Some military analyst on CNN was saying how a dirty bomb (A bomb that uses the radioactive material as the weapon itself rather than the catalyst of an explosion) could fit in a suitcase. I was doubtful that one of any reasonable Osama-scale devastation could fit into a suitcase and the commentator’s credibility took a further hit when he said, “For instance, they might put a core of Uranium 235 around a bomb of TNT”
First off, isn’t Uranium 235 one of the most stable, non-radioactive of the radioactive substances? My understanding is that if you wanna fry someone get yourself the heavy metals that are products of fission, not the stuff that goes into it.
But more importantly, if you took a suitcase size bomb of (your choice of) radioactive material (say 30 gallons), over what range of effect could this have devastating consequences (choose your own level of devastation)?
Here’s some other threads asking a very similar question. And there are some rather recent ones also which I didn’t bother linking. They all point to these two.
http://boards.straightdope.com/sdmb/showthread.php?threadid=8478
http://boards.straightdope.com/sdmb/showthread.php?threadid=44233
Actually, those posts are still dealing with a fission bomb. This bomb’s purpose is to spread radioactive material, not use it as the explosive itself. It’s more like chemical warfare. If you spread enough radioactive material around it will cause sickness and render the place uninhabitable. Imagine taking a barrle of radioactive waste and strapping a stick of dynamite to it. It’ aint another hiroshima but it aint no holiday either.
The dirty bomb’s effectiveness would be in how far it could spread the ‘dirty stuff’. For a bomb that could fit in a suitcase I would guess maybe 100 yard radius (give or take). While certainly nasty it wouldn’t be all that bad as far as the ability to clean it up goes (it’d be a tough, nasty job but doable on that scale.
U235 is the stuff that bombs are made of. U238 is what most naturally occurring uranium is and it is generally harmless (i.e. holding it). IIRC I once saw that you could hold a hunk of U235 without any ill-effect (it was described as slightly warm to the touch). However, with most of these things, it’s getting it internally that is really dangerous. If you breathe it in you’re in far more trouble than just having it on your skin
Of course, the REALLY nasty stuff is Plutonium but that is harder to get (I think [sub]hope[/sub]).
To obtain a Controlled Surface Contamination Area (CSCA), you need 450 micro-micro curries (µµi) worth of Co[sub]60[/sub]-equivalent radioactive material per 100cm[sup]2[/sup]. That’s 4180µµCi per square foot. This will produce a level of radiation of 100 counts-per-minute (cpm) above background.
This is the minimal level of radioactive contamination necessary to call an area contaminated, not the amount that is life-threatening. Why this level? Because it’s the lowest level where you can definitively say that what you’re reading is from contamination. Anythng less than this is Less Than Minimum Detectable Activity (<MDA).
So, let’s say we wish to contaminate, say, an acre of flat ground. We’ll need 4180µµCi per ft[sup]2[/sup], times 43,560 ft[sup]2[/sup] gives a figure of 182µCi worth of Co[sub]60[/sub]-equivalent radio-isotope necessary to crap-up the ground. Now, lets see how much material might be necessary for this:
- Natural Uranium: Specifica activity = 0.67µCi/g :. 271 grams required.
- U[sub]234[/sub]: Specific activity = 6200µCi/g :. 0.029 grams (good thing U[sub]234[/sub] is damned rare!)
- U[sub]235[/sub]: Specific activity = 2.41µCi/g :. 75.5 grams required.
- U[sub]238[/sub]: specific activity = .334µCi/g :. 545 grams required.
Not a whole lot, hmm?
But wait…!
This is just the level that would require a clean-up crew equipped with fairly simple tools (vacuum cleaners with HEPA filters). What if we wanted to make this interesting? What would be required to cantaminate an area sufficiently to present a substantial risk, say, a dose rate of 1 REM/hr? (REM=Roentgen-Equivalent Man: That amount of radiation that does the same amount of biological damage as one Roentgen of Cobalt-60 gamma radiation)
Well, to start, our acre of flat ground is a planar source, so we can discount distance in our calculations. Next, at contact, 1095cpm > background = 1mRem/hr. That means that it takes 4927.5µµCi per 100cm[sup]2[/sup] or 45711µµCi per foot square to produce a dose-rate of 1mR/hr anywhere within our contaminated area, requiring 1994µCi, evenly distributed across the acre to produce 1mR/hr dose-rate. To bring this up to a reasonably threatening level of 1R/hr, you’d need roughly 20Ci, evenly spread.
That means:
- Natural Uranium: Specific activity = 0.67µCi/g :. 29,851 kilograms required.
- U[sub]234[/sub]: Specific activity = 6200µCi/g :. 3.23 kilograms required.
- U[sub]235[/sub]: Specific activity = 2.41µCi/g :. 8,299 kilograms required.
- U[sub]238[/sub]: specific activity = .334µCi/g :. 59,880 kilograms required.
This would be a bitch to clean up, but you could stand in the middle of it for two straight days, and the biological effect on you would be difficult to detect.
None of this takes into account how difficult it would be to design a delivery mechanism that would spread the material evenly, or the effects of random air currents, blast shadows, uneven distribution, buildings, and so on. It also deliverately ignores internal contamination, which is a whole new subject, and one I’m not competent to address.
This is a huge simplification of a complex issue, but gives a little grasp on the subject.
