Nuclear Friday: A Piece of Starlight

Just what is a hydrogen bomb and how does it differ from an atom bomb? The terms as they have entered popular usage can be quite confusing. Basically, “atom bomb” generally refers to fission devices which release energy by turning heavy atomic nuclei into lighter ones. These are the kind of bombs developed by the Manhattan Project and used against Japan in WWII. The term “nuclear bomb” is regarded as more accurate than “atomic bomb” because all of chemistry is based on interactions at the atomic level. Chemical interactions are atom-on-atom, but they are interactions between whole atoms and occur between the outer electrons of atoms. Fission is something that happens inside individual atoms, thus “nuclear” is more accurate than “atomic”.

Likewise, “hydrogen bomb” is somewhat misleading. Yes, hydrogen is involved, and that makes a big difference, but many other things are going on too. The more accurate term is “thermonuclear device”. This is because the heat and pressure from one nuclear device, a fission bomb, is used to initiate a second type of nuclear reaction, fusion, which is much more energetic. Fusion is a second type of nuclear reaction, the joining of two atomic nuclei into a new atom. Fusion does not “want” to happen. Atoms repel each other unless they can react at the level of their outer electrons, and if you push past that repulsion, the intensely concentrated positive charges of the atomic nucleus forestall any interaction. But in the crushing gravity of the core of a star, fusion is possible. And fission reactions can briefly get hot enough to initiate fusion. They say fusion is harvesting the power of the stars. That’s not entirely true. The first thermonuclear device, Ivy Mike, replicated a fusion reaction that is only a small part of what powers stars like our Sun. Just one piece of starlight.

Edward Teller was thinking about fusion and huge bombs even while he was working at Los Alamos. After WWII ended, Teller was always thinking about bigger weapons, including Doomsday Devices. Teller is usually thought of as one of the “bad guys” of US nuclear weapons research. I think this is unfair. Survivor guilt from The Holocaust can change people.

Teller called his proposed bomb “Super”. A large fusion bomb at least a thousand times stronger than the first atomic bombs. Truman approved a study project, and here’s how it worked out:

I chose this video because it has the most detailed animation of the interior of the Mike device at Operation Ivy. But it is terribly misleading. The video mentions many elements being created and suggests that these were created by fusion. NO!  Ivy Mike created nothing but helium and neutrons in its fusion reactions. The filmmaker has defended his assertion in the comments on Youtube and cited Richard Rhodes who is interviewed in this video as a source. I think he misinterpreted Rhodes. The wide range of elements in the Mike test were created by neutron bombardment of the uranium tamper around the Mike secondary, and possibly also by neutron bombardment of the coral rock at Enewetak.

Ivy Mike was a dirty test. About 77% of the energy of the blast came from U-238 fission in the uranium jacket. There were five tons of refined natural uranium in that jacket. A small amount came from the boosted fission primary, and about 21% came from fusion. Not much of the jacket actually underwent fission, so fallout was intense. Two new elements were discovered in the fallout.

Ivy Mike was pretty impressive for 1952, but not a viable weapon. In the USSR, physicists called Mike a “Thermonuclear Installation”. The US would make a weaponized device based on Mike nicknamed “Jughead” to be carried on a modified B-36. It needed to carry a cryogenic freezer plant to replace leaking deuterium. Hardly a viable weapon. The USSR took a different path to thermonuclear weapons, and the US caught up pretty fast. Both would have viable thermonuclear bombs around the same time.

NEXT WEEK: Dry Fusion and a mishap for the USSR, and near Political Disaster for the US.

Research video:

Here’s a video released by Eisenhower based largely on footage the Truman administration prepared for the 52/53 transition.

 

 

 

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