ROLE OF THE SYMMETRY ENERGY IN ATOMIC MASS FORMULAS

Abstract

Cameron has interpreted the heavy uranium mass yield curve from the Mike thermonuclear explosion as indicating that conventional atomic mass formulas do not give realistic values of neutron binding energies for neutron-rich nuclei off the valley of beta stability. In this paper two mass formulas are constructed which differ in the treatment of the nuclear symmetry energy. In one, essentially of conventional form, very neutron-rich nuclei become unbound. In the other, of a modified "exponential" form, very neutron-rich nuclei remain slightly bound. The three adjustable coefficients in each formula were determined by least-squares fits to the measured masses near the valley of beta stability; the formulas fit these masses about equally well with nearly the same values of the coefficients. Additional shell and pairing corrections were determined empirically. These corrections suggest a preference for the exponential formula. Some astrophysical applications of these results are qualitatively discussed.