In short, provided no one were home when it went off, a truly dangerous “dirty bomb” would be difficult to build and deliver. It would be very large and heavy, and highly inefficient. A merely “scary” dirty bomb would be quite easy to design and deliver, but would be of nothing more that harrasment value, serving to scare people who don’t understand the subject, and maybe giving Green Peace a new cause.
If people were present when the bomb went “bang”, pretty much the contamination issues would be the same, but the health issue would be far more serious, albeit far less serious than if someone had, say, seeded the area with a few hundred pounds of Anthrax spores.
Note: U[sub]234[/sub] is extrordinarily rare, is a decay product, and isn’t a refined fuel used in any nuclear program. It is, however, a naturally occuring daughter of the deacy process, and is the reason natural Uranium is so much more active than pure U[sub]238[/sub].
As I feel compelled to contribute to any thread even remotely related to James Bond, I feel I must contribute here.
The bomb Golfinger uses in the film of the same name is a dirty bomb using some form of Cobalt as the dirty material. I’m not at home now, but when I get there, I’ll find exactly what kind. The bomb itself was the size of a street ventor’s hot dog cart.
Tranquilis–cool post; I agree with your
calculations, although I haven’t gotten out a calculator. The real problem is the one that you admit they don’t address—internal exposure. Contamination from a radiological weapon would, of course, be almost entirely loose, and the problem with loose contamination is the risk of ingestion and (worse) inhalation.
The thumbrule generally used for inhaled Co-60 is that
1 microcurie Co-60 retained in the lungs 1 day after
breathing gives you a committed dose (dose to the lungs
specifically, compared against a 50 rem per calendar year
dose limit) to the lungs of 6 rem, and a committed
effective dose (=dose equivalent to the whole body for
purposes of calculating risk of stochastic effects,
compared against 5 rem per calendar year NTE 3 rem
per calendar quarter dose limit) of 700 mrem, most of
which would take effect in the first year after exposure.
On the one hand, with a half-life of 5.27 years, Co-60 has
a far higher specific activity than any of the isotopes
of uranium. On the other hand, it’s a beta-gamma emitter, and hence far less damaging if taken internally than an alpha emitter (such as the isotopes of uranium discussed in your post) would be. (Alphas, with their high mass and charge, lose their kinetic energy very rapidly and are stopped by a dead layer of skin, but you don’t have a dead layer of skin on your innards.) In addition, if (as has been hypothesized), a radiological weapon used spent fuel rods, you have zillions of fission products (beta-gamma emitters with a wide range of half-lives) and their decay daughters in addition to uranium (and to some transuranics).
Net effect: Very bad news all round. Yes, people in anti-C’s
would be substantially protected from internal (not external, to which your calcs apply) exposure. I’ve never met anyone who wore anti-C’s anywhere he didn’t have to, though, and, of course, most people just plain don’t have them. I just pray we get bin Laden and everyone around him soon, and that he doesn’t have access to anything of the sort.
Thanks again for the excellent post.
Daniel
You’re most welcome, and welcome to the SDMB!
While the risk of ingestion or inhalation is severe, and I can’t effectively discuss internal dosage, I will note that a decent dust mask is effective protection against inhalation of particulate radioactive material, provided you un-ass the contaminated area pronto. External dose is far more manageable. You’ll need to toss your clothing, get one helluva close haircut, and take the Shower From Hell, but external decon is pretty straight-forward (and yes, I’ve been crapped-up before). Also, most particulates will settle quickly, save in conditions where there’s a fairly strong breeze, which will disperse the plume of material downwind, further dilluting the concentrations. This has the two opposed results:
- It’s much harder to clean up and more people (and larger area) are going to get expossed.
- Individual doses will be reduced significantly the further down-plume you go, and settled material will have far lower concentration.
Radiological weapons outside, unless you have a staggering amount of material to deliver, aren’t particulalry effective anti-personnel weapons, but may be reasonably effective mid-term area-denial weapons, provided you’ve enough material available and an efficient delivery mechanism.
OTOH, a radiological weapon indoors could be a horror. Imagine a handful of small-to-middling dust bombs going off in Penn Station at rush hour, or in a major enclosed arena during a football game. Ugly.
For a real-world scenario, read-up on Chernobyl. Mind you, Chernobyl put tons of material in the air, but it’s the best-studied real-world event available, and you can draw valid lessons from it.
For those of you wondering why Alpha particles are such a concern for internal dose: Alpha’s have a high energy, and should they reach unprotected tissue, they’re 20 times more damaging than a Co[sub]60[/sub] Gamma. Fortunately, a layer of dead skin is usually adiquate shielding against Alpha particles.
Actually the greatest damage may come from the unknown fear factor with the general population. Since the teeming millions don’t spend the time doing the homework as do some of the contributors to this thread, the fear factor may play the greater role.
After all, three anthrax letters killed five people, in a country of almost 300 million. Not to belittle those killed and those exposed, but what really did the most damage here? Fear.
Terrorism isn’t always about actual death and destruction. The fear of a terrorist attack also cause damage in many ways.
OTOH, we’ve already become blase about Anthrax. Yeah, I’m sure a small dustbomb would scare the crap outta lots of people, but I’m willing to bet that after the nine-day wonder was over, we’d get back to our routine pretty quickly.
This Washington Post story over at MSNBC has some good info on “dirty bombs”.