Oppenheimer Movie Review

[Sal Ammoniac]

Fritz Haber was a national hero in Germany between the world wars and Adolf Hitler personally offered to make an exception to the anti-Jewish laws for him but he turned down that offer and wanted to maintain his Jewish identity.

He did convert to Christianity, so perhaps his Jewish identity really wasn't that important to him.

[Sal Ammoniac]

The movie sort of treated the bomb like oh it really worked.

That was the plutonium implosion bomb. Implosion was required for the plutonium bomb because plutonium had too high a spontaneous fission rate to use the gun mechanism. A lot of theoretical work and engineering went into understanding implosion before a working bomb could be built.

The enriched uranium bomb, however, was considered to be such a sure thing that it wasn't even tested before it was used on Hiroshima.

If you look at the overall history of the Manhattan Project one thing stands out--the numerous unknowns forced the project leadership to hedge their bets by using multiple different techniques simultaneously. For example, plants to separate uranium using gaseous diffusion, thermal diffusion, and electromagnetic separation were all built on industrial scales. And an entirely separate infrastructure was built to produce plutonium and chemically separate it from the reaction byproducts.

[David Hess]

That was the plutonium implosion bomb. Implosion was required for the plutonium bomb because plutonium had too high a spontaneous fission rate to use the gun mechanism. A lot of theoretical work and engineering went into understanding implosion before a working bomb could be built.

The way I remember it from two difference sources is that pure Pu239 could have worked in a gun type design, but their plutonium had too much contaminating Pu240 leading to a high spontaneous fission rate.  The Pu240 is created from Pu239 absorbing a neutron during the production process so to avoid it, a lower concentration of Pu239 has to be accepted for chemical separation lowering throughput.  You can make a lot of Pu239 per batch and accept a higher concentration of Pu240, or make less Pu239 per batch and get a more favorable ratio.

Nuclear weapons intended for naval deployment, where they will be in unavoidable close proximity to personal, use a process that cycles the Pu239 out more often so less Pu240 is produced making the cores are less radioactive.

[dietert1]

Wikipedia describes Szilards early ideas as speculation. The science happened 1938 between Otto Hahn, Fritz Straßmann, Lise Meitner and Otto Frisch. Szilard reproduced the results of the german groups in 1939 and later joined the Manhatten project. In the end he opposed using the bomb for military purposes.
When travelling to visit Einstein in the USA Niels Bohr talked about the induced fission results to his former scholar Wheeler and to others. The concept of a controlled nuclear chain reaction is attributed to Enrico Fermi and 1942 they had the first reactor setup in Chicago.

Regards, Dieter

[Veteran68]

Well murdering your prof with cyanide is a pretty big personal error up there with random bombings. I am GUESSING that didn't really happen?

According to "Modern Prometheus" Oppenheimer did indeed inject some type of poison into his professor's apple, or at least he claimed that he did.  The exact details vary, depending on who is relating the story.  The professor probably didn't eat the apple.  His father pulled strings so that Oppenheimer wasn't expelled or prosecuted, but one of the conditions was that he take psychiatric counseling.  He was definitely a troubled, brilliant, young man.

[HuronKing]

Well murdering your prof with cyanide is a pretty big personal error up there with random bombings. I am GUESSING that didn't really happen?

According to "Modern Prometheus" Oppenheimer did indeed inject some type of poison into his professor's apple, or at least he claimed that he did.  The exact details vary, depending on who is relating the story.  The professor probably didn't eat the apple.  His father pulled strings so that Oppenheimer wasn't expelled or prosecuted, but one of the conditions was that he take psychiatric counseling.  He was definitely a troubled, brilliant, young man.

If *some* form of the incident never happened, I wonder why Oppenheimer's parents had to buy off the school to keep him from getting arrested.

It's unclear exactly what he did since according to witnesses Oppenheimer told different people different things... but it is evident he did a naughty whatever it was.

[KE5FX]

That's some impressive string-pulling.  "Uh, Dad, I tried to kill my professor with cyanide and now they're going to kick me out of school.  Bunch of reactionaries.  Can you, you know, say something to somebody?"

[TimFox]

His parents were wealthy.  Enough said.

Szilard and Fermi patented the nuclear pile in the US:  filed 1944 and granted 1955.
https://patents.google.com/patent/US2708656A/en

When I got to the University in 1970, the new library built on the site of Stagg Field had just opened.
The last bit of the stands (at 57th and Ellis) was supposed to be gone by then, but there had been a bookstore fire and they kept the run-down building temporarily until the bookstore could reopen.

[peter-h]

Implosion was required for the plutonium bomb because plutonium had too high a spontaneous fission rate to use the gun mechanism.

Curiously that isn't the case. David Hess is right.

You can make a "gun" device but you need a much higher velocity. The resulting device is about 5m long. The US built some mockups and spent a lot of time dropping them to get them to fall in a stable way instead of wobbling. I have a book by a guy who tracked down a lot of the drop sites of various mockup devices (he got the coordinates from a "contact"). Very good read.

Implosion is of course much more compact. As interesting is how they made 155mm shells... this is still well classified but most likely the PU was egg-shaped and charges convert it into a spherical shape. That destroys the shape of the shell of course but it doesn't matter by then.

