Hi all; On the subject of depleted uranium.
While looking for past commentary on inspections by Steven den Beste, I noticed that he has recently made silly statements on the subject of depleted uranium. While I agree with him that DU is not enough of a hazard to have killed significant numbers of Iraqis, he's dead wrong about several comments on the subject.
The reason that people are easily confused on this subject is that the stuff has such a long half-life, 4.5 billion years, and it's only decay is through an alpha particle which is easily shielded.
The first thing to note is that while U238 decays through an alpha particle, the decay chain that transforms the original U238 to the stable Pb206 includes beta particles as well. In total, a single U238 atom eventually produces 8 alpha particles and 6 beta particles on its long road to lead (as well as some neutrinos that we'll ignore because they are not dangerous). (By the way, the decay chain from U238 to Lead is one of the sources of scientific evidence for the age of the earth.)
health.state.ny.us
The 13 decay products after the first alpha particle have various half lives from miliseconds to 233 thousand years. The immediate result of alpha decay in U238 is Thorium 234 which decays through beta decay with a half life of 24 days. Since 24 days is much shorter than the typical age since the chemical purification of the U238 itself (i.e. the age of the DU munition itself), the decay rates of Th234 will approximately equal the decay rates of U238. The same applies to the result of the next decay, Protactinium Pa234, with a half life of 1.1 minutes, but the resulting U234 has a half life of 233 thousand years.
So from the point of view of radiation exposure on a battle field, we only need to look at the first three decays and can safely ignore the remaining eleven decay products. The environmentalists will argue that we should take into account the radioactivity that results from that 233,000 year delay, which will more than quadruple the total number of decays, but U238 with two beta decays and an alpha decay is radioactive enough that we don't need to go that far. Just remember that it starts out this radioactive, and as time goes on, it eventually gets almost 5x worse. That's why those long term charts of U238 show rising levels of radioactivity, as indicated in the useful plot in the following link. The following calculations use the level of radioactivity as indicated in the region between "1" and "1000" years:
denbeste.nu
For computing radioactivity levels, it is useful to know that the conversion between decay rate and half life is Thalf = ln(2) / Rate.
cbu.edu
For comparing the activity results with standard measures of radioactivity, it is useful to know that a becquerel is equal to "one disintegration or nuclear transformation per second." (A Curie is 3.7x10^10 disintegrations per second.)
whatis.techtarget.com
The measurement of radioactivity I'll use is becquerel/kilogram or becquerel/kg or Bq/Kg. To compute this, we need to know the number of U238 atoms per kg. This is computed using Avogadro's Number, 6.022 x 10^23, and the atomic mass of U238, which is, well, pretty close to 238.
gemini.tntech.edu
N = 1000g/238 * 6.022 x 10^23 = 2.53 x10^24 atoms.
From the relation between half-life and rate, and the fact that there are 31.6 million seconds in a year, the rate at which a single U238 atom produces disintegrations (subject to the above assumptions of age between 24 days and 250K years) is:
Rate = (ln(2) / (4.5 x10^9 years)) * (1 year / 31.6 x 10^6 seconds)
= 4.88 x 10^ -18 /second.
Therefore the becquerel/kg for U238 is:
4.88 x 10^-18/sec * 2.53 x 10^24 Atoms/kg = 1.2346 x 10^7 becquerel/kg.
This is compatible with the figure for specific activity of U238 of "1.245e+04 Bq/g" given in this link:
peacelink.it
From the above, it should be very clear that the radioactivity of U238, as usually quoted, only includes the first alpha delay, it ignores the immediately following (in a matter of weeks) two beta particles, as well as all the other decay products that happen over the millenia. Assuming that the decay products don't contribute to the radioactivity of DU is a basic error that is fairly common among conservative bloggers. This is "misleading" at best. For example, in Steven den Beste's case:
But ignoring that, it's also the case that U-238 is almost non-radioactive. In fact, a Geiger counter will react more strongly to a human than it will to an equal mass of depleted uranium, because the trace amounts of carbon 14 and potassium 40 (both of which are beta-sources) in our bodies cause more actual radiation.
denbeste.nu
The above quote is false on its face in that it implies that DU munitions have no beta radiation when in fact they have exactly 2x as much beta as alpha disintegrations, but looking at the other side of the above claim, just how radioactive are our bodies? Carbon-14 has a half life of 5714 years, and so is very much more radioactive than U238, but it is a very tiny percentage of all carbon, only one atom out of every 10^12.
irb.hr
Using the above information, we can compute the bq/kg for the Carbon in our bodies (which is only a portion of our mass so this is an exaggeration of our degree of radioactivity):
N = 1000/12 * 6.022 x 10^23 = 5.02 x10^25 atoms.
