[en] Time-of-flight Secondary Ion Mass Spectrometry/Direct Recoil (TOF SIMS/DR) techniques and apparatus are described which hold substantial promise for further understanding the behavior of hydrogen isotopes at surfaces. The analytic apparatus will be interfaced to a tritium-compatible exposure cell within a glovebox by means of a vacuum load-lock. Apparatus will consist of a pulsed Li/sup /plus// beam for H/D/T ratios (DR), a DC or pulsed Cs/sup /plus// beam for sputtering or TOF/SIMS (for enhancement of negative ion yields), and a dual channel 10 MHz time-digiting histogrammer for fast data rates. Prototype apparatus has already proven useful in understanding the rates at which hydrogen isotopes may be exchanged from material surfaces upon exposure to water vapor. An extremely fast and a second much slower process characterize the exchange at Si and stainless steel opxyhydroxide surface films. The fast process is limited by the rate at which water molecules strike the top monolayer of the surface. H/D exchange tunneling appears to be the bulk diffusion-limited exchange rate within the oxyhydroxide film. Diffusion constants have been derived: D/sub ex/ /minus/ 10/sup /minus/19/ and 10 /sup /minus/20/ cm²/sec for the films on 304SS and Si, respectively, at 298K and 1.3 /times/ 10/sup /minus/4/ Pa (10/sup /minus/6/ torr) [H₂O]. D/sub ex/ for 304SS is consistent with previous results on α- FeOOH and SS. Diffusion exchange appears important in understanding the behavior of tritium permeation or contamination barriers. 52 refs., 7 figs