OP at energies in the 30-60 MeV range. Cross sections for n+208Pb scattering were measured at 30.4 and 40.0 MeV, with a typical relative (normalization) accuracy of 2-4% (3%). An angular range of 15 to 130 degrees was covered using the beam-swinger time of flight system at Michigan State University. These data were analyzed by a consistent optical model study of the neutron data and of elastic p+208Pb scattering at 45 MeV and 54 MeV. These results were combined with a coupled-channel analysis of the 208Pb(p,n) reaction at 45 MeV, exciting the 0^+ isobaric analog state in 208Bi. The new data and analysis give an accurate estimate the isospin impurity of the nucleon-208Pb OP at 30.4 MeV, caused by the Coulomb correction to the proton OP. The corrections to the real proton OP given by the CH89 global systematics was found to be only few percent, while for the imaginary potential it was over 20% at the nuclear surface. Based on the analysis of the measured elastic p+208Pb data at 40 MeV, a Coulomb correction of similar strength and shape was also predicted for the p+208Pb OP at energy around 54 MeV.
    Physical Review C 02/2012; 85(2). · 3.72 Impact Factor
  • Dao T.khoa, W.von Oertzen, H. G.bohlen
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    ABSTRACT: We present a brief overview of the light wave interference in the atmospheric rainbow and how a similar mechanism can be observed in the elastic nucleus-nucleus scattering which gives rise to the nuclear rainbow. The latter phenomenon, observed at energies of around few tens MeV/nucleon, has been well investigated based on the basic concepts of the nuclear optical model. Given a weak absorption associated with the nuclear rainbow scattering, the observed data can be used to probe the density dependence of the effective nucleon-nucleon (NN) interaction based on the folding model study of elastic scattering. Most of the rainbow scattering data were found to be best described by a density dependent NN interaction which gives a nuclear incompressibility K ≈ 230 – 260 MeV in the Hartree-Fock calculation of nuclear matter. This result implies a rather soft equation of state of nuclear matter.
    International Journal of Modern Physics B 01/2012; 22(25n26). · 0.46 Impact Factor
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    ABSTRACT: The nuclear mean-field potentials obtained in the Hartree-Fock method with different choices of the in-medium nucleon-nucleon (NN) interaction have been used to study the equation of state (EOS) of the neutron star (NS) matter. The EOS of the uniform NS core has been calculated for the np$e\mu$ composition in the $\beta$-equilibrium at zero temperature, using version Sly4 of the Skyrme interaction as well as two density-dependent versions of the finite-range M3Y interaction (CDM3Y$n$ and M3Y-P$n$), and versions D1S and D1N of the Gogny interaction. Although the considered effective NN interactions were proven to be quite realistic in numerous nuclear structure and/or reaction studies, they give quite different behaviors of the symmetry energy of nuclear matter at supranuclear densities that lead to the \emph{soft} and \emph{stiff} scenarios discussed recently in the literature. Different EOS's of the NS core and the EOS of the NS crust given by the compressible liquid drop model have been used as input of the Tolman-Oppenheimer-Volkov equations to study how the nuclear symmetry energy affects the model prediction of different NS properties, like the cooling process as well as the gravitational mass, radius, and moment of inertia.
    Physical Review C 05/2011; 83(6). · 3.72 Impact Factor
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    ABSTRACT: While the Hoyle state (the isoscalar 02+ excitation at 7.65 MeV in 12C) has been observed in almost all the electron and alpha inelastic scattering experiments, the second 2+ excited state of 12C at E≈10 MeV, believed to be an excitation of the Hoyle state, has not been clearly observed in these measurements excepting the high-precision (alpha,alpha')C12 experiments at E=240 and 386 MeV. Given the (spin and isospin zero) alpha-particle as a good probe for the nuclear isoscalar excitations, it remains a puzzle why the peak of the 22+ state could not be clearly identified in the measured (alpha,alpha')C12 spectra. To investigate this effect, we have performed a microscopic folding model analysis of the alpha+C12 scattering data at 240 and 386 MeV in both the Distorted Wave Born Approximation (DWBA) and coupled-channel (CC) formalism, using the nuclear transition densities given by the antisymmetrized molecular dynamics (AMD) approach and a complex CDM3Y6 density dependent interaction. Although AMD predicts a very weak transition strength for the direct (01+-->22+) excitation, our detailed analysis has shown evidence that a weak ghost of the 22+ state could be identified in the 240 MeV (alpha,alpha')C12 data for the 03+ state at 10.3 MeV, when the CC effects by the indirect excitation of the 22+ state are taken into account. Based on the same AMD structure input and preliminary (alpha,alpha')C12 data at 386 MeV, we have estimated relative contributions from the 22+ and 03+ states to the excitation of 12C at E≈10 MeV as well as possible contamination by 31- state.
