Physics – Nuclear Physics
Scientific paper
Jul 1983
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1983nupha.403..625b&link_type=abstract
Nuclear Physics A, Volume 403, Issue 3, p. 625-648.
Physics
Nuclear Physics
32
Scientific paper
The equation of state near nuclear density influences shock formation in stellar collapse Supernovae. The drop in the adiabatic index below 4/3 in this region, due to the negative nuclear pressure, disturbs the homology of the inner core and decreases its size. The initial shock energy and formation dynamics are particularly sensitive to matter in this regime.
Only matter at low entropies (S <= 1.5) in the unshocked inner core approaches nuclear densities. We derive a simple equation of state for this material and find that nuclear properties are close to those at S = 0. The entropy associated with the nuclear surface can be absorbed into an ``effective mass'' which decreases towards one with increasing density, giving an accurate accounting for the storage of entropy in the excitation of the large nuclei. Such thermal excitation drains energy with little contribution to the pressure and thus may have important effects on the launching of the shock.
Two phase transitions are considered. The first, from the heavy nucleus to the ``bubble'' phase, occurs at half nuclear matter density and is accomplished by use of simple expressions for the energy and pressure that include effects of the transition implicitly. The second, that to uniform nuclear matter, is done by requiring continuity of the pressure and entropy at the transition. The density at which this transition takes place is calculated and is found to decrease with entropy in a simple manner.
With the use of suitable approximations, the equation of state is presented in a non-iterative form easily adapted for use in full hydrodynamical calculations of the supernovae process. Comparison with more detailed equations of state is made and the simplified one is found to represent well all important features.
Supported in part by USDOE under Contract No. W-7405-Eng-48.
Bethe Hans A.
Brown Gerald E.
Cooperstein Jerry
Wilson Richard J.
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