Navegando por Autor "Hussein, Mahir Saleh"

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Addendum : attenuation of the intensity within a superdeformed band.
(2004) Sargeant, Adam James; Hussein, Mahir Saleh; Pato, Mauricio Porto; Takigawa, Noboru; Ueda, Masahito
We investigate a random matrix model [Phys. Rev. C 65, 024302 (2002)] for the decay-out of a superdeformed band as a function of the parameters: G# /GS, GN/D, GS /D, and D/D. Here G# is the spreading width for the mixing of a superdeformed (SD) state u0l with a normally deformed (ND) doorway state udl, GS and GN are the electromagnetic widths of the SD and ND states, respectively, D is the mean level spacing of the compound ND states and D is the energy difference between u0l and udl. The maximum possible effect of a transition from ordered to chaotic states 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 a transition from ordered to chaotic states.
Attenuation of the intensity within a superdeformed band.
(2001) Sargeant, Adam James; Hussein, Mahir Saleh; Pato, Mauricio Porto; Takigawa, Noboru; Ueda, Masahito
The attenuation of the intra-band intensity of a superdeformed band which results from mixing with normally deformed configurations is calculated using reaction theory. It is found that the sharp increase of the attenuation is mostly due to the tunnelling through a spin dependent barrier and not to the chaotic nature of the normally deformed states.
Effective astrophysical S factor for nonresonant reactions.
(2000) Ueda, Masahito; Sargeant, Adam James; Pato, Mauricio Porto; Hussein, Mahir Saleh
We have made an asymptotic expansion of the effective S factor, Seff , for nonresonant reactions of charged particles. The resulting analytic formulas can generate approximations to Seff which contain derivatives, with respect to the center of mass energy E, of the astrophysical S factor, S(E), up to any desired order. Thus our approximation incorporates better the center-of-mass energy dependence in S(E) than previous approximations which included only the first or second derivatives. The range of applicability of the method is discussed. We numerically investigate our expressions for the reaction 7Be(p,g )8B.
Energy averages and fluctuations in the decay out of superdeformed bands.
(2002) Sargeant, Adam James; Hussein, Mahir Saleh; Pato, Mauricio Porto; Ueda, Masahito
We derive analytic formulas for the energy average including the energy average of the fluctuation contribution! and variance of the intraband decay intensity of a superdeformed band. Our results may be expressed in terms of three dimensionless variables: G#/GS , GN /d, and GN /(GS1G#). Here G# is the spreading width for the mixing of a superdeformed ~SD! state u0& with the normally deformed ~ND! states uQ& whose spin is the same as u0&’s. The uQ& have mean lever spacing d and mean electromagnetic decay width GN whilst u0& has electromagnetic decay width GS. The average decay intensity may be expressed solely in terms of the variables G#/GS and GN /d or, analogously to statistical nuclear reaction theory, in terms of the transmission coefficients T0(E) and TN describing transmission from the uQ& to the SD band via u0& and to lower ND states. The variance of the decay intensity, in analogy with Ericson’s theory of cross section fluctuations, depends on an additional variable, the correlation length GN /(GS1G#)5(d/2p)TN /(GS1G#). This suggests that analysis of an experimentally determined variance could yield the mean level spacing d as does analysis of the cross section autocorrelation function in compound nucleus reactions. We compare our results with those of Gu and Weidenmu¨ller.
Evaluation of effective astrophysical S factor for non-resonant reactions.
(2001) Ueda, Masahito; Sargeant, Adam James; Pato, Mauricio Porto; Hussein, Mahir Saleh
We derived analytic formulas of the effective astrophysical S factor, Seff, for a non- resonant reaction of charged particles using a Taylor expansion of the astrophysical S factor, S(E), and a uniform approximation. The formulas will be able to generate more accurate approximations to Seff than previous ones.
How large is the spreading width of a superdeformed band?
