  We show that the expansion of ejecta in Tycho's supernova remnant (SNR) is
consistent with a spherically symmetric shell, based on Suzaku measurements of
the Doppler broadened X-ray emission lines. All the strong K_alpha line
emission show broader widths at the center than at the rim, while the centroid
energies are constant across the remnant (except for Ca). This is the pattern
expected for Doppler broadening due to expansion of the SNR ejecta in a
spherical shell. To determine the expansion velocities of the ejecta, we
applied a model for each emission line feature having two Gaussian components
separately representing red- and blue-shifted gas, and inferred the Doppler
velocity difference between these two components directly from the fitted
centroid energy difference. Taking into account the effect of projecting a
three-dimensional shell to the plane of the detector, we derived average
spherical expansion velocities independently for the K_alpha emission of Si, S,
Ar, and Fe, and K_beta of Si. We found that the expansion velocities of Si, S,
and Ar ejecta of 4700+/-100 km/s are distinctly higher than that obtained from
Fe K_alpha emission, 4000+/-300 km/s, which is consistent with segregation of
the Fe in the inner ejecta. Combining the observed ejecta velocities with the
ejecta proper-motion measurements by Chandra, we derived a distance to the
Tycho's SNR of 4+/-1 kpc.
