880 research outputs found
Expectations of fragment decay from highly excited nuclei
The statistical model is used to illustrate the consequences of a successive binary decay mechanism as the initial nuclear excitation is pushed towards the limits of stability. The partition of the excitation energy between light and heavy fragments is explicitly calculated, as are the consequences of the decay of the primary light fragments to particle-bound residual nuclei which would be observed experimentally. The test nucleus 100 44 Ru is considered at initial excitations of 100, 200, 400, and 800 MeV. Exit channels of n, p, and α; and 100 clusters of 3 †Z †20 †4, 6 †A †48 are considered from all nuclides in the deexcitation cascade. The total primary and final cluster yields are shown versus Z and initial excitation. The primary versus final yields are also shown individually for 12C, 26Mg, and 48Ca. We show how multifragmentation yields will change with the excitation energy due to a successive binary decay mechanism. Measurements that may be prone to misinterpretation are discussed, as are those that should be representative of initial nucleus excitation
Dynamical treatment of Fermi motion in a microscopic description of heavy ion collisions
A quasiclassical Pauli potential is used to simulate the Fermi motion of nucleons in a molecular dynamical simulation of heavy ion collisions. The thermostatic properties of a Fermi gas with and without interactions are presented. The inclusion of this Pauli potential into the quantum molecular dynamics (QMD) approach yields a model with well defined fermionic ground states, which is therefore also able to give the excitation energies of the emitted fragments. The deexcitation mechanisms (particle evaporation and multifragmentation) of the new model are investigated. The dynamics of the QMD with Pauli potential is tested by a wide range of comparisons of calculated and experimental double-differential cross sections for inclusive p-induced reactions at incident energies of 80 to 160 MeV. Results at 256 and 800 MeV incident proton energy are presented as predictions for completed experiments which are as yet unpublished
Implementation of GDH model in TALYS-1.7 code
The geometry dependent hybrid model proposed by M.Blann and supplied with models for the non-equilibrium cluster emission was implemented in the TALYS-1.74 code. A number of subprograms of ALICE and ALICE/ASH codes after an appropriate modification were added to TALYS. The value of the TALYS input variable preeqmode equal to five is reserved for the use of new approach. The calculated nucleon and light cluster energy distributions are compared with measured data
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Nuclear modeling applied to radioisotope production
Calculated excitation functions are provided for all proton-induced reactions listed for the Coordinated Research Program (CRP) on Development of a Reference Charge Particle Cross Section Data Base for Medical Radioisotope Production under the IAEA. The excitation functions are compared with experimental data sets as provided to the CRP. We discuss the merit of calculated results with respect to the experimental data
Investigation of soluble adhesion molecules in cancer: beneficial approach or expensive toy? The case of intercellular adhesion molecule-1 (sICAM-1)
Adhesion molecules are key topobiological components in almost any kind of cell-cell and cell-matrix interaction in both human physiology and pathology. Heterogeneous processes as platelet adhesion to subendothelial matrix components or leukocyte extravasation at sites of tissue damage are at least in part mediated by adhesion molecules and their corresponding receptors (counter receptors). Using a multitude of modem analytical and preparative approaches ranging from "simple" immunohistochemistry to cloning and gene transfer, in vitro studies provided detailed data on a variety of adhesion molecules and their receptors. However, compared to the speedy accumulation of basic knowledge the evaluation of the diagnostic usefulness of adhesion molecules is still in its infancy.Biomedical Reviews 1994; 3: 73-75
Quasiparticle Lifetime in a Finite System: A Non--Perturbative Approach
The problem of electron--electron lifetime in a quantum dot is studied beyond
perturbation theory by mapping it onto the problem of localization in the Fock
space. We identify two regimes, localized and delocalized, corresponding to
quasiparticle spectral peaks of zero and finite width, respectively. In the
localized regime, quasiparticle states are very close to single particle
excitations. In the delocalized state, each eigenstate is a superposition of
states with very different quasiparticle content. A transition between the two
regimes occurs at the energy , where is
the one particle level spacing, and is the dimensionless conductance. Near
this energy there is a broad critical region in which the states are
multifractal, and are not described by the Golden Rule.Comment: 13 pages, LaTeX, one figur
Preequilibrium Neutron Emission in (p, xn) Reactions with 80-160 MeV Projectiles
This research was sponsored by the National Science Foundation Grant NSF PHY 87-1440
Study of the nucleon-induced preequilibrium reactions in terms of the Quantum Molecular Dynamics
The preequilibrium (nucleon-in, nucleon-out) angular distributions of
Al, Ni and Zr have been analyzed in the energy region from
90 to 200 MeV in terms of the Quantum Moleculear Dynamics (QMD) theory. First,
we show that the present approach can reproduce the measured (p,xp') and (p,xn)
angular distributions leading to continuous final states without adjusing any
parameters. Second, we show the results of the detailed study of the
preequilibrium reaction processes; the step-wise contribution to the angular
distribution, comparison with the quantum-mechanical Feshbach-Kerman-Koonin
theory, the effects of momentum distribution and surface refraction/reflection
to the quasifree scattering. Finally, the present method was used to assess the
importance of multiple preequilibrium particle emission as a function of
projectile energy up to 1 GeV.Comment: 22pages, Revex is used, 10 Postscript figures are available by
request from [email protected]
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