[en] A small Penning-type ion source with an ion-current-neutral conversion sensitivity of 2 x 10^-2 A torr^-1 has been constructed. Ion extraction is by way of a channel in one magnet pole face where a retarding-potential plot has shown that 95% of the ions have an energy less than 100 eV. The source is utilized with a high-energy ion stop and a quadrupole mass filter with an out-of-line-of-sight ion collector. (orig.)