Rate = (ln(2) / 5714 years) * (1 year / 31.6 x 10^6 seconds) * (1 / 10^12)
= 3.84 x 10^-24 / second.
Therefore the bq/kg for carbon is:
3.84 x 10^-24/sec * 5.02 x 10^25 Atoms/kg = 193 bq/kg.
The result is that U238 is 64000 times more radioactive than the Carbon in our bodies. A similar calculation can be made for the K40 content. K40 has a half life of 1.26 billion years (about 4x more radioactive than U238), but only about 1 Potassium atom in 8500 is Potassium-40, and the decay chain only includes a single decay, to Ar40 or Ca40, either of which is stable. In addition, the average adult male contains about 140 g of K, which makes this whole discussion on radioactive Potassium even less important:
rerowland.com
Here's another reference, this one giving the power in uW/kg for U238 and the K40 component of Potassium.
U238 94.35
K40 0.0035
earth.rochester.edu
But is this level of radioactivity even detectable? The short answer is: Hell yes!!! U238 is about 10,000 times more radioactive than the worst soils in Poland:
clor.waw.pl
Fruits and vegetables in Yugoslavia:
oita-nhs.ac.jp
The Distribution of Naturally Occurring Soil Radionuclides and Radon Potential of Northwest Oregon
nwdata.geol.pdx.edu
Radioactivity in foods:
hps.org
US food limits for radioactivity:
Derived Intervention Level (DIL): a protection action guideline issued in draft form only by the Food and Drug Administration pertaining to contamination of human foodstuffs and based upon a committed effective dose equivalent of 5 msv, or a committed dose equivalent to individual tissues and organs of 50 msv, whichever is more limiting. Typical intervention levels expressed in becquerels / kilogram (1 bq = 1 disintegration per second = 27 picocuries) of contaminated foodstuffs are 131i: 167 bq/kg (1 year old child), 137Cs: 1360 bq/kg (adult), 239pu: 2.2 bq/kg (3 month old infant), 241am: 2.0 bq/kg (3 month old infant) the new fda guideline is especially noteworthy in extending the dil's to include a variety of radioisotopes not considered to be of much importance until after the Chernobyl accident e.g. 129I: 56 bq/kg (10 year old child).
nuclearhistory.tripod.com
So what would we do if terrorists spread U238 around a city with a "dirty bomb"? Would we be able to ignore this because the level of radiation would be less than the amount put out by the human body? (LOL!!!) Of course not. U238 puts out 12 million bq/kg, with the decay products formed in a few weeks time, the stuff puts out 36 million bq/kg. By comparison, "low level" nuclear wastes are "generally one million becquerels per kilo at the most".
stuk.fi
This document refers to uncontaminated items as having a level of contamination less than 400 bq/kg. And of course the eco types are complaining about even that much radiation:
llrc.org
Coal ash is known to be radioactive. The amount is around 2600 Bq/kg, which is about 5000 times less radioactive than U238:
uic.com.au
U238 would be classified as "intermediate level waste" by the British:
In the UK, radioactive wastes are classified into three main categories: high, intermediate and low level waste (HLW, ILW, LLW respectively), according to their levels of radioactivity and heat-generating capacity. LLW is defined as waste material that has a radioactive content above 400 becquerels 1 per kilogramme (Bq/kg), but not exceeding 4 million Bq/kg of alpha activity or 12 million Bq/kg of beta/gamma activity. The radioactive content of ILW is above the threshold for LLW, but not sufficiently great to result in significant heat output from the waste. HLW is highly radioactive and consequently generates significant heat such that this has to be taken into account in managing the waste.
energy.org.uk
Hungary's definition:
npp.hu
The US steps around the issue by defining U238 as "source material":
nuc.berkeley.edu
Also see:
ameslab.gov
In other words, U238 is 12x worse than low level nuclear wastes. If we get this dumped on a city we're going to have a clean-up problem from hell on our hands no matter what Steven den Beste and the other neoconservative commentators think. That people with college degrees could make these arguments is at most an indictment of our education system, not an indication that DU is safe.
-- Carl
P.S. Also see:
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.
denbeste.nu
While the leftists are "panicked by radiation", Steven den Beste doesn't know the first thing about the subject, nor is he even willing to do the simplest calculations on it. Yet he blogs on, despite a nearly complete state of ignorance. The basic problem is that radiation isn't so simple that it can be fully explained in a sound-bite. I doubt that he'll ever bother correcting himself. You should also discount his political commentary appropriately. |
