Alpha Rays Emitting Impurities in Ultra Pure Aluminum Evolution Through the Successive Refining Steps

M. Leroy
1995 Journal de Physique IV : Proceedings  
Alpha rays are a major source of software errors in integrated circuits, especially in DRAM memories. A major aim of refining techniques used for the production of Ultra-pure aluminium alloys is therefore to eliminate radioactive impurities. This elimination was studied all along the refining steps from the ore (bauxite) to Ultra-pure aluminium. A major observation is that Radium isotopes accumulate in the caustic soda liquor, used for production of alumina from bauxite and in the cryolithic
more » ... t used for production of primary aluminium from alumina. Accumulated isotope Radium 228, which has a rather short half-life, disintegrates by k m i s s i o n to Thorium 228, which then transfers immediately to cathodic aluminium metal. This induces a strong disequilibrium in the decay chain of Thorium 232, and, as a result, more than 80 % of the total alpha-emission of Ultra-pure aluminium comes from alpha-decay of Thorium 228 and its daughters, which are in equilibrium with Thorium 232. As a consequence, the content of Aluminium in U 238 and Th 232 (the only isotopes measured by GDMS or ICP/MS) can just give a rough order of magnitude of Alpha-emission, the Th 232 family being by far the most deleterious as regards software errors. (?) 0.13 | 0.114 J 0.011 J
doi:10.1051/jp4:1995708 fatcat:c7g3ysfqszfa3bcrpzslqu4eiy