THE FATE OF HELIUM UNDER THE CONDITIONS ON A NEUTRON-STAR SURFACE

We have studied the helium plasma in the hypernetted-chain approximati on considering both short-ranged internuclear and long-ranged Coulomb interactions. The optimal two-particle wave function has been determin ed in HNC/0 and HNC/4 approximations. The two-particle distribution fu nctions, which have been calculated in various orders of HNC/n approxi mations (n = 0, 4, 5), are used to determine the pycnonuclear triple-a lpha-fusion rate in the density regime 10(8) less-than-or-equal-to rho less-than-or-equal-to 10(10) g/cm3. The effect of this rate on the cr ust evolution of an accreting old neutron star is discussed. Our calcu lation supports the idea that the helium liquid undergoes a phase tran sition to stable Be-8 matter at densities rho almost-equal-to 3 x 10(9 ) g/cm3 as the plasma induced screening potential then becomes strong enough to bind the Be-8 ground state.