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Lost Images from the 1945 Trinity Nuclear Test Restored

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Re: Lost Images from the 1945 Trinity Nuclear Test Restored

#71

Post by generuso »

wat10000 wrote: post #58
libraryofbabel wrote: post #52

Earlier quoted context omitted.

You’re thinking of the other bomb, the U-235 one, which they didn’t test at Trinity and which was dropped on Hiroshima. That is two separate pieces of Uranium that are slammed together to create a critical mass. The Pu-239 core was a single sphere of metal. It was subcritical until you compress it down with a spherical implosion from explosive charges all around it (from the size of a grapefruit to the size of a lime…

The gun-type bomb (where a subcritical mass is shot into another subcritical mass) is very simple to build once you have the materials to do it. They didn't think it needed a test since it was pretty obvious that it would work. The implosion design is tricky. You need to arrange and detonate the explosives precisely to compress the core evenly from all sides, otherwise it shoots out the side or otherwise doesn't go b…

It is all true, but one needs to take into account that because of the different properties of the materials, the critical mass for uranium-235 is intrinsically much greater than that for plutonium-239.

For a bare sphere, it is about 10 kg for plutonium and 50 kg for uranium.

Re: Lost Images from the 1945 Trinity Nuclear Test Restored

#72

Post by jltsiren »

technothrasher wrote: post #62

I went and visited the Trinity site a bunch of years back during the open house day in October. They gave us a little pamphlet at the gate that said there was no radiation danger to worry about. Then we passed signs along the way to the site saying things like, "don't eat, don't drink, don't apply make-up, don't rub your eyes." The mixed messages didn't exactly inspire confidence. You can see the few little bits of t…

I remember similar warnings from when I visited Chernobyl ~20 years ago. The ambient radiation exposure was not that different from the average flight, but there could be some actual risks if you accidentally ingest radioactive dust.

Re: Lost Images from the 1945 Trinity Nuclear Test Restored

#73

Post by ghaff »

libraryofbabel wrote: post #36

I used to teach a class on the history of contemporary science (WW2-present) and I started the class with Trinity. There’s no other moment better. We know how it turned out, but the people there waiting for the test did not know how it would turn out. The bomb might not have worked. Or it might have ignited a fusion reaction in the atmosphere and destroyed the world. Hans Bethe had sat down and done the calculations…

It was probably all pretty silly but there were a few probably-not-all-nutcases that were concerned about the LHC causing something horrible.

Re: Lost Images from the 1945 Trinity Nuclear Test Restored

#74

Post by generuso »

hydrogen7800 wrote: post #70
libraryofbabel wrote: post #52

Earlier quoted context omitted.

You’re thinking of the other bomb, the U-235 one, which they didn’t test at Trinity and which was dropped on Hiroshima. That is two separate pieces of Uranium that are slammed together to create a critical mass. The Pu-239 core was a single sphere of metal. It was subcritical until you compress it down with a spherical implosion from explosive charges all around it (from the size of a grapefruit to the size of a lime…

>(from the size of a grapefruit to the size of a lime) Whoa. Its hard to imagine you could have enough conventional explosives to compress a dense metal by ~10x (?). You'd need some serious containment to direct that energy inward rather than outward. I suppose I have some reading to do.

Plutonium was compressed about two-fold by volume.

There is a story about it. When they first brainstormed the ways to make the bomb, even before Los Alamos, in 1942, one of the several ideas was to use explosives to throw smaller pieces of material together, to make the super-critical mass. This was dismissed as too imprecise, but it was still listed in the April 1943 as one of the possibilities in the Los Alamos Primer, which was the orientation booklet for the scientists joining the project.

One of the scientists, Seth Neddermeyer, fell in love the the idea and talked the bosses into letting him try it. He consulted with the explosives experts in Pittsburgh and started some crude preliminary experiments.

