  We suggest a long-lived spin polarization structure, a radial spin helix, and
study its relaxation dynamics. For this purpose, starting with a simple and
physically clear consideration of spin transport, we derive a system of
equations for spin polarization density and find its general solution in the
axially symmetric case. It is demonstrated that the radial spin helix of a
certain period relaxes slower than homogeneous spin polarization and plain spin
helix. Importantly, the spin polarization at the center of the radial spin
helix stays almost unchanged at short times. At longer times, when the initial
non-exponential relaxation region ends, the relaxation of the radial spin helix
occurs with the same time constant as that describing the relaxation of the
plain spin helix.
