Abstract
An explanation is presented for the energy shift of the electromagnetic radiation de-exciting the first 2+ state of the 10Be ternary cluster accompanying the spontaneous fission of 252Cf, a shift found experimentally to range between 6 and 26 keV for selected mass splits: we show that relativistic effects furnish both the right sign and the right order of magnitude of this shift, and this holds both for the equatorial, low-energy LCP emission mode, and for the isotropic, higher-energy LCP emission mode.