The origin of memory effects in the Chalk River accelerator mass spectrometry sputter ion source has been studied by tracer and elastic‐recoil‐detection surface analysis techniques. For36Cl measurements, the results indicate that the memory arises from contamination of the region immediately surrounding the sample and that it can be mitigated by operating this portion of the ion source above 350 °C. This has reduced memory effects by a factor of 10 or more and has resulted in a similar improvement in background. ©1996 American Institute of Physics.