Data are presented for a 1-min dip in electron intensity that was observed coherently by four different University of Iowa detectors at 1546∶51 earth received time on day 244 of 1979 as Pioneer 11 crossed the orbit of Mimas inbound during its encounter with the Saturn system. By a detailed analysis we show that (1) this absorption microsignature in electron intensity is plausibly attributable to the particle sweeping effect of Mimas; (2) the radial width of the signature is caused primarily by energy dispersion in the longitudinal drift rate of electrons and not by radial diffusion; (3) the spectrum of trapped electrons at Mimas is nearly monoenergetic, centered at kinetic energy E = 1.59 MeV with a spread δE ∼ 0.1 MeV; (4) this narrow spectrum, which is unique in magnetospheric physics, is caused by the ‘band-pass filtering’ action of the successive inner satellites, most importantly Enceladus, on an inward diffusing population of electrons; and (5) the radial diffusion coefficient D of electrons E = 1.0 MeV is 1.0 × 10⁻¹⁰ R_s ² s⁻¹ at L = 4 and probably in the range 3.7 × 10⁻¹¹ to 8.3 × 10⁻¹² R_s ² s⁻¹ at L = 3.