Radiation and radioactivity were discovered more than a century ago and it didn’t take long to realize that they could burn the skin. From there it wasn’t too great a leap to realize that perhaps they could also be used to deliberately burn tissues – tumors – and the field of radiation oncology was born. A century ago, however, physicists had not yet created the artificial radionuclides that are the backbone of today’s nuclear medicine and radiation oncology – Cs-137, Co-60, Ir-192, and so on – they had only the natural radioactivities, primarily radium (Ra-226) and the nuclides into which it decayed. Radium itself was hideously expensive, but it decayed into radon (Rn-222), which decayed further into isotopes of lead, polonium, and bismuth.
Radon being a gas, it could easily be extracted from the radium ore and would then be loaded into tiny gold capsules that were sealed – these “seeds” were then inserted into tumors in order to treat cancer. And to make sure that they had enough (in those very early days of medical imaging) the doctors tended to order more seeds than they ended up using. The extras often ended up being sold to gold buyers and were melted down and frequently sold to jewelry manufacturers…along with the radioactive lead, polonium, and bismuth it contained.
Fast-forward nearly a half-century to the 1960s when doctors began reporting patients with odd skin conditions that were eventually identified as radiation dermatitis – not necessarily radiation burns (those take a higher dose over a shorter period of time), but skin damage, pigmentation changes, and damage to the underlying cells; one patient even died of skin cancer that was likely caused by the radiation. While it took some time, physicians and public health officials came to realize that the skin damage was due to radioactivity in the jewelry they were wearing; gamma spectroscopy showed the radionuclides to be radon decay products and more detective work revealed the origin to be the decades-old gold capsules.
Once the source of the contamination was known public health officials let the public know what was going on and offered to survey any gold jewelry brought to them – especially antique gold. Of about 160,000 pieces of jewelry examined, 155 were found to contain radioactivity; 133 of these were turned over to the government for disposal and the other 22 were kept by their owners. Of the pieces collected, the majority dated back to the 1930s and 1940s, although one ring was engraved with the year 1910.
Two factors seem to have made the difference between those who developed radiation dermatitis and those who did not, as well as the varying degrees of severity among those afflicted: the amount of radioactivity that was present in the gold and the amount of time that it was worn; the type of jewelry played a role as well, albeit not as important as the other factors. A wedding ring, for example, would likely be worn continually for years or decades and, as a ring, would be in closer contact with the skin compared to, say, a brooch or a pendant – an amount of radioactivity in a wedding ring, then, would be expected to produce more serious skin damage than in a brooch or a pair of earrings.
There haven’t been any cases of radiation injury from radioactive jewelry in several decades; this doesn’t mean that every bit of contaminated gold has been accounted for; most likely any contaminated jewelry that remains is only lightly contaminated or is being held as a family heirloom rather than something that is worn frequently. In any event, whatever is left of this contaminated gold appears to pose little risk.
A decade ago I became aware of another area in which radiation and jewelry cross paths – it turns out that radiation can cause some gemstones to change color, and some of these changes are for the better. Topaz, for example, can change from a fairly ordinary straw color to a much more attractive blue; diamonds can turn green and bluish-green (they can turn yellow or brown, but that was found to be due to thermal heating of the gems placed in the beam of a particle accelerator), and other gemstones can turn still more colors. The way it works is that the color of a gemstone (or anything else for that matter) is a function of the manner in which light interacts with it – in gemstones it has to do with what are called “color centers” and these color centers can be affected by exposure to ionizing radiation. Not only that, but different types of radiation and different irradiation periods can cause different kinds of color changes!
One example of this is with blue topaz, which is typically exposed to either neutrons or to high-energy electrons. Neutrons weigh about 2000 times as much as electrons and they cause more ionization within the crystal; at the same time, they are also large enough to jostle atoms around within the crystal structure or even to be captured by an atom, causing it to become radioactive and to decay to form an atom of a different element. On the other hand, the much lighter electrons don’t do nearly as much when they interact with the topaz crystal – they can cause ionization and minor changes, but that’s about it. So topaz that’s irradiated with neutrons ends up being a much darker blue than electron-irradiated topaz. Or, to put it another way, topaz that’s placed in a nuclear reactor core (which is a great source of neutrons) will be a deeper blue than the topaz that’s placed in the beam of an electron accelerator.
Here’s the thing, though – slamming neutrons into atoms can make them become radioactive and, if the electron energy is high enough, so can electrons. So irradiated gems makes them more attractive, but it can also make them radioactive – the question is whether or not they become radioactive enough to pose a threat to the wearer.
This was enough of a concern that a number of studies were done to try to evaluate the threat (if any) these gems posed, including a few studies performed or funded by the Nuclear Regulatory Commission, as well as by some gemological organizations. And they all found the same thing – that the gems are radioactive, but not to the point of causing problems. And some of the reasons for this are different for different types of irradiation.
One reason is that the elements of which most gemstones are comprised don’t lend themselves well to becoming activated, so not much radioactivity is produced to begin with; on top of that, most activation products decay away fairly quickly, so it’s not too big a deal to store the gems until most of the activity that is induced is gone, and the traces of longer-lived radionuclides that remain are present in quantities too low to cause a problem. And there’s an additional factor that comes into play with electron-irradiated gems – unless the electrons have a lot of energy they won’t strike any atoms hard enough to eject them from the nucleus. Or, put another way, electrons can’t induce radioactivity unless they’re very high-energy – higher than what most accelerators are capable of producing.
OK – so I mentioned that there might be traces of radioactivity left in some of the gems, but that it’s not dangerous…and you might wonder how I can say that so confidently. Well, it turns out that there are traces of radioactivity in a lot of things – including all of the food that we eat and in the water that we drink. In most cases, our food and water contains more of this natural radioactivity than do irradiated gems. I’ve made measurements on both irradiated gemstones and bananas and salt substitute (both of which contain naturally radioactive potassium-40), and it turns out that a bunch of bananas gives off more radiation than even a pound of irradiated blue topaz that’s been cut, mounted, and ready to sell.
In addition to materials that have been made radioactive by people there are also some gems with natural radioactivity – primarily uranium and thorium and their decay products. But these, too, pose no risk to the wearers. If you’re interested in reading more about this topic, here are some links that might be useful. Some of these reports are a bit technical, but they all contain a great deal of useful information:
The Radioactive Decay Patterns of Blue Topaz Treated by Neutron Irradiation
Health Risk Assessment of Irradiated Blue Topaz (NUREG 5883) – Nuclear Regulatory Commission, 1992.
A History of Diamond Treatments – Overton and Shigley, 2008