The lowest-tech atom bomb

MSNBC ^ | 10/14/02 | By Richard A. Muller

[NY.SS-Bar9]

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.

Rest of story...

[taxcontrol]

Acutally, building an A-bomb is more of an engineering feat than nuclear science. One of the main difficulties is creating a shockwave that compresses the uranium core to sufficent pressure for a long enough duration to acheive critical mass.

One common means of doing this is to use a sphere of explosives, which concentrates the blast force to a point in the middle of the uranium core. The difficulty in this approach is the initial detonation sequence. If the sphere is not "primed" properly and the "blasting caps" do not go off in the right sequence, the shockwave will be asymetrical and will blow apart the uranium, failing to acheive the critical mass required.

This is why the US has been adverse to allowing very high power computers to be exported. Those computers can provide the horse power required to conduct these shockwave studies using known laws of physics. These computers can be used to create mathmatical models of what happens, and thus allow the design / engineering of the mechanics of the bomb to be vastly improved.

No, it is not an easy task. However, enough is known, even by a lay person such as myself, that I doubt Saddam would have much of a problem building a bomb if he had the materials.

[Mr. Bird]

Uranium bombs, unlike the more complex plutonium bombs, don’t require the tricky implosion method, but can employ the simple, reliable gun method

I don't know enough about this. Are you familiar with the "gun method"?

[AdamSelene235]

One common means of doing this is to use a sphere of explosives, which concentrates the blast force to a point in the middle of the uranium core.

I believe you are describing a plutonium implosion device not a u-235 device. U-235 is hard to refine but easy to detonate (one of the reasons the little boy design was never tested). Plutonium is easier to refine but harded to detonate. (we tested the fat man design before using it).

[Ronaldus Magnus]

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.

My guess would be more of a L.A./N.Y. double strike like we did to Hiroshima/Nagasaki. The only unknown would be how Israel would respond if they weren't hit.

[drjoe]

Actually you do not need an implosion device. The original bomb dropped on Hiroshima was a 'gun' device aka 'Little Boy'. Take an enriched U235 target and shoot another mass of U235 at it. The two come together and BOOM. The US was so sure that it would work that it was deployed and used without a full scale test. An experiment, 'Dragon', was carried out in a spare corner of Los Alamos. It consisted in dropping a subcritical mass of U235 [doughnut hole] through a subcritical mass [doughnut] of U235 and measuring the neutron flux, From this it was determined it would work and heigh-ho heigh-ho, it's off to Hiroshima we go. What would have happened had the hole gotten stuck in the doughnut is an exercise left to the reader. The rogue state developing a quick and dirty nuke does not need the problems associated with an implosion device.

[sharktrager]

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,” technologyreview.com, 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.

SMUGGLING URANIUM
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.

WORST CASE SCENARIO
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.

Target: Iraq?
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.

Richard A. Muller, a 1982 MacArthur Fellow, is a professor in the Physics Department at UC-Berkeley where he teaches a course entitled, “Physics for future Presidents.” He is also a faculty senior scientist at Lawrence Berkeley National Laboratory.

[Erasmus]

There is one big advantage to the gun device: It's simple.

There are two significant disadvantages to the gun device:

1. You need more fissile material, so it takes longer to make (starting from the day you get your enrichment plant running).

2. It's got to be big. Too big and heavy for a portable device, and very inconvenient for a clandestine one.

Of course, the above considerations apply for an actual fission bomb, not a 'dirty' scatter-radioactivity-with-TNT one.

[taxcontrol]

I believe you are describing a plutonium implosion device not a u-235 device

Actually the implosion device can be used for either.

[quietolong]

Read the book Dark sun info on book on this thread

Secrets, Lies, and Atomic Spies,.....Or... Joe McCarthy was more right than he ever knew

[ZeitgeistSurfer]

While everyone is looking at Iraq, Iran is on the verge of bringing its massive reactor at Bushehr on-line. This is the first step in the production of serious nuclear weapons. Iran is the greatest terrorist threat to the West, not Iraq. It is the country that has an al-Queda training camp. My sincere hope is that after GWB brings Saddam and his regime down, he turns his attention immediately to Iran

[AdamSelene235]

Actually the implosion device can be used for either.

Well, yes but precision timing is not required for a u-235 gun. This is the beauty of the device.

[null and void]

2. It's got to be big. Too big and heavy for a portable device, and very inconvenient for a clandestine one.

Too big for an ICBM. Several would fit in a shipping container...

[Cyber Liberty]

The "gun method" involves shooting a chunk of uranium through a tube and into a larger chunk of uranium, creating critical mass for the nuclear chain-reaction (fission).

The other type, the "implosion" device, uses a sphere of explosive lenses to compress a chunk of plutonium to achieve critical mass.

Both methods work. The sphere method has a more efficient yield, but the gun is simpler to design and build.

