Transcript Methods used for description of astrophysics reaction rates: Carl Brune, Steve Grimes, Alexander Voinov (Ohio University) For low mass nuclei, models which.

Methods used for description of astrophysics reaction rates:
Carl Brune, Steve Grimes, Alexander Voinov (Ohio University)
For low mass nuclei, models which treat individual resonances,
such as the R-matrix method, are fitted to the available experimental
data. The cross-sections can be extrapolated down to astrophysical
energies if needed.
For higher mass nuclei (at and beyond the iron mass region),
when the level density near threshold is large, the statistical
model, using averaged optical transmission coefficients, level
densities and γ-strength functions is required, especially to model
the rapid neutron capture process.
Statistical model of nuclear reactions
Optical transmission coefficients
Level densities
Gamma strength functions
Most uncertain input parameters,
leading to factor of 2 of uncertainty
in reaction rate calculations.
The model is known. Efforts should be directed to experimental study of
input parameters.
Importance of low-energy enhancement of γ-strength function for (n,γ)
reaction rates off the stability line
A.C. Larsen et al, Acta. Phys. Pol. , B44, 563(2013).
Level density issues
• Widely used back shifted Fermi-gas level density systematics based
on neutron resonance parameters are not accurate because of
unknown spin cutoff parameter and parity distribution
• More accurate level density information can be obtained from
experimental study of particle evaporation spectra from compound
nuclear reactions. Also spin cutoff parameter can be obtained from
angular distribution of outgoing particles.
• Experimental efforts are suggested to be directed to systematic
study of alpha-, lithium- ,and heavy-ion-induced compound
reactions.
• Special efforts should be made to study of residual nuclei off of the
stability line