The Lowest-Tech Atom Bomb


by Richard A. Muller

Technology for Presidents

from Technology Review Online

October 11, 2002


Saddam Hussein had us completely fooled, once. Prior to Desert Storm in 1991, we had monitored and embargoed his importation of high tech centrifuge and laser equipment that could be used to make highly-enriched uranium (HEU). material that -- once you have it -- makes building an atomic bomb easy. After Saddam's defeat, inspectors found that he had spent an estimated $8 billion building calutrons, ancient devices (from the 1940s) that Ernest O. Lawrence had used to make HEU for the Hiroshima bomb. (See 'Springtime, Taxes and the Attack on Iraq,', Feb. 7, 2002). Nobody had anticipated that Saddam would use such a low-tech approach.


We won't be fooled again. U.N. weapons inspectors, if they are ever readmitted to Iraq, will search specifically for evidence of calutron construction. A calutron is a magnetic separator that makes HEU by taking raw or partially-purified uranium and concentrating the rare and more easily fissionable isotope U-235, which makes up only 0.7% of natural uranium. For a uranium bomb, this separation is the hard part; the weapon design is easy. According to the International Atomic Energy Agency, 25 kilograms is a 'significant amount' of HEU -- an amount, they say, 'in respect of which the possibility of manufacturing a nuclear explosive cannot be excluded.' If Saddam has this much HEU, he essentially has a nuclear weapon.


It takes nearly two tons of uranium ore, run efficiently through calutrons, to separate 25 kilograms of HEU. Most analysts believe it unlikely that Saddam has enriched this much uranium. When his previous calutrons were discovered and destroyed, they hadn't even been finished. Thus, he probably doesn't have sufficient HEU -- yet -- for a nuclear weapon.

Unless he is using an even lower tech approach: smuggling. In 1996, Swiss police in Zurich arrested a Turkish national and confiscated 12g of HEU. They determined that the material had been obtained in either Kazakhstan or Russia. The trail was hot, and four days later Turkish police arrested the remainder of the smuggling ring, with 1.2 kilograms of HEU in their possession. 


Why worry?  A kilogram is not a significant amount. Even smugglers need a supplier. Is there reason to think that a substantial quantity of HEU is available?


Consider what we learned in Kazakhstan. After the Soviet breakup, a large amount of HEU was left in the republic. To qualify for the benefits of the 1968 Nuclear Non-Proliferation Treaty, the government of Kazakhstan gave its stockpile to Russia for dilution and safekeeping in 1995. A year later, much to their embarrassment, the Kazakhstanis  reported the discovery of another 205 kilograms of HEU. It had never been listed as missing, and no one was looking for it; it just turned up. The bookkeeping of the former Soviet states makes Enron's accounting look scrupulous. How much more HEU is still out there, undocumented? Nobody knows. That's why we worry.


If you have your hands on a few grams of U-235, then Saddam is almost certainly your best customer. Assuming he had spent $8 billion on calutrons to try to produce 25 kilograms, then his cost was $320 million per kilogram. That is over 12 times the market value of gem-quality diamonds.


In November 2001, police in Istanbul seized about one kilogram of HEU that smugglers tried to sell to undercover agents for $750,000. Why were the smugglers asking for so little? Maybe they didn't know their own worth. Or -- here's a chilling thought -- maybe there is competition, and it is a buyer's market.

True, the Turkish police did intercept the HEU. But experience with drug smuggling shows that we catch only a small fraction of what is smuggled. This suggests that Saddam might even now have many kilograms. Suppose he has a significant quantity of HEU -- what could Saddam do? Uranium bombs, unlike the more complex plutonium bombs, don't require the tricky implosion method, but can employ the simple, reliable gun method. This is all explained in detail by one of the original designers of the Hiroshima bomb, Robert Serber, in his book, The Los Alamos Primer. Serber says that the critical mass for a uranium-tampered bomb is 15 kilograms; the Hiroshima bomb, which used three critical masses, was finished two years and four months after the Los Alamos laboratory opened. It was considered so reliable that it was never tested before it was used.


Fortunately for Saddam, Serber's book gives equations and tricks (such as the use of neutron-reflecting tampers, or casings) that apparently eluded even Heisenberg, the leader of Nazi  uranium project. What's more, Saddam's designers have been at work for over a decade, while waiting for their supreme ruler to obtain the HEU.


But Saddam has no missiles that could reach the United States. What could he do with a few small bombs?


Unlike weapons-grade plutonium, (which is typically contaminated with Pu-240, a spontaneous neutron emitter), U-235 is difficult to detect without active probing, as with a thermal neutron source). It emits alpha particles and some energetic gamma rays, but these can be shielded with lead. This makes HEU relatively easy to smuggle. The easiest way to get a bomb into the US is probably in a shipping container. We wouldn't detect it unless we were tipped off about where to look.


Let's imagine a bad case. Saddam sets off a bomb in Washington D.C. Unlike the designers of the Hiroshima and Nagasaki bombs, he derives great pleasure from mass death. Unlike bin Laden, he takes credit immediately for his terrorism. He announces that he has additional weapons, and that if the U.S. retaliates, he will start setting them off in major U.S. cities.


Last month, British Prime Minister Tony Blair announced that Saddam has been seeking to buy uranium from African countries (which produce 20 percent of the world supply). This is, of course, illegal, since he has no reactors, and no legitimate use for large amounts of uranium. But why would he do this, if he already had HEU? Doesn't his interest prove that he is, at worst, rebuilding calutrons?


No. If I were Saddam, I would import uranium in order to give that impression, to lull the U.S. into a false sense of security, into believing that there is plenty of time. Let's not make that same mistake twice -- of assuming that Saddam is doing it in the obvious way.


What hope have we? Well, maybe the Kazakhstan case was a fluke, and there is not a significant quantity of HEU available. Maybe most of the reported smuggling cases were actually fraud, or CIA sting operations designed to find out who is buying, and there is no real HEU to purchase. (A widely-reported seizure on September 28 in Turkey, 250 km from the Iraqi border, contained no real uranium.) Maybe Saddam has already made a bomb, but hasn't yet figured out how to sneak it into the U.S. Maybe Serber deliberately put plausible but misleading information into his book that would foil and delay a terrorist, and make an untested bomb into a dud.


We can hope.