An ion pump with a housing enclosing an interior, a gas inlet having a through-hole extending into the interior of the ion pump, at least one cathode, at least one anode positioned in proximity to the at least one cathode, a magnet disposed on an opposite side of the at least one cathode from the anode, and a blocking shield disposed between the gas inlet and the at least one cathode. The blocking shield is electrically connected to the at least one anode. An associated method installs the blocking shield by inserting components of the blocking shield assembly through the gas inlet, and assembling (inside the interior of the ion pump) the inserted components to form the blocking shield.