arXiv subjects

N. Vinh Mau

Publications and source records attributed to N. Vinh Mau.

8 recordsLinked to original sources

arXiv2014

Microscopic positive-energy potential based on Gogny interaction

We present nucleon elastic scattering calculation based on Green's function formalism in the Random-Phase Approximation. For the first time, the Gogny effective interaction is used consistently throughout the whole calculation to account for the complex, non-local and energy-dependent optical potential. Effects of intermediate single-particle resonances are included and found to play a crucial role in the account for measured reaction cross section. Double counting of the particle-hole second-order contribution is carefully addressed. The resulting integro-differential Schrödinger equation for the scattering process is solved without localization procedures. The method is applied to neutron and proton elastic scattering from $^{40}$Ca. A successful account for differential and integral cross sections, including analyzing powers, is obtained for incident energies up to 30 MeV. Discrepancies at higher energies are related to much too high volume integral of the real potential for large partial waves. Moreover, this works opens the way for future effective interactions suitable simultaneously for both nuclear structure and reaction.

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arXiv2007

Unbound exotic nuclei studied by projectile fragmentation

We call "projectile fragmentation" of neutron halo nuclei the elastic breakup (diffraction) reaction, when the observable studied is the neutron-core relative energy spectrum. This observable has been measured in relation to the Coulomb breakup on heavy target and recently also on light targets. Such data enlighten the effect of the neutron final state interaction with the core of origin. Projectile fragmentation is studied here by a time dependent model for the excitation of a nucleon from a bound state to a continuum resonant state in a neutron-core complex potential which acts as a final state interaction. The final state is described by an optical model S-matrix so that both resonant and non resonant states of any continuum energy can be studied as well as deeply bound initial states. It turns out that due to the coupling between the initial and final states, the neutron-core free particle phase shifts are modified, in the exit channel, by an additional phase. Some typical numerical calculations for the relevant observables are presented and compared to experimental data. It is suggest that the excitation energy spectra of an unbound nucleus might reflect the structure of the parent nucleus from whose fragmentation they are obtained.

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arXiv2007

$^{10}$Li spectrum from $^{11}$Li fragmentation

A recently developed time dependent model for the excitation of a nucleon from a bound state to a continuum resonant state in the system n+core is applied to the study of the population of the low energy continuum of the unbound $^{10}$Li system obtained from $^{11}$Li fragmentation. Comparison of the model results to new data from the GSI laboratory suggests that the reaction mechanism is dominated by final state effects rather than by the sudden process, but for the population of the l=0 virtual state, in which case the two mechanisms give almost identical results. There is also, for the first time, a clear evidence for the population of a d$_{5/2}$ resonance in $^{10}$Li.

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arXiv2006

Unbound exotic nuclei studied by projectile fragmentation

We present a simple time dependent model for the excitation of a nucleon from a bound state to a continuum resonant state in a neutron-core complex potential which acts as a final state interaction. The final state is described by an optical model S-matrix so that both resonant and non resonant states of any continuum energy can be studied as well as deeply bound initial states. It is shown that, due to the coupling between the initial and final states, the neutron-core free particle phase shifts are modified, in the exit channel, by an additional phase. The effect of the additional phase on the breakup spectra is clarified. As an example the population of the low energy resonances of $^{11}$Be and of the unbound $^{13}$Be is discussed. Finally, we suggest that the excitation energy spectra of an unbound nucleus might reflect the structure of the parent nucleus from whose fragmentation they are obtained.

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arXiv2004

Unbound exotic nuclei studied by transfer to the continuum reactions

In this paper we show that the theory of transfer reactions from bound to continuum states is well suited to extract structure information from data obtained by performing "spectroscopy in the continuum". The low energy unbound states of nuclei such as $^{10}$Li and $^{5}$He can be analyzed and the neutron-core interaction, necessary to describe the corresponding borromean nuclei $^{11}$Li and $^{6}$He can be determined in a semi-phenomenological way. An application to the study of $^{10}$Li is then discussed and it is shown that the scattering length for s-states at threshold can be obtained from the ratio of experimental and theoretical cross sections. The scattering single particle states of the system n+$^{9}$Li are obtained in a potential model. The corresponding S-matrix is used to calculate the transfer cross section as a function of the neutron continuum energy with respect to $^{9}$Li. Three different reactions are calculated $^{9}Li(d,p)^{10}Li$, $^{9}Li(^{9}Be,^{8}Be)^{10}Li$, $^{9}Li(^{13}C,^{12}C)^{10}Li$, to check the sensitivity of the results to the target used and in particular to the transfer matching conditions. Thus the sensitivity of the structure information extracted from experimental data on the reaction mechanism is assessed.

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arXiv2001

Two-body correlations in N=8 and 10 nuclei and effective neutron-neutron interactions in Tamm-Dancoff and two-particle RPA models

We apply a particle-particle RPA model to study the properties of the two-neutron valence wave function in nuclei 14-C, 12-Be, 11-Li and 14-Be. The RPA model takes account of two body correlations in the core so that it gives a better description of energies and amplitudes than models which assume a neutron closed shell (or subshell) core. With a Gogny neutron-neutron effective interaction or with the equivalent density dependent delta force we are able to reproduce the two-neutron separation energies in these nuclei and in the corresponding cores, except for 9-Li. These calculations suggest the same 2s-1p1/2 shells inversion in 12-Be_13-Be than in 11-Be.

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arXiv2000

Reaction and break-up cross sections of 11Li at 0.8 and 0.28 GeV/u

In this paper we calculate reaction and breakup cross sections for the two- neutron halo nucleus of $^{11}$Li using the optical limit of Glauber theory. Calculations are presented and compared to experimental data at 0.8 and 0.28 GeV/u on a series of targets. The $^{11}$Li nucleus is described as a three-body system, a core plus two neutrons, with a phenomenological neutron-core potential and a density dependent neutron-neutron interaction of zero range. Three different wave functions are constructed which have different $(2s_{1/2})^2$ and $(1p_{1/2})^2$ two-neutron components but correspond to the same binding energy close to the experimental value. We show that the agreement with all the experimental observables is achieved only if the 11Li wave function contains about 30% of $(2s_{1/2})^2$ configuration.

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arXiv1999

Cluster ionization via two-plasmon excitation

We calculate the two-photon ionization of clusters for photon energies near the surface plasmon resonance. The results are expressed in terms of the ionization rate of a double plasmon excitation, which is calculated perturbatively. For the conditions of the experiment by Schlipper et al., we find an ionization rate of the order of 0.05-0.10 fs^(-1). This rate is used to determine the ionization probability in an external field in terms of the number of photons absorbed and the duration of the field. The probability also depends on the damping rate of the surface plasmon. Agreement with experiment can only be achieved if the plasmon damping is considerably smaller than its observed width in the room-temperature single-photon absorption spectrum.

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