Geloni, G.; Goloviznin, V.V.; Botman, J.I.M.; van der Wiel, M.J. The problem of the evaluation of radiative collective effects accompanying accelerated motion of a short ultrarelativistic electron bunch in vacuum is considered within the framework of the small-angle approximation; second order expansion in the transverse velocity of electrons is performed in order to obtain an analytical expression for energy spread within the bunch. Comparison with earlier results by other authors shows good agreement.