What if I told you that a material existed with the following properties?
- It is highly radioactive. Because it is a very high energy alpha emitter, it is very radiotoxic. It also produces a long decay chain of daughters that emit high energy gamma and beta particles.
- It has a half-life of over one thousand years, making it difficult to dispose of and requiring long term storage considerations. Despite the relatively long half-life, it is still short enough to make it highly radiotoxic, especially because of the nature of the radiation it emits directly and through its daughters.
- It emits enough gamma radiation that a pure sample of the material can kill tissue on contact, after only exposure of a few minutes.
- The gamma radiation emitted by the material and its daughters is sufficient that if you sat next to a few dozen grams of the material, you could easily end up with acute radiation sickness in a matter of hours. In less than a day it could kill you.
- A pure sample emits enough radiation to create significant amounts of heat. The total decay heat is more than 100 watts per gram.
- It is chemically reactive, it forms compounds which readily dissolve in fresh and salt water. It may be mobile in the environment, but it also may cling to materials, making decontamination of areas difficult.
- It has a high biological uptake in most of its chemical forms.
- It may be persistent in the body and has a tendency to be incorporated into bones, replacing calcium. In such cases, it will not clear the body and has been associated with leukemia and bone cancer.
Such a substance does, in fact, exist: radium-226. Gram per gram it’s more toxic than plutonium-239, the isotope most common in spent fuel. It’s a highly energetic particle emitter that does not decay to a stable isotope but rather to a long chain of other radioactive substances. First it decays to radon-222, then to polonium-218, astatine-218, radon-218, lead-214, bismuth-214, polonium-214, thallium-210, lead-210, polonium-210 and finally lead-206, which is stable. For this reason, a chemically pure sample will actually increase in radioactivity until it reached equilibrium with its daughter products. Despite the relatively long half-life, it produces a great deal of radiation because for every decay of radium-226, there are decays of all the other daughters all the way down the line. Some of these emit high energy gamma rays. Radon poses some additional challenges. Because it is a gas, it may not remain in place and can result in the area around a radium-226 sample accumulating potentially dangerous concentrations of radon. The radon gas can also disperse, contaminating the area with further decay products.
Despite these dangers, radium-226 was once far more valuable than gold. For the first half of the 20th century, radium and its decay products were the most widely used radioisotope source for any purpose that required radioactive materials. It was used for cancer treatment, in the form of radium needles, external sources and devices that collected radon for use in irradiating tissue. Radium was commonly used in any circumstance where calibration sources were required, with many earth geiger counters coming with a radium-based test source. It was used in ion and moisture gauges, cold cathode vacuum tubes and combined with beryllium to produce small neutron sources. Radium was well known for its use in radiolumonescent paints. The paint was commonly used for clock and watch faces, allowing them to glow brightly without first having to be exposed to light. Larger concentrations were used for aircraft instrument dials, illuminated markers and cords. It was realized that the heat from radium could be used as a means of powering boilers or other thermal engines, but was far too expensive to ever be used in this capacity. It also was experimented with in early “nuclear battery” designs.
Radium-226 exists in small concentrations in uranium ore. To recover a single gram of the material, several tons of uranium ore must be processed. Still, because the material had so many uses and was so valuable, large operations existed all over the world to produce it. In the 1920′s, a gram of radium could cost as much as $120,000, (about 1.3 million USD in modern terms) though the price later fell to $75,000 due to more efficient production techniques. Radium needles could contain up to .1 grams of radium, making them worth more than ten thousand dollars. Because of this, radium was also used as an investment commodity. Radium needles and other radium sources were kept in bank vaults in the same way gold, silver and platinum might be kept.
Of course, radium is also pretty dangerous for the reasons mentioned above. Its chemical properties make it prone to contaminating areas and easily absorbed into the body, where it is distributed into bones and teeth, making it an especially persistent and damaging substance. It produces a great deal of alpha, beta and gamma radiation, which is not desirable for most situations. Its half life is inconveniently long for applications where disposal after a period of time is expected and the production of radon can be a danger and complicate its use. For radiolumonescent items, gamma radiation is not desirable and the energy of the alpha particles emitted by radium has a tendency to degrade the phosphorescent compounds in the paint over time. Radium was blamed for a number of deaths and illnesses, most notably in the “radium girls,” who worked in clock factories, painting the hands and numbers of clocks with radium paint. Some were encouraged to lick their brushes to sharpen them, resulting in ingestion of large quantities of radium.
