573 research outputs found

### Isospin dependence of nucleon Correlations in ground state nuclei

The dispersive optical model (DOM) as presently implemented can investigate
the isospin (nucleon asymmetry) dependence of the Hartree-Fock-like potential
relevant for nucleons near the Fermi energy. Data constraints indicate that a
Lane-type potential adequately describes its asymmetry dependence. Correlations
beyond the mean-field can also be described in this framework, but this
requires an extension that treats the non-locality of the Hartree-Fock-like
potential properly. The DOM has therefore been extended to properly describe
ground-state properties of nuclei as a function of nucleon asymmetry in
addition to standard ingredients like elastic nucleon scattering data and level
structure. Predictions of nucleon correlations at larger nucleon asymmetries
can then be made after data at smaller asymmetries constrain the potentials
that represent the nucleon self-energy. A simple extrapolation for Sn isotopes
generates predictions for increasing correlations of minority protons with
increasing neutron number. Such predictions can be investigated by performing
experiments with exotic beams. The predicted neutron properties for the double
closed-shell 132Sn nucleus exhibit similar correlations as those in 208Pb.
Future relevance of these studies for understanding the properties of all
nucleons, including those with high momentum, and the role of three-body forces
in nuclei are briefly discussed. Such an implementation will require a proper
treatment of the non-locality of the imaginary part of the potentials and a
description of high-momentum nucleons as experimentally constrained by the
(e,e'p) reactions performed at Jefferson Lab.Comment: 7 pages and 7 figure

### Simulations of collisions between nuclei at intermediate energy using the Boltzmann-Uehling- Uhlenbeck equation with neutron skin producing potentials

Asymmetry dependent potentials, which produce neutron skins, are utilized in the Boltzmann-UehlingUhlenbeck equation in order to simulate intermediate energy heavy-ion collisions. Compared to calculations done with the commonly used equation of states, the calculations which use the asymmetry dependent potentials produce neutron rich neck regions which reduces the orbiting of the major fragments and can produce primary, neutron rich, intermediate velocity ("neck") fragments. PACS number(s): 25.70. Pq, 25.70.Lm, One of the main goals of heavy-ion nuclear physics is to study the nuclear matter equation of state (EOS). Aside from finite particle effects, one is forced to address the question of what can be extracted about the equilibrium properties of the matter from the collision dynamics. This has lead to the development of reaction models which incorporate nuclear matter properties with an assumption of local equilibrium as well as assumptions about the in-medium nucleon-nucleon cross section. It is the hope that by comparison of such models to experimental data that insight can be gained into the nuclear matter EOS. Some of the important models in this endeavor (and cental to the present work) are those which solve the Boltzmann-Uehling-Uhlenbeck (BUU) equation The enhancement of the neutron density, relative to the proton density, with decreasing overall density (increasing =r+ (P +bP P +P )+~(P P +P P ) PO PO In the above expression,~represents the kinetic energy and the neutron potential (bottom) as functions of the asymmetry for three different values of the total density. This potential is labeled "ISO-STIFF. " It is important to note that the asymmetry stiffness decreases with decreasing overall density. This is the feature which is required to produce reasonable neutron skins. The unmodified Skyrme interaction does not directly provide insight into a form for a "SOFT" asymmetry dependent potential (K=200 MeV). The ad hoc solution used in the present work is to paste the asymmetry dependence of the "ISO-STIFF" EOS onto the density dependence of the standard "SOFI"' EOS, U(p) = n, (p/p, )+ P,(p/p, ) / . The effect of the "ISO-SOFT" potential can then be thought of as producing an asymmetry force of magnitude equal to the difference between the slope of the potential (se

### Asymmetry dependence of proton correlations

A dispersive optical model analysis of p+40Ca and p+48Ca interactions has
been carried out. The real and imaginary potentials have been constrained from
fits to elastic scattering data, reaction cross sections, and level properties
of valence hole states deduced from (e,e'p) data. The surface imaginary
potential was found to be larger overall and the gap in this potential on
either side of the Fermi energy was found to be smaller for the neutron-rich
p+48Ca system. These results imply that protons with energies near the Fermi
surface experience larger correlations with increasing asymmetry.Comment: 4 pages, 5 figure

### Retardation of Particle Evaporation from Excited Nuclear Systems Due to Thermal Expansion

Particle evaporation rates from excited nuclear systems at equilibrium matter
density are studied within the Harmonic-Interaction Fermi Gas Model (HIFGM)
combined with Weisskopf's detailed balance approach. It is found that thermal
expansion of a hot nucleus, as described quantitatively by HIFGM, leads to a
significant retardation of particle emission, greatly extending the validity of
Weisskopf's approach. The decay of such highly excited nuclei is strongly
influenced by surface instabilities

### Tidal effects and the Proximity decay of nuclei

We examine the decay of the 3.03 MeV state of $^8$Be evaporated from an
excited projectile-like fragment following a peripheral heavy-ion collision.
The relative energy of the daughter $\alpha$ particles exhibits a dependence on
the decay angle of the $^8$Be$^*$, indicative of a tidal effect. Comparison of
the measured tidal effect with a purely Coulomb model suggests the influence of
a measurable nuclear proximity interaction.Comment: 5 pages, 4 figure

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### Fast-Particle Emission as a Probe of the Energy Dissipation Mechanism in Deep-Inelastic Reactions

### Neutron and Proton Transverse Emission Ratio Measurements and the Density Dependence of the Asymmetry Term of the Nuclear Equation of State

Recent measurements of pre-equilibrium neutron and proton transverse emission
from (112,124)Sn+(112,124)Sn reactions at 50 MeV/A have been completed at the
National Superconducting Cyclotron Laboratory. Free nucleon transverse emission
ratios are compared to those of A=3 mirror nuclei. Comparisons are made to BUU
transport calculations and conclusions concerning the density dependence of the
asymmetry term of the nuclear equation-of-state at sub-nuclear densities are
made. The double-ratio of neutron-proton ratios between two reactions is
employed as a means of reducing first-order Coulomb effects and detector
efficiency effects. Comparison to BUU model predictions indicate a density
dependence of the asymmetry energy that is closer to a form in which the
asymmety energy increases as the square root of the density for the density
region studied. A coalescent-invariant analysis is introduced as a means of
reducing suggested difficulties with cluster emission in total nucleon
emission. Future experimentation is presented

### Three-body decay of $^{6}$Be

Three-body correlations for the ground-state decay of the lightest two-proton
emitter $^{6}$Be are studied both theoretically and experimentally. Theoretical
studies are performed in a three-body hyperspherical-harmonics cluster model.
In the experimental studies, the ground state of $^{6}$Be was formed following
the $\alpha$ decay of a $^{10}$C beam inelastically excited through
interactions with Be and C targets. Excellent agreement between theory and
experiment is obtained demonstrating the existence of complicated correlation
patterns which can elucidate the structure of $^{6}$Be and, possibly, of the
A=6 isobar.Comment: 17 pages, 21 figures, 5 table

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