[msuffidy]

It seems to me that you are working with a bomb material that is pretty much always putting out some neutrons, so you would not like to like just handle it. When you squish it together somehow, all of a sudden so many neutrons are splitting more and more nucleus until there is a lot of energy being created. So it was classified at the time, but like maybe if you had like a vacuum foam bubbles in a sphere and you could just smash it all into a small sphere that would do it. Ideally the geometry would be very regular between the explosives and the metal foam ball, so you don't want like a tube canister between them. Or maybe there could be like a neutron inhibitor that scoots somehow as it is crushed.

[David Hess]

It seems to me that you are working with a bomb material that is pretty much always putting out some neutrons, so you would not like to like just handle it.

The original plutonium samples which were tested came from a giant mass spectrometer used to separate the plutonium, so were pure Pu239 with a very low spontaneous fission rate.  The plutonium that came from the reactor later however had considerable Pu240 and the measured spontaneous fission rate was way too high to support the gun type weapon as designed.  That is when they knew they had a problem and seriously considered the implosion design.

The lower the spontaneous fission rate is, the more time is available to assemble a critical mass.  Real designs include some way to apply a burst of neutrons to the compressed core at the optimum time, and starting out with a higher number of free neutrons produces greater yield.

[Bud]

So many nuclear experts here, what are you guys doing on Electronics forum 

[David Hess]

So many nuclear experts here, what are you guys doing on Electronics forum 

Conversion weapon design is just a hobby.

[DonKu]

"The Day After Trinity" is the story of Oppenheimer and the development of the atomic bomb. The skeletons on sidewalks it shows are suitable for a "Terminator" movie.

https://en.wikipedia.org/wiki/The_Day_After_Trinity

https://duckduckgo.com/?q=%22day+after+trinity%22&t=h_&iax=videos&ia=videos

[coppice]

So many nuclear experts here, what are you guys doing on Electronics forum 

There are far more electronics engineers than physicists working on nuclear weapons.

[peter-h]

Seen the movie.

It's not bad although for non-informed viewers it suffers from difficulties in that there is basically no plot; it is just a long strings of events. It is a good attempt at historical accuracy.

The music is too loud in just a few short bits.

[Infraviolet]

"There are far more electronics engineers than physicists working on nuclear weapons."
And then one remembers that some of the most notable books on Electronics were actually written by Physicists.

[coppice]

"There are far more electronics engineers than physicists working on nuclear weapons."
And then one remembers that some of the most notable books on Electronics were actually written by Physicists.

Most of the really good RF engineers I have worked with had physics degrees, and were not eligible to join the relevant UK engineering institution (whose name has changed over time).

[peter-h]

I doubt anybody posting on this thread has any idea of the electronics in a modern atom bomb

And I am sure they have come a long way from a load of krytrons

were not eligible to join the relevant UK engineering institution

They must have felt absolutely terrible to be thus deprived of a real sense of belonging

[coppice]

were not eligible to join the relevant UK engineering institution

They must have felt absolutely terrible to be thus deprived of a real sense of belonging

I know very few electronics engineers who went through the process of becoming a full member of the IEE (its old name). A lot of us joined as student members and that was it. I only found out about the physics people being excluded when I showed minor interest in becoming a full member, and couldn't muster four people who were full members to act as sponsors in a business with hundreds of electronics engineers.

[MadTux]

Fun fact, you could simply build a nuclear weapon with natural uranium back 3.5billion years ago.
Unfortunately the good stuff decays much faster, so much less is present now 

[m98]

I doubt anybody posting on this thread has any idea of the electronics in a modern atom bomb

And I am sure they have come a long way from a load of krytrons

I don't think they would have moved away from Krytrons, or rather Sprytrons. Why would they? Semiconductors are still catching up to their performance for pulsed power switching. Diode laser igniters might be the next technology step, but again, why would they want to innovate something that was probably perfected half a century ago?

[MadTux]

I doubt anybody posting on this thread has any idea of the electronics in a modern atom bomb

And I am sure they have come a long way from a load of krytrons

I don't think they would have moved away from Krytrons, or rather Sprytrons. Why would they? Semiconductors are still catching up to their performance for pulsed power switching. Diode laser igniters might be the next technology step, but again, why would they want to innovate something that was probably perfected half a century ago?

Exactly, wouldn't go boom any different, decrease in size probably only marginal, while huge risk with reliability of designs tested 100s of times in the 1950-1960s...

[peter-h]

Regular tests are taking place these days too, but without the active material. So you can just do it in a bunker.

They must be using MOSFETs or similar nowadays. It is very easy. About 30 years ago I designed a handheld exploder device (these are widely used to trigger demolition/mining charges) and the spec is typically a few hunded volts and a few amps, discharged from a specific capacitor. There is a spec on the V/I profile to be achieved. The krytron or similar device does the job nicely (even at ~10000G for a 155mm shell - https://en.wikipedia.org/wiki/W48) and at the time there was nothing else because valve technology won't deliver high currents. The krytron works by flashing over. There is totally no reason to use them today.

[msuffidy]

"The Day After Trinity" is the story of Oppenheimer and the development of the atomic bomb. The skeletons on sidewalks it shows are suitable for a "Terminator" movie.

Is this it?
https://archive.org/details/thedayaftertrinity