The explanation of why steel made since 1945 is radioactive has always seemed weak to me. Yes, there is a barely detectable cobalt-60 contaminant in air from above-ground weapons trests, but there are many more isotopes as well. Is there enough Co-60 to be detected in steel?
Recently I learned a more plausible explanation, from a physicist who worked at Brookhaven National Lab in the 50s. The Atomic energy Commission, eager to make radioisotopes useful in all industrial ventures, suggested making fire-bricks laced with Co-60. When used to line steel-making furnaces, one could measure the degree of wear in the liner by simply counting the gamma rays out of the bricks. When the bricks got very thin, the radiation would fall off appropriately, and the furnace was shut down for re-bricking. The steel industry was delighted, and incorporated the suggestion. It was bad when a furnace would burn-through without warning.
This was great for the steel industry, but it deposited a steady stream of Co-60 into all new steel, as the bricks ablated into the molten metal. In my opinion, this makes a better explanation of the radioactive metal. Read all about it and other charming nuclear myths in my book, Atomic Awakening: A New Look at the History and Future of Nuclear Engineering.
The information is very interesting, and thanks for sharing it.
However, I hope you deal with it much more thoroughly in your book. As it stands, you’ve raised more questions than answers.
If the use of cobalt-60 bricks was universal in the industry, then there should be volumes of information about the use in all standard references and journals about steelmaking. I assume threfore you’d have sources in depth far more than a comment from someone not in the industry.
The next question, however, is whether it really was universal. Did every steelmaker use this technique? In the U.S. and in every other country? If not, then why would the testers have to do anything more than place a phone call to one of the firms not using cobalt-60 bricks?
I don’t doubt that the technique was used. The Health Physics Society talks about it. But not as something universal.
And it may be that the cheapness of using scrap outweighed any advantage from finding processers who didn’t use cobalt-60 bricks. I just don’t feel that we have enough information from your post to understand the industry at the time.
The contamination of Co-60 in steel is well under regulatory concern. It is of no bother to anyone, unless you are counting low-level radiation. It has received little official notice.
It is not necessary for cobalt-laced firebricks to be in everyone’s steel mill for it to quickly contaminate the entire world. Scrap steel from the US, with its cobalt-60, has been used for decades by steel mills all over the place, mostly in Asia. Cargo ships need something to take back with them from the US, and scrap steel is inexpensive and easy to load. We are usually glad to be rid of it. Steel is recylcled, over and over, and eventualy the Cobalt-60 finds its way into everything ferrous.
A quick gamma-ray spectrum of a steel sample tells why we think it’s specifically cobalt and not fission products. Two gamma peaks form cobalt-60 stand up, and not much of anything else does.
So as not to clutter up the forum with another thread, I’ll just put my comment here. This:
Seems overly snarky and not necessary. I know that’s your style but not all of us are science majors. And be honest, you had to look most that stuff up didn’t you?
I find it very hard to believe that Cobalt-60 contamination in steel in 2010 could be traced back to airborne radiation from tests that occurred between 47 and 65 years ago. Cobalt-60 has a half-life of 5.27 years. The material from those tests has gone through 8 to 12 half-lives. Also after 50 years in the environment there is very little bomb testing fallout just blowing in the wind.
Also that answer was far more snarky that the question deserved.
The column of December 10, 2010, “Is steel from scuttled German warships valuable because it isn’t contaminated with radioactivity?” was pretty much spot on, as usual. A couple of additional points seem called for, however.
As nuclear power plants are decommissioned, low-level radioactivity is finding its way into the metals industry via scrap. In addition, dozens of cases have been reported of high-level sources intended for radiotherapy or industrial radiography finding their way into the scrap stream, sometimes illicitly. (1)
A couple of other commentators have mentioned that in the golden days of nuclear applications, cobalt-60 was used to monitor the thickness of firebrick in blast furnaces. A blob of Co-60 was embedded in the brick and its gamma rays were measured from outside the furnace. When the counting rate went way down, it was a signal that the brick was burning through and needed to be replaced. Of course, the Co-60 dissolved in the melt, but a few millicuries in hundreds of tons of iron and slag is no health hazard. Because the half-life is 5.3 years and steel is endlessly recycled, all ordinary iron nowadays may be contaminated at some level. As Cecil pointed out, only if you’re doing low-level radioactivity measurements do you need to know this. (2)
In lead, the problem is radioactive lead-210, a decay product of uranium and radium. Some lead veins are less radiogenic than others, but even the cleverest chemistry can’t remove this isotope from common lead. The only way to get it out is to let it decay through many times its 22-year half-life. Roman ship anchors are the classiest source, but medieval church roofs and colonial Boston sewer pipes have their admirers.