When von Neumann was told about these experiments in October 1943, he immediately pointed out what when the pieces of metal slam together at a high velocity in the center, this creates extremely high pressures. Teller then remembered that at such pressures, iron in the Earth's core becomes slightly compressed. They instantly realized that compression makes the exponent in the chain reaction greater, and that this is a new way to make the bomb. They explained the idea to Oppenheimer, and he pivoted the project to the new method.

This did not work. The material did not assemble into a neat ball, but was just making a mess. But Robert Christy, the guy who was making the calculations for this, realized in September 1944 that the slamming of the pieces together at high velocity was not strictly essential, and that a solid ball of metal could also be compressed by an inward going shock, although not as efficiently. Because this was guaranteed to work, this was chosen as the design for the "Gadget".

Ironically, Seth Neddermeyer, who was instrumental for this to happen, has never accepted that the metal could compress.

April 1943 Robert Serber "Los Alamos Primer" https://upload.wikimedia.org/wikipedia/commons/9/9c/Los_Alam...

Interview with Robert Christy where he recalls the invention of the solid core https://www.youtube.com/watch?v=Ez45QEMI5CA&list=PLVV0r6CmEs...

Re: Lost Images from the 1945 Trinity Nuclear Test Restored

#77

Post by Finnucane »

q1bz2p wrote: post #25
Finnucane wrote: post #24

I keep a small collection of nuclear testing-photography related books, looks like I'm going to have to add this one.

Would love to know your complete list. My copy of 100 SUNS has lived on my coffee table(s) for decades. https://www.michaellight.net/suns-intro

It is, as I say, a small list. 100 Suns, of course. Also, American Ground Zero (do not try to read all at once), At Work in the Fields of the Bomb (interviews and portraits of Los Alamos and Livermore weapons scientists), and How to Photograph and Atomic Bomb. I might also include the souvenir book I got at the Nevada test site when we went on the bus tour in 2003.

Re: Lost Images from the 1945 Trinity Nuclear Test Restored

#78

Post by gpm »

libraryofbabel wrote: post #36

I used to teach a class on the history of contemporary science (WW2-present) and I started the class with Trinity. There’s no other moment better. We know how it turned out, but the people there waiting for the test did not know how it would turn out. The bomb might not have worked. Or it might have ignited a fusion reaction in the atmosphere and destroyed the world. Hans Bethe had sat down and done the calculations…

> Or it might have ignited a fusion reaction in the atmosphere and destroyed the world

Someone's got to explain to me how this was even remotely plausible.

We've had orders of magnitude more energetic events in earth's history that they would be aware of (dinosaur slaying asteroid for instance). These didn't manage to destroy the earth by turning the atmosphere into a fusion reactor. Surely they were aware of this.

So was the theory that neutrons are somehow special in a non-thermal way for causing fusion (not fission). And specifically that a concentrated neutron burst could somehow set off a chain reaction? And I guess that [edit: solar] neutrons weren't concentrated enough to cause this even at a detectable level?

Re: Lost Images from the 1945 Trinity Nuclear Test Restored

#80

Post by voidmain »

gpm wrote: post #78
libraryofbabel wrote: post #36

I used to teach a class on the history of contemporary science (WW2-present) and I started the class with Trinity. There’s no other moment better. We know how it turned out, but the people there waiting for the test did not know how it would turn out. The bomb might not have worked. Or it might have ignited a fusion reaction in the atmosphere and destroyed the world. Hans Bethe had sat down and done the calculations…

> Or it might have ignited a fusion reaction in the atmosphere and destroyed the world Someone's got to explain to me how this was even remotely plausible. We've had orders of magnitude more energetic events in earth's history that they would be aware of (dinosaur slaying asteroid for instance). These didn't manage to destroy the earth by turning the atmosphere into a fusion reactor. Surely they were aware of this. S…

I think the tiny size of a nuclear weapon and very short interval of nuclear reaction before "disassembly" mean that even though the energy release is small compared to an asteroid impact the temperatures are probably much higher.

(I'm not an expert, though, this is a guess)

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