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M. S. Hussein

Publications and source records attributed to M. S. Hussein.

At least 91 records · Page 5Linked to original sources
arXiv2006

Elastic Scattering and Total Reaction Cross Section for the 6He + 27Al System

The elastic scattering of the radioactive halo nucleus 6He on 27Al target was measured at four energies close to the Coulomb barrier using the RIBRAS (Radioactive Ion Beams in Brazil) facility. The Sao Paulo Potential(SPP) was used and its diffuseness and imaginary strength were adjusted to fit the elastic scattering angular distributions. Reaction cross-sections were extracted from the optical model fits. The reduced reaction cross-sections of 6He on 27Al are similar to those for stable, weakly bound projectiles as {6,7}Li, 9Be and larger than stable, tightly bound projectile as 16O on 27Al.

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arXiv2006

Low energy transfer cross-section for Borromean halo nuclei

We describe a schematic coupled channels transfer calculation for the reaction 6He + 238U at near-barrier energies. We also present a simple semiclassical DWBA calculation of the two neutron transfer. Both calculations are meant to supply the conditions under which the transfer cross section becomes much larger than the complete fusion one at sub-barrier energies. It seems that a feasible mechanism is the incoherent contributions of two or more processes with quite different Q-vlaues.

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arXiv2006

Scaling and Interference in the Dissociation of Halo Nuclei

The dissociation of halo nuclei through their collision with light and heavy targets is considered within the Continuum Discretized Coupled Channels theory. We study the one-proton halo nucleus $^8$B and the one-neutron halo nucleus $^{11}$Be, as well as the more normal $^7$Be. The procedure previously employed to extract the Coulomb dissociation cross section by subtracting the nuclear one is critically assessed, and the scaling law usually assumed for the target mass dependence of the nuclear breakup cross section is also tested. It is found that the nuclear breakup cross section for these very loosely bound nuclei does indeed behave as $a+bA^{1/3}$. However, it does not have the geometrically inspired form of a circular ring which seems to be the case for normal nuclei such as $^{7}$Be. We find further that we cannot ignore Coulomb-nuclear interference effects, which may be constructive or destructive in nature, and so the errors in previously extracted B(E1) using the subtraction procedure are almost certainly underestimated.

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arXiv2006

A doorway to Borromean halo nuclei: the Samba configuration

We exploit the possibility of new configurations in three-body halo nuclei - Samba type - (the neutron-core form a bound system) as a doorway to Borromean systems. The nuclei $^{12}$Be, $^{15}$B, $^{23}$N and $^{27}$F are of such nature, in particular $^{23}$N with a half-life of 37.7 s and a halo radius of 6.07 fm is an excellent example of Samba-halo configuration. The fusion below the barrier of the Samba halo nuclei with heavy targets could reveal the so far elusive enhancement and a dominance of one-neutron over two-neutron transfers, in contrast to what was found recently for the Borromean halo nucleus $^6$He + $^{238}$U.

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arXiv2005

The Semiclassical Coulomb Interaction

The semiclassical Coulomb excitation interaction is at times expressed in the Lorentz gauge in terms of the electromagnetic fields and a contribution from the scalar electric potential. We point out that the potential term can make spurious contributions to excitation cross sections, especially when the the decay of excited states is taken into account. We show that, through an appropriate gauge transformation, the excitation interaction can be expressed in terms of the electromagnetic fields alone.

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arXiv2005

Level density for deformations of the Gaussian orthogonal ensemble

Formulas are derived for the average level density of deformed, or transition, Gaussian orthogonal random matrix ensembles. After some general considerations about Gaussian ensembles we derive formulas for the average level density for (i) the transition from the Gaussian orthogonal ensemble (GOE) to the Poisson ensemble and (ii) the transition from the GOE to $m$ GOEs.

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arXiv2005

Multi-level and two-level models of the decay out of superdeformed bands

We compare a multi-level statistical model with a two-level model for the decay out of superdeformed rotational bands in atomic nuclei. We conclude that while the models depend on different dimensionless combinations of the input parameters and differ in certain limits, they essentially agree in the cases where experimental data is currently available. The implications of this conclusion are discussed.

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arXiv2005

Effect of the break-up on the fusion and elastic scattering of weakly bound projectiles on $^{64}$Zn

We study the behavior of the fusion, break-up, reaction and elastic scattering of different projectiles on $^{64}$Zn, at near and above barrier energies. We present fusion and elastic scattering data with the tightly bound $^{16}$O and the stable weakly bound $^{6}$Li, $^{7}$Li and $^{9}$Be projectiles. The data were analyzed by coupled channel calculations. The total fusion cross sections for these systems are not affected by the break-up process at energies above the barrier. The elastic (non-capture) break-up cross section is important at energies close and above the Coulomb barrier and increases the reaction cross sections. In addition we also show that the break-up process at near and sub-barrier energies is responsible for the vanishing of the usual threshold anomaly of the optical potential and give rise to a new type of anomaly.

