So the little boy had cobalt components. Did he say if it was the tamper that contained it? Do you have his book? According to Agnew it’s in John’s book. I don’t have it to look...
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I don't recall seeing any explanation of why they used WC in LB instead of U, though they also studied U. My guess (half-memory?) is that they were worried about excess neutrons in the core causing predetonation possibilities. U has a real background neutron rate, WC does not.
When you are assembling multiple crits in an inefficient way, you want to make sure the thing doesn't really start until it is supposed to start. The U-235's surface was coated with cadmium to absorb stray neutrons as well.
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Here's a nice bit from a 1944 report. Same report notes that they wanted to play with the cobalt levels to see how it affected the ductility of the tamper, but that they wanted to be conservative with what was understood. https://www.osti.gov/opennet/servlets/purl/16135471.pdf …pic.twitter.com/ZTcDbIsRvT
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A slightly later 1944 doc indicates the different levels of Co they experimented with for the gun program (3, 6, 9%). From what I can tell, John thinks it was 6% based on an experimental report, not I think, bc something said the final version was 6%. https://www.osti.gov/opennet/servlets/purl/16135456.pdf …pic.twitter.com/wLR0cdBXVy
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Unrelated, but interesting: in a report on "tests we should do to make sure LB is safe-ish," one of the fears is that it could go critical from having lots of (water-filled) people near it. How to test the limit? Gather lots of people, see what happens! https://www.osti.gov/opennet/servlets/purl/938436.pdf …pic.twitter.com/AADzL5JM6P
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I love the next line about “well, water immersion will give an upper limit also” -
I mean it's not like water immersion of fissile material can cause problems...pic.twitter.com/UfoQeooTOY
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Isn't that the basis of the early "water boiler" experiments
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The water boiler was an actual reactor design (if a simple one). This was just them putting HEU in water to make measurements — much less thought seems to have gone into the criticality dangers.
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It was a cadmium impregnated sabot that was stripped off as it assembled was my understanding? The declass decisions suggest that that structure continued to be used in the gun assembled artillery weapons (or at least one of them) as well.
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I don't think there was a sabot in the final LB design. The pieces of the HEU themselves were electroplated coated with cadmium, several documents indicate, e.g. —pic.twitter.com/FHIwMvlfUx
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Today I learned!
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So did I, great stuff!
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This particular document was one I managed to find for JCM and he was very pleased by, because the "inside/outside" geometry described basically only works with his hollow-projectile idea of LB (the projectile does not have an "inner cylindrical surface" unless he is right).
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And I felt particularly clever realizing that it inadvertently gave away a lot of geometrical information about the design, just with simple inside/outside terminology, probably without the redactor realizing it. :-)
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