725 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
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]
Particle-hole state densities with non-equidistant single-particle levels
The correct use of energy-dependent single-particle level (s.p.l.) densities
within particle-hole state densities based on the equidistant spacing model
(ESM) is analysed. First, an analytical expression is obtained following the
convolution of energy-dependent excited-particle and hole densities. Next, a
comparison is made with results of the ESM formula using average s.p.l.
densities for the excited particles and holes, respectively. The Fermi-gas
model (FGM) s.p.l. densities calculated at the corresponding average excitation
energies are used in both cases. The analysis concerns also the density of
particle-hole bound states. The pairing correlations are taken into account
while the comparison of various effects includes the exact correction for the
Pauli exclusion principle. Quantum-mechanical s.p.l. densities and the
continuum effect can also match a corresponding FGM formula, suitable for use
within the average energy-dependent partial state density in multistep reaction
models.Comment: 29 pages, ReVTeX, 11 postscript figures, submitted to Phys.Rev.
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