  To determine the state of spin polarization of the 3D electron gas at very
low densities and zero temperature, we calculate the energy versus spin
polarization using Diffusion Quantum Monte Carlo methods with backflow
wavefunctions and twist averaged boundary conditions. We find a second order
phase transition to a partially polarized phase at r_s = 50 \pm 2. The magnetic
transition temperature is estimated using an effective mean field method, the
Stoner model.
