Monday, October 09, 2006

FIZZLED: North Korea bomb test, possible "predetonation" failure

Reuters: "Gary Gibson, senior seismologist at Australia's Seismology Research Centre, said a 4.2 magnitude quake would be the result of a one kiloton explosion."

"A U.S. intelligence source agreed that a preliminary examination of the data did not indicate a large blast or a series of explosions. But the source stressed that analysts were still working towards a definitive evaluation."

Back in 1991, DD attended a seminar on nuclear weapons presented at the Center for War, Peace and the News Media/Knight Center for Specialized Journalism on the campus of the University of Maryland.

The seminar furnished about thirty pounds of briefing books and unclassified scientific papers on the nuts and bolts of nuclear proliferation as well as the materials and methods of weapons production. There was no getting around the complexity of the subject matter and the necessity of coming to grips with the dry language of bomb-makers. [In other words, you might want to skip this.]

Speakers included scientists from the arms control agencies as well as the national labs.

One of the lecturers was J. Carson Mark, a former head of the Theoretical Division of Los Alamos.

In a paper entitled "Reactor Grade Plutonium's Explosive Properties," published by the Nuclear Control Institute, Mark reviewed some comments by J. Robert Oppenheimer, the father of the atom bomb, made one week after the first fission explosion at the Trinity site on July 16, 1945.

Oppenheimer, writing to General Leslie Groves, on use of the atomic bomb in combat, said: " . . . The possibility that the first combat plutonium Fat Man will give less than optimal performance is about 12 percent. There is about a 6 percent chance that the energy release will be under 5000 tons, and about a 2 percent chance that it will be under 1000 tons. It should not be much less than 1000 tons (1 kiloton) unless there is natural malfunctioning of some of the components."

Another week later, wrote Mark, Groves reported to the Chief of Staff: "There is a definite possibility, 12 percent rising to 20 percent, as we increase the rate of production . . . with the type of weapon used that the blast will be smaller due to detonation in advance of optimum time. But in any event, the explosion should be on the order of thousands of tons."

"Evidently both Oppenheimer and Groves were referring to what will be identified in the following discussion as a 'fizzle yield'; that is, the smallest nuclear yield this particular device could provide. They do not state a value for this yield, but in view of their saying 'it should not be much less than 1000 tons' it may be presumed that they were thinking of some value like 700 tons or so."

Mark then goes into a discussion on the probabilities of a the entire device surviving long enough without a spoiling (preliminary to the main act) chain reaction occuring that would cause the weapon to blow apart before reaching its theoretical yield.

Predetonation resulting in a fizzle, which certainly seems to pertain to North Korea's test, depends on a number of factors: how well the bomb design is manufactured, how fast the bomb assembles into supercriticality, the bomb mechanism's size, weight, composition and density, and, most importantly, the number of background neutrons from what the weaponeers call spontaneous fission within the workings of it.

Mark described this problem further in another paper called "By What Means Can Terrorists Go Nuclear?"

". . . [T]here is a moment when the [bomb's] fissile material becomes critical (projectile still on its way to its destination [in a gun-type weapon], or only a small part of the material compressed [in an implosion-type weapon]) and the time it reaches its intended state. During this interval, the degree of supercriticality is building up toward its final value. If a chain reaction were initiated by neutrons from some other source during this period, the yield realized would be much smaller --possibly a great deal smaller -- than the nominal yield. Such an event is referred to as preinitiation (or sometimes predetonation).

Further, Mark writes, "If the [bomb's] assembly velocities (of the projectile or material driven by an implosion) are quite low, the earliest possible preinitiation could lead to an energy release (equivalent weight of high explosive) not many times larger than the weight of the device."

Other parts of the discussion on bomb design obstacles, also presented at the seminar, indicated that yields lower by a factor of ten in crude designs can be indicative of fizzles. What information has been published on the North Korean test falls into this range.

Summarized, there are certain number of things that can go wrong when firing your first atomic bomb, particularly when using a crude design. And one might expect to see them from a weird and crazy hermit nation, like North Korea, endeavoring to enter the nuclear club.

Tuesday: The Los Angeles Times employed an expert to touch upon the issues addressed in this discussion: "The lower yield could be a result of bad luck or bad design," said Michael Levi, at the Council of Foreign Relations, to the Times.

And, "The fizzle of a 15-to-20 kiloton weapon would be a kiloton or two, added Owen Cote, associate director of a security program at MIT.

In 1991, the nuclear weapons seminar presented at the University of Maryland's Knight Center was designed specifically for journalists. It was well ahead of its time in its aim that reporters be brought up to speed through immersion in the technical details of the subject. One of the purposes of it was to impart enough training so that the usual experts would not be required to hold their hands so much on the nuclear proliferation beat.

Also in, discussion on dud blast at Defensetech.
An earlier summary from the Reg.


Anonymous Anonymous said...

Kim Jong Il specifically instructed the scientists to produce a low yield so as not to shake sacred Paekdu mountain unnecessarily.

The low yield was due to Kim's request, and no one disobeys him in North Korea.

6:25 PM  
Anonymous Anonymous said...

Pu 239 as opposed to Pu 240. The latter emits naturally and tends to "poison" the process...old stuff. The longer you "cook" the Pu the more 240 you get. Power reactor by product 240 is not good "poot"

My "bet" is that they know what they're doing, but it's just a bet.

9:40 PM  
Anonymous Anonymous said...

Never mind what the North Korean Leader has done, just put him back into the stone age for good...

6:41 AM  
Anonymous Anonymous said...

I was under the impression that miniturization was difficult and required lots of R&D. Is the same thing ture of A-bombs or does someone like Il just order one up at any size? Many experiments fail on the first try. I think that why its called research and not just search. How long until they try again?

8:49 AM  

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