Oralloy
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W88 comment
editI saw your comment here and would like some more detail on one note: "It was first used in the W47 and W56 warheads". I'm still trying to understand the physics here. To this untrained observer, it would seem a spherical implosion should result in higher core density for any given amount of explosive. I also thought that the reason for the prolate shaping was to allow it to fit into the "pointy end" of the conical RV's. I notice that later designs, like WE177 and B83 both appear to have spherical primaries. So what's the scoop here? Maury (talk) 11:50, 5 September 2008 (UTC)
- Maximizing core density would be desirable if you were trying to get the most efficient use out of the fissile material in an unboosted weapon.
- However, these designs are not so much concerned with making the most efficient use of the fissile material, but being as light as possible. They get a lighter design by using a weaker implosion system to compress a larger amount of plutonium.
- And in any case, in a boosted design, all you need to do is let the core get hot enough to ignite the deuterium-tritium gas. That causes a massive shower of 14 MEV neutrons that dramatically accelerates the fission chain reaction.
- The reason for the oblong design is because there is an innovation that allows for much lighter warheads, but this innovation apparently doesn't work with more than two explosive lenses to compress the fissile material. So instead of being surrounded by a bunch of smaller explosive lenses, there are two large explosive lenses on each side of the fissile material.
- The design is only intended to compress the fissile material very lightly -- just enough to ignite the deuterium-tritium gas (roughly a quarter kiloton or so). After that, the amount of D-T gas in the core determines what the ultimate yield of the primary is.
- One of the ways those dial-a-yield bombs select their yield is by varying the amount of D-T gas injected into the primary. The low yield (0.3 kt in the case of the B61 bombs) is the yield of the primary with no D-T gas injected in it.
- It's a bit tricky to get these designs exactly right, because you want to guarantee that the bomb will have zero nuclear yield if just one of the two explosive lenses goes off in an accident, and still get a yield hot enough to ignite the D-T gas when they are both set off. Oralloy (talk) 04:58, 20 May 2009 (UTC)