Because of this, radium-226 fell from favor as a radiation source for most applications as soon as synthetic, reactor-generated isotopes became available. By the 1960′s, safer, more well suited isotopes had taken over. Radiolumonescent items used soft beta emitting isotopes like prometium-147 and tritium. External cancer treatment or the irradiation of products used cesium-137 or cobalt-60. Cesium-137 became the most common isotope for testing and calibration of survey equipment, and for applications that required alpha radiation, synthetically produced polonium-210 or americium-241 became the isotopes of choice. Such isotopes produce forms of radiation more suited to their end use, rather than a hodgepodge of alpha, beta and gamma emissions of multiple energy levels. They tend to be shorter lived, allowing for small quantities to generate sufficient radiation and reducing the problems of long term disposal. Many are easily made into forms that are chemically inert, physically stable and not prone to dissolving in water or accumulating in organisms.
Today, radium-226 is no longer intentionally produced for its own use. It may occasionally be used in calibration source for spectrometry and a few other scientific applications, but only in relatively small quantities. Radium clocks and other luminescent items are still common in antique shops and are not generally considered to be a major hazard. However, some aircraft instruments and military items are radioactive enough to make them a concern for regulators (whether this is actually necessary is another matter.) Radium needles and therapeutic sources are unquestionably very dangerous. They still turn up from time to time, though most have been removed from the inventories of hospitals and other locations. Today they are treated as high level waste and must be carefully removed, isolated and disposed of at licensed facilities. The half-life and properties of radium can make it especially challenging.
Radium also contaminates numerous areas around the world due to past activities such as refining of radium, paint production, clock manufacturing and maintenance of aircraft with radium-painted instruments. Radium tends to be very difficult to clean up. It can contaminate local ground water, it may cling to soil or may become mobile in the local biosphere. Often, the only solution is to remove huge quantities of soil and transport it to an area where it can be immobilized and monitored.
By almost any standard, radium-226 is more toxic, more dangerous and more problematic than almost any other type of radioactive material. Like plutonium, it will persist for thousands of years, but it’s far more toxic and more reactive. It’s more difficult to immobilize than most substances in spent fuel and is usually in a form that is less chemically stable and contained. Gram per gram, it produces more heat than spent fuel or most transuric elements. Highly concentrated radium-226 makes spent fuel appear very tame. Even compared to more concentrated waste, such as the fission products generated by reprocessing, radium-226 is still more difficult to dispose of safely.
By the time production of radium-226 began to come to an end, in the mid 1950′s, about 2.5 kilograms had been produced worldwide. Yet that’s only a tiny proportion of what exists on earth. Since radium-226 is natural, a decay product of uranium, huge quantities already exist on earth and always have. There are at least fourty trillion tonnes of uranium in earth’s crust and billions of tons more dissolved in seawater. Many times more uranium exists in the earth’s interior. For every one tonnes of raw uranium, there exists about .143 grams of radium-226. (note: value converted from reference in short tons). That means that there is already 5.72 million tonnes of radium-226 in earth’s crust.
By comparison, the total world inventory of spent fuel is only 188,000 metric tonnes, although additional spent fuel is reprocessed, largely being reused, but with some remaining fission products and contaminated material for disposal. If the slightly radioactive uranium were removed from spent fuel, more than 90% of the mass would be gone, and the material, though more radioactive, would still be less toxic, less reactive and generally less hazardous than radium-226.
The bottom line is that there’s more radium-226 in the environment we live in than spent fuel and gram per gram it’s far more dangerous.
So why is this not a problem? Mostly because it’s not heavily concentrated in any one place. If it were, that small area could be dangerous, but because most of the uranium on earth is distributed across the crust in relatively low concentrations, so is the radium. This one natural isotope has always been there and yet the sky is not falling. We all even have a fraction of a pictogram of it in our bodies. And while I’m not suggesting spent fuel should just be dispersed across the globe or dissolved away in the world’s oceans, if it were, it would result in significantly less radioactivity than the radium-226 that is already there, which is only one of the many naturally occurring radioactive substances.
On a global scale, the hundreds of tonnes of spent fuel is just not a big deal. We obsess about preventing it from entering the environment, but forget that the environment already has a material in it that is far more dangerous and present in much larger quantities. If we can live in a world with that much radium-226, plutonium-239 and cesium-135 are really no big deal.
This entry was posted on Sunday, February 19th, 2012 at 6:30 pm and is filed under Bad Science, Enviornment, Good Science, History, Nuclear. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.
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