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

Lead (Pb) disks were exposed to a radon (Rn)-rich atmosphere and surface alpha particle emissions were detected over time. Cumulative ²¹⁰Po alpha emission increased nearly linearly with time. Conversely, cumulative emission for each of ²¹⁸Po and ²¹⁴Po was constant after one and two hours, respectively. Processing of radiation-free Pb ore (galena) in inert atmospheres was compared with processing in ambient air. Galena processed within a flux heated 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 prepare 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 was thereafter introduced, in place of the inert atmosphere, to the radiation-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 emitted numerous alpha particles. We postulate that alpha particles from tin/lead solder bumps, a cause of computer chip memory soft errors, may originate from Rn and RAD in the ambient air and/or coke used as a reducing agent in the standard galena smelting procedure. Author’s Note: No-alpha lead (NAL) as used in this article is a misnomer. What is meant is lead in which the alpha particle (α) emission is so low that it cam not be detected with current instrumentation and t memory chips are not affected by α emission from lead solder bumps.