06 January 2016

I am Calling a Boosted Fission Device

The DPRK has claimed to detonate a Hydrogen Bomb, but the seismic evidence would indicate otherwise:
The bold claim by North Korea on Wednesday that it had detonated a hydrogen bomb appeared to fizzle under the intense scrutiny of U.S. physicists and nuclear weapons experts.

The explosive power detected by earthquake sensors around the world was much weaker than would be expected from a hydrogen bomb, experts said.

“It was not very big,” said Philip Coyle, the former director of nuclear weapons testing at the Nevada Test Site and a longtime U.S. national security official.

An exhaustive investigation into the test, including sampling air for telltale radioactive particles and studying seismic shock waves, will take weeks. The analysis is likely to confirm the size of the detonation, the type of radioactive fuel it used, how the fuel was produced and the sophistication of its design.

U.S. experts initially estimated the power of the underground explosion was as small as 6 kilotons, less than the atomic bomb that the U.S. dropped on Hiroshima in World War II.
Some basic technical information: There are 3 types of nuclear weapons:
Fission bombs use Uranium or Plutonium to create a bomb.

Boosted fission weapons use small quantities of the isotopes of Hydrogen deuterium and tritium and achieve a minimal amount of fission, but allows for a greater percentage of fusion fission for a given amount of material because the small amount of fusion emits a large number of neutrons, increasing the reaction.

Among other things, a boosted fission weapon can be a lot smaller than a pure fission device.

Thermonuclear (Teller-Ulam) weapons typically have three stages:
  • A boosted fission primary which has a mirror to focus its energy on
  • A mixture of deuterium and tritium which fuses on a large scale, and releases neutrons which
  • Initiate fission in a depleted (U-238) jacket
A pure fission weapon is typically in the 20 kiloton range.

A boosted fission weapon weapon could go up to an upper limit 1 megaton.

The first thermonuclear weapon, "Mike" was 10 megatons, and the largest one ever detonated was the Soviet Tsar Bomba, which was designed to achieve 100 MT, but only achieved 50 MT because the depleted uranium jacket was omitted to reduce fallout.

Theoretically, there is no limit on the size of a Teller Ulam device.

So, on to the analysis.

The first thing to note is that, much like making watches, it is tougher to make a small bomb than it is a large one, so it is highly unlikely that any true thermonuclear weapon would be under a megaton.

Second, it is likely that the DPRK is looking at miniaturizing their weapons, and a boosted fission device would achieve this.

Third, for one to have a practical thermonuclear weapon, you need to have a boosted fission first stage, otherwise, you end up with something like "Mike" which weighed over 80 tons. (Mike used a boosted fission trigger, it was just f%$#ing huge as a result of being the first such device, the fact that it used liquid deuterium, and the associated support and measurement equipment).

So, my not so expert opinion:
  • It's a big deal, but applies to any nuclear test.
  • It was probably a test of a boosted fission device.
  • It was likely a fizzle, as the seismology shows a relatively low yield.
So, yes, this is a big f%$#ing deal, and I would suggest that a formal exchange of ambassadors and diplomatic recognition, which was agreed to in 1994, might be a good counter move.

In the mean time, I am sure that China, Russia, the US, Japan, and South Korea are analyzing the information, and sampling the air in the region to get more specifics.


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