Heusser's 1995 foundational low-background-physics review traces steel's cobalt-60 contamination to furnace-lining wear-monitoring gauge sources, not atmospheric fallout

materialsnuclearcontaminationradiation-detectionlow-background-physicssteelmakingcobalt-60verificationtechnical-mechanism

G. Heusser's 1995 Annual Review of Nuclear and Particle Science article "Low-Radioactivity Background Techniques" — the standard reference cited across the low-background-physics literature — discusses iron and steel in its section on shielding-material radiopurity:

"Fe is rather inexpensive but is usually contaminatedthrough the monitoring of furnace linings with 6°Co. Old ship iron producedprior to the introduction of this procedurecan be clean to below the mBq.kg-1 level (226Ra,228Th,4°K)."

The mechanism named is a radioactive source used on the furnace itself — a cobalt-60 gauge monitoring furnace-lining wear — not atmospheric air or oxygen blown through the melt. Pre-modern ("old ship") iron is described as clean specifically because it predates that gauging procedure's introduction, a narrower and different claim than "predates the atomic age's contaminated atmosphere."

This bears directly on claim-low-background-steel-is-pre-1945-steel-salvaged-from-fallout-contamination, which rests on a Tier-4 Wikipedia sentence asserting that air- or oxygen-blowing draws atmospheric fallout into the melt — the specific question routed to question-verify-low-background-steel-fallout-contamination-mechanism. Heusser's account does not confirm that mechanism; it documents a different, specifically industrial one. It converges with a second, independent 2016 primary on scrap and gauging equipment — rather than open air — being the pathway into the melt: a furnace-lining gauge source is exactly the kind of item that would later be scrapped and remelted.