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  • 1
    Electronic Resource
    Electronic Resource
    On the calculation of mean lifetimes in the preequilibrium exciton model (1979)
    Springer
    The European physical journal 292 (1979), S. 57-59 
    Details
    ISSN: 1434-601X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract An explicit and exact calculation method of mean lifetimes in the nuclear exciton model describing preequilibrium decay is presented. A simple algorithm is suggested. Relations of existing approaches with the analytical solution of the time-integrated master equation are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01434630
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Comments on the state densities and the transition rates in the pre-equilibrium exciton model (1985)
    Springer
    The European physical journal 321 (1985), S. 605-612 
    Details
    ISSN: 1434-601X
    Keywords: 21.10M ; 21.65 ; 25.40
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract It is proposed to renormalize the exciton-state densities used in models for precompound decay such that the summed state densities agree with the expressions employed in equilibrium statistical models. In this way a close fit can be guaranteed between preequilibrium model calculations and the results of equilibrium statistical models for the evaporative stage of the reaction. The consequences of this proposal for the internal transition rates of the pre-equilibrium exciton model are analyzed. The matrix element for the residual interaction is obtained not from a phenomenological parametrization, but from the nucleon mean free path in nuclear matter. It is demonstrated that the proposed renormalization, from one-component Fermi-gas formulas to two-fermion expressions for the state densities, leads to strongly improved agreement of the effective exciton-model values for the nucleon mean free path in nuclear matter with realistic estimates. It is proved that the particle-hole state densities for a two-component Fermi gas, summed over the allowed exciton-state numbers, agree with the phenomenological state-density expressions used in statistical Hauser-Feshbach models.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01432437
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Random-walk model of precompound decay: Dynamics and multi-particle emission (1981)
    Springer
    The European physical journal 300 (1981), S. 345-358 
    Details
    ISSN: 1434-601X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract It is demonstrated that the dynamics of precompound nuclear decay can be formulated, with regard to emission spectra as well as angular distributions, in terms of a simple random walk of the composite nuclear system. In distinction to other preequilibrium models a discrete time parameter is introduced, corresponding to the number of intranuclear interactions. This random-walk description can be employed to analytically calculate several characteristics of the equilibration process, such as the mean time to emission from an exciton state, the mean first passage time, and the attainment of isotropy. Also a simple and compact description of multi-particle emission is obtained. A necessary and sufficient condition is given for the equivalence of the random-walk and the usual exciton models. As an application some neutron emission spectra of neutron-induced reactions on127I atE=15 to 50 MeV have been calculated. The results show that preequilibrium effects are very important in the first-particle emission. In the emission of secondary particles preequilibrium effects need to be included at incoming energies above about 25 MeV. Preequilibrium effects in tertiary emission spectra are not significant belowE=50 MeV.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01419867
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Random-walk model of precompound decay II: Stochastic uncertainties in the lifetimes and cross-sections (1983)
    Springer
    The European physical journal 313 (1983), S. 83-92 
    Details
    ISSN: 1434-601X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The uncertainties arising from the stochastic nature of precompound decay nuclear reactions are analyzed in the framework of the preequilibrium exciton and random-walk models. It is demonstrated that the standard deviations and the mean values of the exciton-state lifetimes are of the same order of magnitude. Their correlations are weakly positive, except for exciton states near the equilibrium number, where the correlations are significant. The usefulness and the limitations of the never-come-back approximation are discussed. A general proof is presented of the conditions under which the master-equation and random-walk approaches to Markov processes are equivalent. Connections between different preequilibrium models, e.g. the multi-step compound model and the microscopic statistical theory of precompound decay, are pointed out. It is shown that the waiting time between subsequent collisions is governed by a Poisson process, suggesting that the variance associated with the nucleon mean free path in nuclear matter, as estimated from preequilibrium models, is considerable. The stochastic uncertainties in the emission cross-sections correspond to those of a Bernoulli process.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02115845
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    Paper (German National Licenses)
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