The ground state energy of a six-neutron drop is computed with variational and Green’s function Monte Carlo methods using the Argonne $v_{18}$ two-nucleon and the Urbana three-nucleon potentials. Combined with earlier results from investigations of the drops ${}^{8}n$ and ${}^{7}n,$ this energy gives a $1p$-shell pairing energy of $(1.8\mathrm{}\pm 0.4)\mathrm{MeV}.$ The generalized Skyrme effective interaction discussed in the earlier work is applied to these nuclei by calculating, for the open-shell drops ${}^{7}n$ and ${}^{6}n,$ the matrix elements of the Skyrme $t$ matrix directly for the states involved. The pairing energy obtained is 1.50 MeV, in reasonable agreement with the accurate calculations.

• Received 22 May 1997

DOI:https://doi.org/10.1103/PhysRevC.56.2549