A modulated crossed-beam apparatus for the investigation of Penning ionization at thermal energies has been designed and constructed. Details are given for the production of a beam of helium metastable atoms by electron impact excitation. The production of well-collimated neutral beams of stable species using multi-channel capillary arrays is analyzed, and preliminary measurements on the performance of one such array are presented. Production of atomic hydrogen by thermal dissociation of is H2 discussed. A detection system is described which collects product ions and separates those due to ionization of beam particles from those due to ionization of residual gas. Preliminary analysis of the appropriate operating conditions for the pulse counting system is presented. To determine the types and abundances of ions produced in He*-neutral collisions, a magnetic sector mass spectrometer has been designed. Extraction of the product ions from the interaction region and subsequent acceleration and steering of these ions through the spectrometer are analyzed.