282 research outputs found
Isotopic Scaling of Heavy Projectile Residues from the collisions of 25 MeV/nucleon 86Kr with 124Sn, 112Sn and 64Ni, 58Ni
The scaling of the yields of heavy projectile residues from the reactions of
25 MeV/nucleon 86Kr projectiles with 124Sn,112Sn and 64Ni, 58Nitargets is
studied. Isotopically resolved yield distributions of projectile fragments in
the range Z=10-36 from these reaction pairs were measured with the MARS recoil
separator in the angular range 2.7-5.3 degrees. The velocities of the residues,
monotonically decreasing with Z down to Z~26-28, are employed to characterize
the excitation energy. The yield ratios R21(N,Z) for each pair of systems are
found to exhibit isotopic scaling (isoscaling), namely, an exponential
dependence on the fragment atomic number Z and neutron number N. The isoscaling
is found to occur in the residue Z range corresponding to the maximum observed
excitation energies. The corresponding isoscaling parameters are alpha=0.43 and
beta=-0.50 for the Kr+Sn system and alpha=0.27 and beta=-0.34 for the Kr+Ni
system. For the Kr+Sn system, for which the experimental angular acceptance
range lies inside the grazing angle, isoscaling was found to occur for Z<26 and
N<34. For heavier fragments from Kr+Sn, the parameters vary monotonically,
alpha decreasing with Z and beta increasing with N. This variation is found to
be related to the evolution towards isospin equilibration and, as such, it can
serve as a tracer of the N/Z equilibration process. The present heavy-residue
data extend the observation of isotopic scaling from the intermediate mass
fragment region to the heavy-residue region. Such high-resolution mass
spectrometric data can provide important information on the role of isospin in
peripheral and mid-peripheral collisions, complementary to that accessible from
modern large-acceptance multidetector devices.Comment: 8 pages, 6 figures, submitted to Phys. Rev.
Neutron-rich rare isotope production from projectile fission of heavy beams in the energy range of 20 MeV/nucleon
We investigate the possibilities of producing neutron-rich nuclides in
projectile fission of heavy beams in the energy range of 20 MeV/nucleon
expected from low-energy facilities. We report our efforts to theoretically
describe the reaction mechanism of projectile fission following a multinucleon
transfer collision at this energy range. Our calculations are mainly based on a
two-step approach: the dynamical stage of the collision is described with
either the phenomenological Deep-Inelastic Transfer model (DIT), or with the
microscopic Constrained Molecular Dynamics model (CoMD). The
deexcitation/fission of the hot heavy projectile fragments is performed with
the Statistical Mul- tifragmentation Model (SMM). We compared our model
calculations with our previous experimental projectile-fission data of 238U (20
MeV/nucleon)+208Pb and 197Au (20 MeV/nucleon)+197Au and found an overall
reasonable agreement. Our study suggests that projectile fission following
periph- eral heavy-ion collisions at this energy range offers an effective
route to access very neutron-rich rare isotopes toward and beyond the
astrophysical r-process path
Heavy Residue Formation in 20 MeV/nucleon 197Au + 90Zr collisions
The yields and velocity distributions of heavy residues and fission fragments
from the reaction of 20 MeV/nucleon 197Au + 90Zr have been measured using the
MSU A1200 fragment separator. A bimodal distribution of residues is observed,
with one group, resulting from peripheral collisions, having fragment mass
numbers A=160-200, while the other group, resulting from ``hard'' collisions,
has A=120-160. This latter group of residues can be distinguished from fission
fragments by their lower velocities. A model combining deep-inelastic transfer
and incomplete fusion for the primary interaction stage and a statistical
evaporation code for the deexcitation stage has been used to describe the
properties of the product distributions.Comment: 19 pages, 6 figures, preprint submitted to Nucl. Phys.
Timescale for equilibration of N/Z gradients in dinuclear systems
Equilibration of N/Z in binary breakup of an excited and transiently deformed
projectile-like fragment (PLF*), produced in peripheral collisions of 64Zn +
27Al, 64Zn, 209Bi at E/A = 45 MeV, is examined. The composition of emitted
light fragments (3<=Z<=6) changes with the decay angle of the PLF*. The most
neutron-rich fragments observed are associated with a small rotation angle. A
clear target dependence is observed with the largest initial N/Z correlated
with the heavy, neutron-rich target. Using the rotation angle as a clock, we
deduce that N/Z equilibration persists for times as long as 3-4 zs (1zs = 1 x
10^-21 s = 300 fm/c). The rate of N/Z equilibration is found to depend on the
initial neutron gradient within the PLF*.Comment: 6 pages, 4 figure
Analysis of fragment yield ratios in the nuclear phase transition
The critical phenomena of the liquid-gas phase transition has been
investigated in the reactions 78,86Kr+58,64Ni at beam energy of 35 MeV/nucleon
using the Landau free energy approach with isospin asymmetry as an order
parameter. Fits to the free energy of fragments showed three minima suggesting
the system to be in the regime of a first order phase transition. The relation
m =-{\partial}F/{\partial}H, which defines the order parameter and its
conjugate field H, has been experimentally verified from the linear dependence
of the mirror nuclei yield ratio data, on the isospin asymmetry of the source.
The slope parameter, which is a measure of the distance from a critical
temperature, showed a systematic decrease with increasing excitation energy of
the source. Within the framework of the Landau free energy approach, isoscaling
provided similar results as obtained from the analysis of mirror nuclei yield
ratio data. We show that the external field is primarily related to the minimum
of the free energy, which implies a modification of the source concentration
\Delta used in isospin studies
Integrated primary health care in Greece, a missing issue in the current health policy agenda: a systematic review
Background: Over the past years, Greece has undergone several endeavors aimed at modernizing and improving national health care services with a focus on PHC. However, the extent to which integrated primary health care has been achieved is still questioned. <br><br> Purpose: This paper explores the extent to which integrated primary health care (PHC) is an issue in the current agenda of policy makers in Greece, reporting constraints and opportunities and highlighting the need for a policy perspective in developing integrated PHC in this Southern European country. <br><br> Methods: A systematic review in PubMed/Medline and SCOPUS, along with a hand search in selected Greek biomedical journals was undertaken to identify key papers, reports, editorials or opinion letters relevant to integrated health care. <br><br> Results: Our systematic review identified 198 papers and 161 out of them were derived from electronic search. Fifty-three papers in total served the scope of this review and are shortly reported. A key finding is that the long-standing dominance of medical perspectives in Greek health policy has been paving the way towards vertical integration, pushing aside any discussions about horizontal or comprehensive integration of care. <br><br> Conclusion: Establishment of integrated PHC in Greece is still at its infancy, requiring major restructuring of the current national health system, as well as organizational culture changes. Moving towards a new policy-based model would bring this missing issue on the discussion table, facilitating further development
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