Po-214 is implanted into surfaces exposed to radon. The implantation rate c
ould be sufficient to explain the rate of low-energy events with anomalousl
y fast scintillation pulses that has been observed in sodium iodide crystal
s used in a search for WIMP dark matter. The rate should be closely coupled
in time to the radon concentration. (C) 2000 Elsevier Science B.V. All rig
hts reserved.