A strong gravitational field resulted in the sedimentation of isotope atoms in monatomic liquid. The concentration ratio (82)Se/(76)Se increased by greater than 3.5% in specimen ultracentrifuged at (0.7-0.9) x 10(6) G and at 300 degrees C. The recovered sample had a feather-shaped crystalline morphology. The concentration gradient was nearly twice that of the steady state analytical result (ideal gas system), indicating a nonideal system diffusion. The present result is evidence of sedimentation of substitutional atoms in condensed matter via self-diffusion and suggestes its possible application to isotope separation, crystalline control, and matter dynamics in massive star. (c) 2007 American Institute of Physics.