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arXiv2005

Study of the effects of Pauli blocking and Pauli non-locality on the optical potential

Elastic scattering angular distributions for systems with reduced mass between 3 and 34 and energies varying between 25 and 120 MeV/nucleon were analyzed. The stable $^4$He, its exotic partner $^6$He, and the weakly bound $^{6,7}$Li nuclei were included as projectiles in the systematics. Optical model data analyzes were performed with an adjustable factor of normalization included in the imaginary part of the potential. These analyzes indicated a reduction of absorption for systems with small reduced masses that was detected due to the refractive nature of the scattering by light systems.

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arXiv2004

Interference effects in the Coulomb dissociation of 15,17,19C

In this work the semiclassical model of pure Coulomb excitation was applied to the breakup of 15,17,19C. The ground state wave functions were calculated in the particle-rotor model including core excitation. The importance of interference terms in the dipole strength arising after including core degrees of freedom is analyzed for each isotope. It is shown that Coulomb interference effects are important for the case of 17C.

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arXiv2004

A Semiclassical Approach to Fusion Reactions

The semiclassical method of Alder and Winther is generalized to study fusion reactions. As an illustration, we evaluate the fusion cross section in a schematic two-channel calculation. The results are shown to be in good agreement with those obtained with a quantal Coupled-Channels calculation. We suggest that in the case of coupling to continuum states this approach may provide a simpler alternative to the Continuum Discretized Coupled-Channels method.

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arXiv2004

Addendum: Attenuation of the intensity within a superdeformed band

We investigate a random matrix model [Phys. Rev. C {\bf 65} 024302 (2002] for the decay-out of a superdeformed band as a function of the parameters: $Γ^\downarrow/Γ_S$, $Γ_N/D$, $Γ_S/D$ and $Δ/D$. Here $Γ^\downarrow$ is the spreading width for the mixing of an SD state $|0>$ with a normally deformed (ND) doorway state $|d>$, $Γ_S$ and $Γ_N$ are the electromagnetic widths of the the SD and ND states respectively, $D$ is the mean level spacing of the compound ND states and $Δ$ is the energy difference between $|0>$ and $|d>$. The maximum possible effect of an order-chaos transition is inferred from analytical and numerical calculations of the decay intensity in the limiting cases for which the ND states obey Poisson and GOE statistics. Our results show that the sharp attenuation of the decay intensity cannot be explained solely by an order-chaos transition.

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arXiv2004

Energy averages over regular and chaotic states in the decay out of superdeformed bands

We describe the decay out of a superdeformed band using the methods of reaction theory. Assuming that decay-out occurs due to equal coupling (on average) to a sea of equivalent chaotic normally deformed (ND) states, we calculate the average intraband decay intensity and show that it can be written as an ``optical'' background term plus a fluctuation term, in total analogy with average nuclear cross sections. We also calculate the variance in closed form. We investigate how these objects are modified when the decay to the ND states occurs via an ND doorway and the ND states' statistical properties are changed from chaotic to regular. We show that the average decay intensity depends on two dimensionless variables in the first case while in the second case, four variables enter the picture.

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arXiv2003

Molecular Signatures in Hybrid Atomic/Molecular Bose-Einstein Condensates

As it was proposed and recently verified experimentally, the mechanism of Feshbach resonance in a condensate can create a second condensate component of molecules that coexists with the atomic condensate. In this work we investigate signatures of the presence of the molecular condensate through the equilibrium properties and collective excitations of the hybrid system of atoms and molecules, subjected to a trap, employing a time-dependent variational ansatz. We show that the shape of the condensate changes significantly by the presence of the molecules and that modes unique to this hybrid system appear at observable frequencies.

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arXiv2003

Multiple giant resonances in nuclei: their excitation and decay

The excitation of multiphonon giant resonances with heavy ions is discussed. The conventional theory, based on the use of the virtual photon number method in conjunction with the harmonic model is presented and its shortcomings are discussed. The recently developed model that invoke the Brink-Axel mechanism as an important contribution to the cross-section is discussed and compared to the conventional, harmonic model. The decay properties of these multiple giant resonances are also discussed within the same coherent + fluctuation model in conjunction with the hybrid decay model. It is demonstrated that the Brink-Axel mechanism enhances the direct decay of the states, as data seem to require. Comparison of our model with other recent theoretical works is presented.

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