(2005) Wilson, Andrew Norman; Sargeant, Adam James; Davidson, Peter Michael; Hussein, Mahir Saleh
Recent models of the decay out of superdeformed (SD) bands can broadly be divided into two categories. One approach is based on the similarity between the tunneling process involved in the decay and that involved in the fusion of heavy ions, and it builds on the formalism of nuclear reaction theory. The other arises from an analogy between the superdeformed decay and transport between coupled quantum dots. These models suggest conflicting values for the spreading width of the decaying superdeformed states. In this paper, the decay of superdeformed bands in the five even-even nuclei in which the SD excitation energies have been determined experimentally is considered in the framework of both approaches, and the significance of the difference in the resulting spreading widths is considered. The results of the two models are also compared to tunneling widths estimated from previous barrier height predictions and a parabolic approximation to the barrier shape.
Level density for deformations of the Gaussian orthogonal ensemble.
(2005) Bertuola, Alberto Carlos; Carvalho, Josué Xavier de; Hussein, Mahir Saleh; Pato, Mauricio Porto; Sargeant, Adam James
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 sid the transition from the Gaussian orthogonal ensemble sGOEd to the Poisson ensemble and siid the transition from the GOE to m GOEs.
Perturbation treatment of symmetry breaking within random matrix theory.
(2008) Carvalho, Josué Xavier de; Hussein, Mahir Saleh; Pato, Mauricio Porto; Sargeant, Adam James
We discuss the applicability, within the random matrix theory, of perturbative treatment of symmetry breaking to the experimental data on the flip symmetry breaking in quartz crystal. We found that the values of the parameter that measures this breaking are different for the spacing distribution as compared to those for the spectral rigidity. We consider both two-fold and three-fold symmetries. The latter was found to account better for the spectral rigidity than the former. Both cases, however, underestimate the experimental spectral rigidity at large L. This discrepancy can be resolved if an appropriate number of eigenfrequencies is considered to be missing in the sample. Our findings are relevant for symmetry violation studies in general.
Resonances and the thermonuclear reaction rate.
(2004) Hussein, Mahir Saleh; Ueda, Masahito; Sargeant, Adam James; Pato, Mauricio Porto
We present an approximate analytic expression for thermonuclear reaction rate of charged particles when the cross section contains a single narrow or wide resonance described by a Breit-Wigner shape. The resulting expression is uniformly valid as the effective energy and resonance energy coalesce. We use our expressions to calculate the reaction rate for 12C(p,γ)13N.
Resonances and thermonuclear reaction rates for charged particle collisions.
(2004) Sargeant, Adam James; Pato, Mauricio Porto; Hussein, Mahir Saleh
We derive an approximate analytic expression for thermonuclear reaction rate for charged particles for the case that the cross section contains a single narrow or broad resonance described by a Breit-Wigner shape. An asymptotic series is obtained by making a Taylor series expansion which is exact at both the effective energy of the Gamow window and at the resonance energy. The resulting expression is uniformly valid as the effective energy and resonance energy coalesce or separate and as the resonance width is varied from narrow to broad. This is not true of conventional analytic approximations. We compare our uniform approximation with the exact reaction rate numerically and find it to be accurate over a large parameter range. We use our expressions to calculate the reaction rate for 12Csp,gd13N.
Saturation of the width of the strength function
(2000) Sargeant, Adam James; Hussein, Mahir Saleh; Pato, Mauricio Porto; Ueda, Masahito
The strength function of a single state ud& is studied using the deformed Gaussian orthogonal ensemble. In particular we study the dependence of the spreading width of ud& on the degree of mixing.
Symmetry-breaking study with deformed ensembles.
(2007) Carvalho, Josué Xavier de; Hussein, Mahir Saleh; Pato, Mauricio Porto; Sargeant, Adam James
A random matrix model to describe the coupling of m-fold symmetry is constructed. The particular threefold case is used to analyze data on eigenfrequencies of elastomechanical vibration of an anisotropic quartz block. It is suggested that such an experimental and theoretical study may supply a powerful means to discern the intrinsic symmetry of physical systems.
Variance of the decay intensity of superdeformed bands.
(2004) Hussein, Mahir Saleh; Sargeant, Adam James; Pato, Mauricio Porto; Ueda, Masahito
We present analytic formulae for the energy average and variance of the intraband decay intensity of a superdeformed band.