We consider nuclear gamma decays and γ-emitting reactions that can be an efficient source of hypothetical millicharged particles (χ). In particular, we revisit the production of millicharged particles in nuclear reactor environment, pointing out that γ cascades from ^239U is an overlooked yet a powerful source of χχ pairs. This leads to an increased flux compared to previous studies. We then apply new estimates of the flux to derive novel limits on the value of millicharge, = Q_χ/e, from the electron recoil searched for in a variety of experiments placed in proximity to the reactor cores. The derived limits on are the strongest in the interval of masses 0. 7-2 \, MeV. We also derive the MCP flux from the Sun and point out potential sensitivity of the low-threshold dark matter search experiments.
Gao et al. (Wed,) studied this question.