ISNAP Research Highlights
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Fusion Reactions at the Limits of Stability |
| Nuclear reactions are at the heart of stellar structure, evolution and nucleosynthesis from main sequence, giants and super-giants to supernovae, white dwarfs and neutron stars. Depending on fuel, temperature, and density, stellar burning may involve many reactions of different nuclei, from light to heavy and stable to extremely neutron rich ones. The possibility of fusion reactions between low mass nuclei at low temperatures but extremely high densities occurs in the cores of white dwarfs and the crust of neutron stars. In white dwarf matter the 12C+12C fusion may trigger type I supernovae, in neutron star crusts fusion between very neutron rich nuclei may provide internal heating.
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A Jet-Gastarget for the St. George
recoil mass separator |
| The recoil mass separator St. George at Notre Dame is primarily designed to study alpha capture reactions in inverse kinematics. Therefore a heavy ion beam is in combination with a 4He gas target. We designed a differentially pumped windowless jet-gas target to reduce beam straggling and back ground scattering and provide a point-like source for the recoil separator.
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a-Capture
Measurements on p-Nuclei |
| Abundance calculations
for the p-nuclei involve an extended network of about 20,000 nuclear
reactions of almost 2000 nuclei with masses ranging from 12 to 210.
These associated photodissociation and capture rates are typically
calculated with the statistical Hauser Feshbach Model (HF-Model).
The (y,a) flow is critical for the processing of heavier elements
towards lower masses in the p-process flow.
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New Resonances in 24Mg(a.y)28Si and Stellar Carbon Burning |
| 20Ne and 24Mg are important products of nucleosynthesis in stellar carbon burning. The 24Mg(a,y)28Si reaction is of significant importance for the possible subsequent depletion of 24Mg. The cross section in the stellar Gamow window for carbon burning between 1.0 MeV and 1.6 MeV is characterized by a number of resonances which are not well known.
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Direct Capture Strength in the 16O(a,y)20Ne Reaction |
| The 16O(a,y)20Ne reaction is of significant importance for stellar Helium burning. The reaction rate is low at temperatures of stellar helium burning and is therefoe identified as the "end-point" of the main reaction chain 4H(2a,y)12C(a,y)16O(a,y)20Ne which is induced by the triple alpha process.
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The PIXE-PAN Outreach Program @ ISNAP |
| A successful new program in the tradition of the JINA PAN program at MSU has been introduced at Notre Dame. The PIXE-PAN program at Notre Dame uses the existing low energy accelerator facility to introduce high school teachers and students to a two week program in material analysis techniques with accelerators.
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Reaction flow and flow hindrance in the p-process |
| The p-nuclei are stable but very rare neutron deficient isotopes of the elements above Z=42. In our present interpretation they are produced by photodisintegration processes of heavy elements in high photon-flux environments. Such conditions are expected in the type II supernova shock front heating and compressing the outer layers of the star.
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The Origin of Fluorine |
| The origin of fluorine has been unknown and speculations ran from AGB star inter-shell burning during late stellar evolution to neutrino induced production in supernova type-II explosions. Recent spectroscopic observations of post AGB stars showed strong indications of fluorine abundance in the stellar spectrum.
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The Nuclear Trigger of Type I X-ray Bursts |
| Twenty years ago it was
predicted that the reaction rate is dominated by a single resonance
with 4.03 MeV excitation energy in 19Ne. Numerous research groups
have tried to measure the resonance and its strength and determine
the trigger temperature for X-ray bursts. We have performed the
first successful measurement of the á-decay of the 4.03 MeV state
using the Notre Dame TwinSol system.
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17th Century Indian-Colonial Trade in Indiana |
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In collaboration with the Department
of Anthropology a program was initiated at the Notre Dame accelerator
facilities to analyze the composition of copper samples of Western
Indiana native heritage. The goal is to determine the providence
of the material and provide information of 17th -18th
century cultural connections and trading patterns between Western
Indiana and the British and French Colonies.
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The Rhinoceros Gastarget at Notre Dame |
| Recirculating windowless
gas-target systems are important instruments for low energy measurements
of relevance for nuclear astrophysics. The gas provides pure target
material conditions, and the beam energy loss is minimized so that
the measurements can be pursued towards very low energies. The Rhinoceros
gas-target from the University of Stuttgart has been installed at
the Notre Dame Nuclear Science laboratory for measuring the low
energy cross sections of alpha capture reactions in stellar helium
burning.
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