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Stardate
20021224.1126 (Captain's log): Michael writes:
I have been talking to people for awhile now about how depleted uranium isn't the hazard that "the left" makes it out to be. I have been using an article from your web site to back this up.
But my brother, who is a supporter of the war on terrorism, found some information about depleted uranium that makes it look like a much more hazardous material than I thought. The point they make is that U-238 decays into other radioactive elements, and that the decay tree eventually produces some very radioactive substances. Here's a graphic from the web page:
Yes, it does.
But not very rapidly, and not in very great of quantities. U-238 has a halflife of 4.51 billion years, which is a figure pretty close to the actual life of the earth so far.
If I did my calculations correctly, out of a metric ton of U-238 (1000 kilograms), 153.7 micrograms will decay every year. That's not exactly what you'd call a huge peril.
You're talking about processes which are so slow that within the scope of a human lifetime they're indistinguishable from "stop".
It's like saying that a glacier is moving and thus I'm in danger of being run over by it. Yes, it's moving, but not very damned fast, and a lame snail could easily outrun it. Equally, U-238 is breaking down, but at a rate so slow as to be damned near imperceptible.
You have to compare the quantity of secondaries involved to the natural background radiation. It's not a question of whether it's actually creating radiation, it's whether the quantity involved actually represents a significant increase.
You would increase your exposure to radiation far more by moving to a new home 100 feet up a hill than by living next to a 1 ton block of U-238. Living at higher altitude reduces the amount of atmosphere between you and the sun, increasing your exposure to cosmic rays and other extraterrestrial radiation sources.
You can't ignore the issue of quantity. Leftists who are panicked by radiation have no concept of quantity; to them, all kinds of radiation and any amount of radiation is infinitely dangerous.
I don't have any idea what units that chart is using. "kBq" is not a number I've ever heard of. But did you notice that they're using a severely logarithmic horizontal scale, with entries for one year, a thousand years, a million years, and a billion years? And how it doesn't seem to be very impressive until you get out a few hundred thousand years?
Long before that point, all the uranium we've expended in those regions will have dissolved in the rain and washed out to sea.
Update: Peter writes:
The unit on the graph is the Becquerel, which is now the official SI unit for radioactive decay; it's just s-1. There's a conversion factor to curies, with 1 curie being 37 GBq. So what it does is measure how many decay events there are per second. That's not enough information to determine how dangerous the substance is, because to determine that you need to know how the substance decays (which is alpha decay in the case of U-238). Other factors also play a role, such as the total absorbed dose (measured in Gray) and a factor that determines the biological effects of the absorbed dose. This leads to the equivalent absorbed dose, which measures the actual damage to biological tissue; this is measured in Sievert. It's been a while since I actually calculated anything of the sort, so my memory is likely to be faulty here. But it would not surprise me at all if the graph measuring the decay events in Bq overstates the apparent danger, especially since U-238 decays by emitting an alpha particle rather than gamma radiation. That's not to say that alpha isn't dangerous, but you can shield it fairly easily and the intensity goes down very quickly with distance, more quickly than gamma.
But it's RADIOACTIVE so it must be VERY DANGEROUS! This reminds me of a story about the then-head of British Nuclear Fuels in the Thatcher years. He once went to speak at a conference where there were both politicians and environmentalists. He himself was a physicist. So he spoke about nuclear energy and such. And then he actually pulled a piece of radioactive nuclear waste out of his pocket and held it to a geiger counter, which went mad. The politicians and environmentalists all turned completely pale of course. The fun you can have with a slightly radioactive substance and a geiger counter set to high sensitivity...
Not to mention the fun you can have by playing games with the plotting units on the chart. Not only have they massively distorted the timescale by making it steeply logarithmic, but they've also massively increased the gain on the plot. Let's see, a curie is 37 gigaBecquerels, and this chart is being plotted at the scale of kiloBecquerels, because if they used anything like a reasonable vertical scale, the plot would lay flat on the bottom.
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