    Physics Letters B 01/2011; 695:469-475. · 4.57 Impact Factor
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    ABSTRACT: The energetic beam of (spin and isospin zero) α-particles remains a very efficient probe for the nuclear isoscalar giant resonances. In the present work, a microscopic folding model study of the isoscalar giant resonances in 208Pb induced by inelastic scattering at Elab=240 and 386 MeV has been performed using the (complex) CDM3Y6 interaction and nuclear transition densities given by both the collective model and Random Phase Approximation (RPA) approach. The fractions of energy weighted sum rule around the main peaks of the isoscalar monopole, dipole and quadrupole giant resonances were probed in the Distorted Wave Born Approximation analysis of inelastic scattering using the double-folded form factors given by different choices of the nuclear transition densities. The energy distribution of the E0, E1 and E2 strengths given by the multipole decomposition analyses of the (α,α′) data under study are compared with those predicted by the RPA calculation.
    Nuclear Physics A 01/2010; · 2.50 Impact Factor
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    ABSTRACT: The two recent density-dependent versions of the finite-range M3Y interaction (CDM3Y$n$ and M3Y-P$n$) have been probed against the bulk properties of asymmetric nuclear matter (NM) in the nonrelativistic Hartree Fock (HF) formalism. The same HF study has also been done with the famous Skyrme (SLy4) and Gogny (D1S and D1N) interactions which were well tested in the nuclear structure calculations. Our HF results are compared with those given by other many-body calculations like the Dirac-Brueckner Hartree-Fock approach or ab-initio variational calculation using free nucleon-nucleon interaction, and by both the nonrelativistic and relativistic mean-field studies using different model parameters. Although the two considered density-dependent versions of the M3Y interaction were proven to be quite realistic in the nuclear structure or reaction studies, they give two distinct behaviors of the NM symmetry energy at high densities, like the Asy-soft and Asy-stiff scenarios found earlier with other mean-field interactions. As a consequence, we obtain two different behaviors of the proton fraction in the $\beta$-equilibrium which in turn can imply two drastically different mechanisms for the neutron star cooling. While some preference of the Asy-stiff scenario was found based on predictions of the latest microscopic many-body calculations or empirical NM pressure and isospin diffusion data deduced from heavy-ion collisions, a consistent mean-field description of nuclear structure database is more often given by some Asy-soft type interaction like the Gogny or M3Y-P$n$ ones. Such a dilemma poses an interesting challenge to the modern mean-field approaches. Comment: Version accepted for publication in Phys. Rev. C
    Physical Review C 12/2009; · 3.72 Impact Factor
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    Nguyen Dang Chien, Dao T. Khoa
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    ABSTRACT: A coupled-channel analysis of the $^{18,20,22}$O$(p,p')$ data has been performed to determine the neutron transition strengths of 2$^+_1$ states in Oxygen targets, using the microscopic optical potential and inelastic form factor calculated in the folding model. A complex density- and \emph{isospin} dependent version of the CDM3Y6 interaction was constructed, based on the Brueckner-Hatree-Fock calculation of nuclear matter, for the folding model input. Given an accurate isovector density dependence of the CDM3Y6 interaction, the isoscalar ($\delta_0$) and isovector ($\delta_1$) deformation lengths of 2$^+_1$ states in $^{18,20,22}$O have been extracted from the folding model analysis of the $(p,p')$ data. A specific $N$-dependence of $\delta_0$ and $\delta_1$ has been established which can be linked to the neutron shell closure occurring at $N$ approaching 16. The strongest isovector deformation was found for 2$^+_1$ state in $^{20}$O, with $\delta_1$ about 2.5 times larger than $\delta_0$, which indicates a strong core polarization by the valence neutrons in $^{20}$O. The ratios of the neutron/proton transition matrix elements ($M_n/M_p$) determined for 2$^+_1$ states in $^{18,20}$O have been compared to those deduced from the mirror symmetry, using the measured $B(E2)$ values of 2$^+_1$ states in the proton rich $^{18}$Ne and $^{20}$Mg nuclei, to discuss the isospin impurity in the $2^+_1$ excitation of the $A=18,T=1$ and $A=20,T=2$ isobars.