Hiroshima was a uranium gun weapon (Little Boy) and Nagasaki was a plutonium implosion weapon (Fat Man). The Trinity test explosion in New Mexico was identical to the device used over Nagasaki.

[boris]

"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,” technologyreview.com, Feb. 7, 2002). Nobody had anticipated that Saddam would use such a low-tech approach."

Don't calutrons require large quantities of energy? Does Saddam have the generating capacity to power them?

If so, take out his generators. I'm pretty sure he has no "civilian" nuclear power stations. Where does he get his electric power?...make them go away.

--Boris

[boris]

"While everyone is looking at Iraq, Iran is on the verge of bringing its massive reactor at Bushehr on-line. This is the first step in the production of serious nuclear weapons. Iran is the greatest terrorist threat to the West, not Iraq. It is the country that has an al-Queda training camp. My sincere hope is that after GWB brings Saddam and his regime down, he turns his attention immediately to Iran"

Perhaps Mr. Sharon will turn his attention to Iran. I don't think Israel will permit the Iranian reactor to come on line...given their treatment of the Iraqi reactor...

--Boris

[ZeitgeistSurfer]

Perhaps Mr. Sharon will turn his attention to Iran.

Agreed, Boris. It's a much greater threat to Israel. They need to take action very soon.

[AdamSelene235]

An experiment, 'Dragon', was carried out in a spare corner of Los Alamos.

AKA "Tickling the Dragon's Tail"

[Oztrich Boy]

I believe you are describing a plutonium implosion device not a u-235 device. U-235 is hard to refine but easy to detonate (one of the reasons the little boy design was never tested). Plutonium is easier to refine but harded to detonate. (we tested the fat man design before using it).

Actually plutonium is easier to detonate. The problem is that to avoid a "fizzle" a plutonium gun needs to bring its components together a lot faster and would have required a 30ft long bomb: too big for a B-29 bomb-bay, whereas the 10ft Little Boy fitted nicely.

Plus a gun requires 10X the explosive metal, and in '45 there wasn't enough plutonium for a single gun-device.

But U-235 can be used in implosion devices

Incidentally the only post 45 nuclear power to go gun was South Africa, which lead to "informed opinion" considerable overestimating SA's capablity. The size of the reprocessing plant said SA could produce enough U-235 for 5-10 bombs a year, which lead to an estimated stockpile of 100+, 155mm tactical nuclear shells, neutron weapons and all the lumber of a major nuclear power. Real situation was just 6 quite heavy gun-devices.

2. It's got to be big. Too big and heavy for a portable device, and very inconvenient for a clandestine one.

Not that big. Back c.1960 the size limit on implosion devices seemed to be >10" in diameter. So the first 8" tatical artillary shells were gun devices. maybe 300lb and 4ft long in the transport case, not lap-top size but reasonably portable.

Of course to go down to 155mm shell or 160mm mortar size, the weight of explosive metal gives a shell too heavy for the tube to fire, so you have to build a really tricky implosion device. Not for beginnners (see above re fears of South african tactical 155mm howitzers)

[Erasmus]

Actually plutonium is easier to detonate. The problem is that to avoid a "fizzle" a plutonium gun needs to bring its components together a lot faster and would have required a 30ft long bomb: too big for a B-29 bomb-bay, whereas the 10ft Little Boy fitted nicely.

Several corrections needed here. There's no such thing as a "plutonium gun" bomb. It is true that Pu239 needs to be assembled much faster, and that's precisely what makes an implosion design necessary. The Little Boy fit the B-29 nicely, but it was because they were able to reduce the size of the gun required below their initial estimates; in any event, it was a U235 device.

Plus a gun requires 10X the explosive metal, and in '45 there wasn't enough plutonium for a single gun-device.

It needs about 3 critical masses. Because the implosion design needs less than a critical mass (due to the compression of the material) the 10X figure is plausible.

It is true that in July '45 there wasn't enough Pu239 for a single gun-device there was never intended to be because they couldn't and weren't trying to make a Pu239 gun device; they were making an implosion device with it.

But U-235 can be used in implosion devices.

True, but irrelevant. If you can make U235, you make a gun device and obviate the technical challenges of an implosion device.

Incidentally the only post 45 nuclear power to go gun was South Africa, which lead to "informed opinion" considerable overestimating SA's capablity. The size of the reprocessing plant said SA could produce enough U-235 for 5-10 bombs a year, which lead to an estimated stockpile of 100+, 155mm tactical nuclear shells, neutron weapons and all the lumber of a major nuclear power. Real situation was just 6 quite heavy gun-devices.

And the reason they, or any nation, would go with a U235 gun design was to avoid the extraordinary expense of Pu239 breeder reactors, subsequent hot chemical processing, and the complexities of an implosion device.

And they pay for it with the need to make lots of U235 and in the jumbo size of the bombs that result.