Clean galena, contaminated lead, and soft errors in memory chips

Lead (Pb) disks were exposed to a radon (Rn)-rich atmosphere and surface al pha particle emissions were detected over time. Cumulative Po-210 alpha emi ssion increased nearly linearly with time. Conversely, cumulative emission for each of Po-218 and Po-214 was constant after one and two hours, respect ively. Processing of radiation-free Pb ore (galena) in inert atmospheres wa s compared with processing in ambient air. Galena processed within a flux h eated in a graphite crucible while exposed to an inert atmosphere, resulted in lead contaminated with 210Po (Trial 1). A glove box was next used to pr epare a baseline radiation-free flux sample in an alumina crucible that was heated in an oven with an inert atmosphere (Trials 2 and 3). Ambient air w as thereafter introduced, in place of the inert atmosphere, to the radiatio n-free flux mixture during processing (Trial 4). Ambient air introduced Rn and its progeny (RAD) into the flux during processing so that the processed Pb contained Po isotopes. A typical coke used in lead smelting also emitte d numerous alpha particles. We postulate that alpha particles from tin/lead solder bumps, a cause of computer chip memory soft errors, may originate f i om Rn and RAD in the ambient air and/or coke used as a reducing agent in the standard galena smelting procedure.