    Physical Review C 01/2009; 79(3). · 3.72 Impact Factor
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    Dao T. Khoa
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    ABSTRACT: The robust (spin and isospin zero) $\alpha$-particle remains one of the best projectiles to probe the nuclear isoscalar excitations. In the present work, a microscopic folding model analysis of the \ac inelastic scattering to the 2$^+$ (4.44 MeV), 0$^+$ (7.65 MeV), 3$^-$ (9.64 MeV), 0$^+$ (10.3 MeV) and 1$^-$ (10.84 MeV) states in $^{12}$C has been performed using the 3-$\alpha$ resonating group method wave functions. The isoscalar transition strengths of these states were carefully studied based on the coupled-channel analysis using the microscopic folded form factors. A correlation between the weak binding and/or short lifetime of the excited state and absorption in the exit channel of inelastic scattering has been established. Comment: Talk given at SOTANCP Workshop, Strasbourg, May 2008; to appear in International Journal of Modern Physics E
    International Journal of Modern Physics E 06/2008; · 0.63 Impact Factor
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    ABSTRACT: A method of solving in coordinate representation the Hartree-Fock (HF) equations with finite-range interactions is presented. The calculations are performed with the effective Gogny interaction D1S. Results for the continuum properties of the single-particle spectra in Oxygen isotopes are discussed. The present method can be extended to treat the HF-BCS problem in neutron-rich nuclei with inclusion of the resonant continuum.
    04/2008;
  • Do Cong Cuong, Dao Tien Khoa
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    ABSTRACT: Microscopic folding model analysis of the inelastic alpha+12C scattering to 0+2 and 2+1 states in 12C at Elab = 104 to 240 MeV has been done using the 3-alpha resonating group wave functions and a complex density-dependent M3Y interaction deduced from the Brueckner Hartree Fock results for nuclear matter. In difference from 2+1 excitation at 4.44 MeV, the DWBA or CC analyses show that the strength of the 0+2 state at 7.65 MeV (the Hoyle state) exhausts only 7% of the monopole energy weighted sum rule (EWSR), compared to about 15% of the EWSR extracted from inelastic electron scattering data. The full E0 transition strength predicted by microscopic alpha-cluster models of the Hoyle state can be shown to exhaust up to 22% of the EWSR. Our present study has found that the missing E0 strength of the Hoyle state is likely due to the short lifetime and weakly bound structure of 0+2 state which significantly enhance absorption in the exit alpha +12C*(0+2) channel.
    04/2008;
  • 01/2008;
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    ABSTRACT: We present a brief overview of the light wave interference in the atmospheric rainbow and how a similar mechanism can be observed in the elastic nucleus nucleus scattering, which gives rise to the nuclear rainbow. The latter phenomenon, observed at energies of around few tens MeV nucleon, has been well investigated based on the basic concepts of the nuclear optical model. Given a weak absorption associated with the nuclear rainbow scattering, the observed data can be used to probe the density dependence of the effective nucleon nucleon NN interaction based on the folding model study of elastic scattering. Most of the rainbow scattering data were found to be best described by a density dependent NN interaction, which gives a nuclear incompressibility K 260 MeV in the Hartree Fock calculation of nuclear matter. This result implies a rather soft equation of state of nuclear matter
    International Journal of Modern Physics B 01/2008; · 0.46 Impact Factor
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    Dao T. Khoa, Do Cong Cuong
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    ABSTRACT: Analyses of the inelastic α+12C scattering at medium energies have indicated that the strength of the Hoyle state (the isoscalar excitation at 7.65 MeV in 12C) seems to exhaust only 7–9% of the monopole energy weighted sum rule (EWSR), compared to about 15% of the EWSR extracted from inelastic electron scattering data. The full monopole transition strength predicted by realistic microscopic α-cluster models of the Hoyle state can be shown to exhaust up to 22% of the EWSR. To explore the missing monopole strength in the inelastic α+12C scattering, we have performed a fully microscopic folding model analysis of the inelastic α+12C scattering at Elab=104–240 MeV using the 3-α resonating group wave function of the Hoyle state obtained by Kamimura, and a complex density-dependent M3Y interaction newly parametrized based on the Brueckner–Hartree–Fock results for nuclear matter. Our folding model analysis has shown consistently that the missing monopole strength of the Hoyle state is not associated with the uncertainties in the analysis of the α+12C scattering, but is most likely due to the short lifetime and weakly bound structure of this state which significantly enhances absorption in the exit channel.
