An alternative source for the generation of fast atom beams developed for fast atom bombardment mass spectrometry is described. The principle of operation is based on a Capillaritron ion source described elsewhere. Easy to operate with any gas and requiring low maintenance, the source should prove extremely useful for the analysis of high molecular weight compounds. Residual ions are separated from fast atoms, produced by a novel charge transfer geometry, before the beam emerges from the source. Power calorimetry was utilized as the diagnostic technique to quantify and evaluate the fast atom beam parameters. Using 8 kV Xenon beams, measurements of ion currents and power density fluxes were made with and without ion beam deflection. It was determined that the power contribution due to fast atoms in an undeflected beam can vary from 40% to 80% of the total power delivered to a target depending on the gas flow rate and ion beam energy. In one case, it is shown that 42% of the total power imparted to a probe consisted of fast Xenon atoms corresponding to a deposition at the target of 16 mW cm-'. Below a certain gas flow rate, depending on the gas, the power density was determined to be flow rate dependent. Above this value, the peak power density is constant and limited to further increases by space charge effects in the ion beam. A sample spectrum using a fast atom Capiffaritron source installed on a Hewlett-Packard 5985B quadrupole mass spectrometer is shown.