If the widow or widower of an annuitant under section 8452 (hereinafter in this subsection referred to as a “disability annuitant”) is determined under subsection (a) to be entitled to an annuity based on the service of such disability annuitant, the annuity of the widow or widower shall be equal to 50 percent of the amount determined under paragraph (2) (or one-half thereof if designated for this purpose under
section 8419 of this title), rather than of the amount referred to in subsection (a).