    Physics Letters B 01/2008; · 4.57 Impact Factor
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    D. T. Khoa
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    ABSTRACT: DWBA analysis of the inelastic 30-40S(p,p') and 18-22O(p,p') scattering data measured in the inverse kinematics has been performed to determine the isoscalar (δ0) and isovector (δ1) deformation lengths of the 2+1 excitations in the Sulfur and Oxygen isotopes using a compact folding approach. A systematic N-dependence of δ0 and δ1 has been established which shows a link between δ1 and the neutron-shell closure. Strong isovector deformations were found in several cases, e.g., the 2+1 state in 20O where δ1 is nearly three times larger than δ0. These results confirm the relation δ1>δ0 anticipated from the core polarization by the valence neutrons in the open-shell (neutron rich) nuclei. The effect of neutron shell closure at N=14 or 16 has been discussed based on the folding model analysis of the inelastic 22O+p scattering data at 46.6 MeV/u measured recently at GANIL.
    The European Physical Journal Special Topics 10/2007; 150(1):31-34. · 1.80 Impact Factor
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    Dao T. Khoa, Do Cong Cuong
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    ABSTRACT: A new finite-range representation of the JLM effective nucleon-nucleon interaction is suggested based on the CDM3Y density dependent functional and M3Y-Paris interaction. The density dependence has been carefully adjusted at each energy so that the nucleon optical potential (OP) given by the new density dependent interaction in the Hartree-Fock calculation of nuclear matter closely matches the JLM nucleon OP given by the Brueckner-Hatree-Fock calculation. The new interaction has been used in the double-folding model to calculate the OP for the elastic $^{6}$Li,$^{6}$He,$^{12}$C + $^{12}$C scattering at different energies.
    09/2007;

Publication Stats

2k Citations
225.34 Total Impact Points

Institutions

  • 2007
    • Vietnam Atomic Energy Institute
      Hà Nội, Ha Nội, Vietnam
  • 2006
    • Institut de Physique Nucléaire de Lyon
      Lyons, Rhône-Alpes, France
  • 2003
    • Florida State University
      • Department of Physics
      Tallahassee, FL, United States
  • 2002
    • Università degli Studi del Sannio
      Benevento, Campania, Italy
  • 1995–2000
    • University of Tennessee
      Knoxville, Tennessee, United States
  • 1998
    • University of Barcelona
      Barcino, Catalonia, Spain
  • 1997–1998
    • Chung Yuan Christian University
      臺中市, Taiwan, Taiwan
  • 1996
    • Freie Universität Berlin
      Berlín, Berlin, Germany
  • 1991
    • University of Tuebingen
      • Institute of Physical and Theoretical Chemistry
      Tübingen, Baden-Wuerttemberg, Germany
    • Universität Heidelberg
      • Institute of Theoretical Physics
      Heidelberg, Baden-Wuerttemberg, Germany
    • Minia University
      • Department of Physics
      Minyat an Naşr, Muhafazat ad Daqahliyah, Egypt
  • 1987–1988
    • Joint Institute for Nuclear Research
      Dubno, Moskovskaya, Russia
    • Leningrad State University
      Sankt-Peterburg, St.-Petersburg, Russia