How is radioactive dating harmful
So over the years, your "hot" lenses are likely to get more radioactive rather than less. Lanthanum has two isotopes in its natural form, one of which is weakly radioactive.
Another source of rare earths such as lanthanum is cerite, which contains the element cerium.
Tests of one lens from one batch won't apply to another lens made from another batch of chemicals with different levels of radioactive contaminants. Roger Hicks* on Radioactive Lenses: Radioactivity in the first generation of hot lenses c.
1941-1955 is a by-product of imperfect refinement of the monazite sands used to provide the rare earths.
Another important point here is that these contamination levels vary from batch to batch, depending on the contamination in the sands used to make the impure chemicals being used.
So you have to test each lens to determine if it is radioactive, and how "hot" any given lens really is.
This was restored from a copy I made in November 2003; Bob may have added to or edited this page after that. Industar 61 lens (lanthanum glass) Lens Faults Pages Photo. Maybe some of those bargains you got on EBAY are "hot" in a different sense than you might have thought!Later lenses of the same exact design and glass formulas, but from later batches with higher serial numbers, do not exhibit any similar degree of radioactivity.Nor do they suffer from yellow discoloration over decades of time.Radioactive Elements in Glass Thorium is derived commercially from certain monazite sands (e.g., from India).Thorium is radioactive itself, emitting alpha particles.