STUDY OF DENSE HELIUM PLASMA IN THE OPTIMAL HYPERNETTED-CHAIN APPROXIMATION

We have studied the helium plasma in the hypernetted chain approximation considering both short-ranged internuclear and long-ranged Coulomb interactions. The optimal two-particle wave function has been determined in fourth order; fifth-order corrections have been considered in the calculation of the two-body and three-body correlation functions. The latter has been used to determine the pycnonuclear triple-alpha-fusion rate in the density regime 10(8) g/cm(3) less than or equal to rho less than or equal to 10(10) g/cm(3), which is of importance for the crust evolution of an accreting old neutron star. The influence of three-particle terms in the many-body wave function on the rate is estimated within an additional variational hypernetted chain calculation. Our results support the idea that the helium liquid undergoes a phase transition to stable Be-8 matter at densities rho approximate to 3 x 10(9) g/cm(3) as the plasma induced screening potential then becomes strong enough to bind the Be-8 ground state.