The discussion centers on the confidence of scientists involved in the first nuclear explosion test, specifically the Trinity Test conducted on July 16, 1945. Participants expressed complete certainty that a self-sustaining reaction in the atmosphere would not occur, supported by investigations and reports, including the 1946 Los Alamos report by Konopinski, Marvin, and Teller. The conversation also highlights the Castle Bravo test of 1954, which unexpectedly yielded 15 Megatons, illustrating the complexities and risks associated with nuclear testing. Overall, the scientists' confidence stemmed from extensive theoretical understanding and prior experiments, despite some historical oversights.
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Completely certain.Robert P said:How sure were those involved with the first nuclear explosion test that there wouldn't be an unanticipated reaction of the explosion continuing beyond the material intended? I.e. that the Earth wouldn't go up in a ball of fire, the scientist's last utterance wouldn't be "Oops..."?
It was just something that occurred to me contemplating the topic. "Well, the reaction is *supposed* to happen a certain way, whaddya say guys - throw the switch and see what happens?" And all those rockets weren't supposed to splatter on the launch pad either.russ_watters said:Completely certain.
[Edit] You might be referring to this:
https://www.insidescience.org/manhattan-project-legacy/atmosphere-on-fire
There was a concern based on the temperature that the fission device would generate. However, the atmosphere is too thin and unconstrained such that fusion cross-sections are way to low, and scattering and radiation would disperse the energy.caz said:Here’s the 1946 Los Alamos report “Ignition of the Atmosphere with Nuclear Bombs” by Konopinski, Marvin and Teller.
Follow-up question: in the early days, how certain were they that the bombs would work? Were there any unsuccessful tests? My understanding was that they were highly certain and the bombs were exceptionally reliable.Astronuc said:The Trinity Test demonstrated that a self-sustaining reaction in the atmosphere would not occur, as did the deployment of nuclear detonations over Hiroshima (gun-type, enriched U) and Nagasaki (implosion-type, Pu), as did subsequent atmospheric tests by US, Russian, UK, China and France.
Not of bombs. They were so confident about the gun-type design that the didn't even try to test it prior to dropping the Hiroshima bomb. They ran the Trinity test, which was successful, because the implosion design had some tricky issues regarding timing and they wanted to make sure that their solutions for that, which had nothing to do with the nuclear physics involved (they knew the criticality requirements for plutonium quite well from experiments) but were just traditional, though intricate, bomb detonation design, would work well enough to get a reasonable nuclear yield.russ_watters said:in the early days, how certain were they that the bombs would work? Were there any unsuccessful tests?
Of course the this begs mention of the Castle Bravo test which, while not a planet-ending event, did provide a yield of 15 Megaton which was three times the expected result. This resulted in at least one death and imperiled the near observation team.anorlunda said:The short answer is that they thought of that possibility. They investigated it. They concluded that it can't happen.
As per my post #9, yes, they were. But it's worth noting that a big part of the reason they were is that they ran some experiments that, today, we would consider foolhardy, such as the "tickling the dragon's tail" experiments. Looking back, I think the Manhattan Project and its immediate follow-ons after the war were quite lucky that there weren't more serious accidents. (I say "more" because the number was not zero: see, for example, the criticality accident that ended up killing Louis Slotin.)russ_watters said:My understanding was that they were highly certain and the bombs were exceptionally reliable.
Trinity test (July 16, 1945) was the first and only test of a device before deployment of weapons at Hiroshima (August 6, 1945) and Nagasaki (August 9, 1945). PeterDonis in post #9 explains quite well the thinking at the time.russ_watters said:Follow-up question: in the early days, how certain were they that the bombs would work? Were there any unsuccessful tests? My understanding was that they were highly certain and the bombs were exceptionally reliable.
I do remember stories of tests that didn't achieve expected yield, and those that produce more and much more.hutchphd said:Of course the this begs mention of the Castle Bravo test which, while not a planet-ending event, did provide a yield of 15 Megaton which was three times the expected result. This resulted in at least one death and imperiled the near observation team.
The Castle Bravo test was singular because there was a truly fundamental theoretical omission in the nuclear physics. This was the first test using Lithium Deuteride and before the Castle Bravo nuclear weapons test in 1954, it was thought that only the less common isotope 6Li would breed tritium when struck with fast neutrons. The Castle Bravo test showed (accidentally and emphatically) that the more plentiful 7Li also does so.Astronuc said:I do remember stories of tests that didn't achieve expected yield, and those that produce more and much more.
That's certainly in the "Oops" realm.hutchphd said:anorlunda said:
The short answer is that they thought of that possibility. They investigated it. They concluded that it can't happen.
Of course the this begs mention of the Castle Bravo test which, while not a planet-ending event, did provide a yield of 15 Megaton which was three times the expected result. This resulted in at least one death and imperiled the near observation team.
Think on a broader scale. How can you quantify the risk of the unknown in any experiment in any field? If you and your mate spawn a new embryo, what is the risk that you create a mutant that will wipe out other people? You say, "Zero risk." Someone else says, "Prove that." That is not a rational discussion.Robert P said:I wonder how sure were they that for example there wasn't a threshold beyond which their notions of why it shouldn't happen might not hold true.
But it does lead directly to Donald Rumsfeld. Was the Castle Bravo incident a "known unknown" or an "unknown unknown" ?anorlunda said:That is not a rational discussion.
I had to go look that up.hutchphd said:But it does lead directly to Donald Rumsfeld. Was the Castle Bravo incident a "known unknown" or an "unknown unknown" ?
Clearly, the OP is asking about the unknowns unknowns in the first atomic explosion.This has led me classify unknowns into one of the following two types: 1. known unknowns (expected or foreseeable conditions), which can be reasonably anticipated but not quantified based on past experience as exemplified by case histories (in Appendix A) and 2. Unknown unknowns (unexpected or unforeseeable conditions), which pose a potentially greater risk simply because they cannot be anticipated based on past experience or investigation. Known unknowns result from recognized but poorly understood phenomena. On the other hand, unknown unknowns are phenomena which cannot be expected because there has been no prior experience or theoretical basis for expecting the phenomena.
Robert P said:I wonder how sure were they that for example there wasn't a threshold beyond which their notions of why it shouldn't happen might not hold true.
It is my (very rudimentary) understanding that the processes involved with 7Li required extremes in T and P that had simply not been previously accessed. I believe that natural Li is nearly 90% 7Li and so this was not a trivial error. I believe it was an unknown unknown and not simply an oversight.anorlunda said:But I fail to see any connection between Castle Bravo and the OP's question.
I just watched a video about it - it impacted thousands of islanders and the crew of a fishing ship resulting in illness, disease and death.hutchphd said:Of course the this begs mention of the Castle Bravo test which, while not a planet-ending event, did provide a yield of 15 Megaton which was three times the expected result. This resulted in at least one death and imperiled the near observation team.