Reply #175: Radionuclides with intermediate half-lives.

[NNadir]

In the earlier series of posts on the subject of so called "nuclear waste," I deliberately covered the long lived nuclei. I did so because one feature of the general scientific illiteracy that marks the modern (or should we say re-medievalized?) United States is the belief that if something remains radioactive for a long time, it is somehow more dangerous than something that remains radioactive a short time. Actually the inverse is true, the longer the half-life of a particular nuclei, the less dangerous it is. The shorter the half-life, the more dangerous it is.

One will, irrespective of how much education one attempts to provide, always hear appalling nonsense like, "'nuclear waste' stays radioactive for millions of years..." stated as if to mean "'nuclear waste' is dangerous for millions of years." This is specious balderdash of course. It is true that the earth has always been radioactive, and always will be, unless we build so many nuclear power plants (not likely) that we actually eliminate radioactivity from the planet. In fact the only way to reduce the radioactivity of the planet overall - although it would take about a millennium to do so - is to build lots and lots of nuclear power plants. Even then, it is really not possible to eliminate radioactivity since there are some naturally occurring radionuclides, K-40 being the most problematic, that are not consumed in nuclear reactors as the radioactive elements thorium and uranium are.

Because this particular bit of illiteracy, the confusion between half-life and danger, has such staying power, I have deliberately chosen to discuss first, among the fission products, the elements that have the longest half-lives (leaving out zirconium), iodine (I-129), cesium (Cs-135) and technetium (Tc-99). However, since whatever danger is associated with particular nuclides is a function as much of their chemistry as it is of their radiological features, I have included discussions of nuclides like I-131 (half-life about 8 days) that are not particularly long lived but which, being isotopes, pretty much share the chemistry of this long lived radioisotopes with which they are associated.

In the section on cesium, I also discussed one of the more problematic nuclei in the fission product series, Cs-137. Cesium-137 (half-life 30.23 years) is what I like to think of as an "intermediate" nucleus. It has a half life that is sufficiently long lived that it is not extremely easy to simply get rid of it by letting it decay for a short period; on the other hand it is really easy to imagine - for the reasonably sensible anyway - isolating it for a few generations during which time it will decay.

In a series of posts that follow, I will discuss other elements with radioisotopes that fit this class, but which are not associated with radioisotopes having half-lives on the order of hundreds of thousands or millions of years. Some of these elements are elements like strontium, cerium, ruthenium, europium and samarium, each of which has isotopes among the fission products that have half-lives in the general range of just under 1 year to just under 100 years.

As before, I will discuss these elements in two sections, one that examines the problematic aspects of these elements, and another that examines mitigating circumstances by which such elements can be managed or rendered into uniquely useful materials.