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

Abstract

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 melt 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.

Atomic Force Microscopy Study of Anodic Etching of Aluminum: Etching Morphology Development and Caustic Pretreatment

“…The foil denoted S in this paper had been fabricated from metal purified with a segregation process, in which the metal is separated from a liquid enriched in eutectic impurities. 13 The one referred to as T was purified using the ''threelayer'' or Gadeau electrolytic process. 13 After solidification, all subsequent rolling and annealing steps used in the processing of both foils were identical.…”

“…13 The one referred to as T was purified using the ''threelayer'' or Gadeau electrolytic process. 13 After solidification, all subsequent rolling and annealing steps used in the processing of both foils were identical. The foil compositions reported by manufacturer are given in Table I.…”

Concept of a fast neutron detector based on 10B-RPCs

“…Finally, radio-pure materials can be considered for manufacturing of the 10 B-RPC components, in particular, aluminium cathodes, as significant amounts of U and Th isotopes may be present in the aluminium ore [32]. These isotopes contribute to the background mainly due to the emission of alpha particles, which are able to reach the RPC gas gap through the converter layer [33].…”

Investigation of background in large-area neutron detectors due to alpha emission from impurities in aluminium

“…While the activity of aluminium is known in the neutron detector community [24,25], few publi-cations exist, as it is only a concern for a small subset of detectors. Concentration of U and Th in aluminium can vary greatly depending on origin; roughly, concentrations on the order of 100 ppb can be expected in standard material [19,20,21,22,23]. Surface emission rates varying from 0.05 to 0.25 h −1 cm −2 have been measured for various aluminium samples [22].…”

“…The concentration of uranium and thorium in metallic aluminium and emission rate of αparticles from the surface of the metal has been previously studied for the evaluation of the radiological hazard in metallurgy industry [19][20][21], and it is generally found to be well below the level that may cause health concerns. Furthermore, in semiconductor industry, α emissions must be well controlled as they can cause single event upsets in components such as memory [22,23].…”