179 research outputs found
The impact of global nuclear mass model uncertainties on -process abundance predictions
Rapid neutron capture or `-process' nucleosynthesis may be responsible for
half the production of heavy elements above iron on the periodic table. Masses
are one of the most important nuclear physics ingredients that go into
calculations of -process nucleosynthesis as they enter into the calculations
of reaction rates, decay rates, branching ratios and Q-values. We explore the
impact of uncertainties in three nuclear mass models on -process abundances
by performing global monte carlo simulations. We show that root-mean-square
(rms) errors of current mass models are large so that current -process
predictions are insufficient in predicting features found in solar residuals
and in -process enhanced metal poor stars. We conclude that the reduction of
global rms errors below keV will allow for more robust -process
predictions.Comment: 5 pages, 3 figures, invited talk at the 15th International Symposium
on Capture Gamma-Ray Spectroscopy and Related Topics (CGS15), to appear in
EPJ Web of Conference
Kenneth R. Hammond’s contributions to the study of human judgment and decision making
Kenneth R. Hammond (1917–2015) made several major contributions to the science of human judgment and decision
making. As a student of Egon Brunswik, he kept Brunswik’s legacy alive – advancing his theory of probabilistic functionalism and championing his method of representative design. Hammond pioneered the use of Brunswik’s lens model as a framework for studying how individuals use information from the task environment to make clinical judgments, which was the precursor to much ‘policy capturing’ and ‘judgment analysis’ research. Hammond introduced the lens model equation to the study of judgment processes, and used this to measure the utility of different forms of feedback in multiple-cue probability learning. He extended the scope of analysis to contexts in which individuals interact with one another – introducing the interpersonal learning and interpersonal conflict paradigms. Hammond developed social judgment theory which provided a comprehensive quantitative approach for describing and improving judgment processes. He proposed cognitive continuum theory which states that quasi-rationality is an important middle-ground between intuition and analysis and that cognitive performance is dictated by the match between task properties and mode of cognition. Throughout his career, Hammond moved easily from basic laboratory work to applied settings, where he resolved policy disputes, and in doing so, he pointed to the dichotomy between theories of correspondence and coherence. In this paper, we present Hammond’s legacy to a new generation of judgment and decision making scholars
The sensitivity of r-process nucleosynthesis to the properties of neutron-rich nuclei
About half of the heavy elements in the Solar System were created by rapid
neutron capture, or r-process, nucleosynthesis. In the r-process, heavy
elements are built up via a sequence of neutron captures and beta decays in
which an intense neutron flux pushes material out towards the neutron drip
line. The nuclear network simulations used to test potential astrophysical
scenarios for the r-process therefore require nuclear physics data (masses,
beta decay lifetimes, neutron capture rates, fission probabilities) for
thousands of nuclei far from stability. Only a small fraction of this data has
been experimentally measured. Here we discuss recent sensitivity studies that
aim to determine the nuclei whose properties are most crucial for r-process
calculations.Comment: 8 pages, 4 figures, submitted to the Proceedings of the Fifth
International Conference on Fission and Properties of Neutron-Rich Nuclei
(ICFN5
Sensitivity studies for r-process nucleosynthesis in three astrophysical scenarios
In rapid neutron capture, or r-process, nucleosynthesis, heavy elements are
built up via a sequence of neutron captures and beta decays that involves
thousands of nuclei far from stability. Though we understand the basics of how
the r-process proceeds, its astrophysical site is still not conclusively known.
The nuclear network simulations we use to test potential astrophysical
scenarios require nuclear physics data (masses, beta decay lifetimes, neutron
capture rates, fission probabilities) for all of the nuclei on the neutron-rich
side of the nuclear chart, from the valley of stability to the neutron drip
line. Here we discuss recent sensitivity studies that aim to determine which
individual pieces of nuclear data are the most crucial for r-process
calculations. We consider three types of astrophysical scenarios: a traditional
hot r-process, a cold r-process in which the temperature and density drop
rapidly, and a neutron star merger trajectory.Comment: 8 pages, 4 figures, submitted to the Proceedings of the International
Nuclear Physics Conference (INPC) 201
The Influence Of Neutron Capture Rates On The Rare Earth Region Of The r-Process Abundance Pattern
We study the sensitivity of the r-process abundance pattern to neutron
capture rates along the rare earth region (A~150 to A~180). We introduce the
concepts of large nuclear flow and flow saturation which determine the neutron
capture rates that are influential in setting the rare earth abundances. We
illustrate the value of the two concepts by considering high entropy conditions
favorable for rare earth peak production and identifying important neutron
capture rates among the rare earth isotopes. We also show how these rates
influence nuclear flow and specific sections of the abundance pattern.Comment: 14 pages, 7 figures, submitted to PR
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