222 research outputs found
The Role of Fission in Neutron Star Mergers and Its Impact on the r-Process Peaks
Comparing observational abundance features with nucleosynthesis predictions of stellar evolution or explosion simulations, we can scrutinize two aspects: (a) the conditions in the astrophysical production site and (b) the quality of the nuclear physics input utilized. We test the abundance features of r-process nucleosynthesis calculations for the dynamical ejecta of neutron star merger simulations based on three different nuclear mass models: The Finite Range Droplet Model, the (quenched version of the) Extended Thomas Fermi Model with Strutinsky Integral, and the Hartree-Fock-Bogoliubov mass model. We make use of corresponding fission barrier heights and compare the impact of four different fission fragment distribution models on the final r-process abundance distribution. In particular, we explore the abundance distribution in the second r-process peak and the rare-earth sub-peak as a function of mass models and fission fragment distributions, as well as the origin of a shift in the third r-process peak position. The latter has been noticed in a number of merger nucleosynthesis predictions. We show that the shift occurs during the r-process freeze-out when neutron captures and β-decays compete and an (n,γ)-(γ,n) equilibrium is no longer maintained. During this phase neutrons originate mainly from fission of material above A = 240. We also investigate the role of β-decay half-lives from recent theoretical advances, which lead either to a smaller amount of fissioning nuclei during freeze-out or a faster (and thus earlier) release of fission neutrons, which can (partially) prevent this shift and has an impact on the second and rare-earth peak as well.Peer reviewe
Isotopic and velocity distributions of Bi produced in charge-pickup reactions of 208Pb at 1 A GeV
Isotopically resolved cross sections and velocity distributions have been
measured in charge-pickup reactions of 1 A GeV 208Pb with proton, deuterium and
titanium target. The total and partial charge-pickup cross sections in the
reactions 208Pb + 1H and 208Pb + 2H are measured to be the same in the limits
of the error bars. A weak increase in the total charge-pickup cross section is
seen in the reaction of 208Pb with the titanium target. The measured velocity
distributions show different contributions - quasi-elastic scattering and
Delta-resonance excitation - to the charge-pickup production. Data on total and
partial charge-pickup cross sections from these three reactions are compared
with other existing data and also with model calculations based on the coupling
of different intra-nuclear cascade codes and an evaporation code.Comment: 20 pages, 12 figures, background information on
http://www-w2k.gsi.de/kschmidt
Measuring the Temperature of Hot Nuclear Fragments
A new thermometer based on fragment momentum fluctuations is presented. This
thermometer exhibited residual contamination from the collective motion of the
fragments along the beam axis. For this reason, the transverse direction has
been explored. Additionally, a mass dependence was observed for this
thermometer. This mass dependence may be the result of the Fermi momentum of
nucleons or the different properties of the fragments (binding energy, spin
etc..) which might be more sensitive to different densities and temperatures of
the exploding fragments. We expect some of these aspects to be smaller for
protons (and/or neutrons); consequently, the proton transverse momentum
fluctuations were used to investigate the temperature dependence of the source
Production of medium-mass neutron-rich nuclei in reactions induced by 136Xe projectiles at 1 A GeV on a beryllium target
Production cross sections of medium-mass neutron-rich nuclei obtained in the
fragmentation of 136Xe projectiles at 1 A GeV have been measured with the
FRagment Separator (FRS) at GSI. 125Pd was identified for the first time. The
measured cross sections are compared to 238U fission yields and model
calculations in order to determine the optimum reaction mechanism to extend the
limits of the chart of the nuclides around the r-process waiting point at N=82.Comment: 9 pages, 6 figure
Asymmetry Dependence of the Nuclear Caloric Curve
A basic feature of the nuclear equation of state is not yet understood: the
dependence of the nuclear caloric curve on the neutron-proton asymmetry.
Predictions of theoretical models differ on the magnitude and even the sign of
this dependence. In this work, the nuclear caloric curve is examined for fully
reconstructed quasi-projectiles around mass A=50. The caloric curve extracted
with the momentum quadrupole fluctuation thermometer shows that the temperature
varies linearly with quasi-projectile asymmetry (N-Z)/A. An increase in
asymmetry of 0.15 units corresponds to a decrease in temperature on the order
of 1 MeV. These results also highlight the importance of a full
quasi-projectile reconstruction in the study of thermodynamic properties of hot
nuclei
INCL4.5 and Abla07 - Improved versions of the intranuclear cascade (INCL4) and deexcitation (Abla) models
peer reviewe
Fundamental Concepts of Cyber Resilience: Introduction and Overview
Given the rapid evolution of threats to cyber systems, new management
approaches are needed that address risk across all interdependent domains
(i.e., physical, information, cognitive, and social) of cyber systems. Further,
the traditional approach of hardening of cyber systems against identified
threats has proven to be impossible. Therefore, in the same way that biological
systems develop immunity as a way to respond to infections and other attacks,
so too must cyber systems adapt to ever-changing threats that continue to
attack vital system functions, and to bounce back from the effects of the
attacks. Here, we explain the basic concepts of resilience in the context of
systems, discuss related properties, and make business case of cyber
resilience. We also offer a brief summary of ways to assess cyber resilience of
a system, and approaches to improving cyber resilience.Comment: This is a preprint version of a chapter that appears in the book
"Cyber Resilience of Systems and Networks," Springer 201
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