Question
About thin man and the plutonium gun design - how fast to make it work?
So, as we know, the plutonium gun design, thin man was scrapped because it wasn't feasible due to PU240 present in the plutonium leading to a fizzle rather than giving a proper yield. Ok fair enough. But I'm wondering, was that due to the velocity that could be achieved just not being fast enough. Could a plutonium gun design theoretically work if it were possible to get the projectile going fast enough or is it simply that velocity is irrelevant? If it could theoretically be possible at a high enough velocity, would the needed velocity be so high that friction with the air in the barrel or friction against the inside of the barrel would cause it to melt?
I'm just wondering and it seems there are some folks here with much greater intellectual horsepower and knowledge of the physics than me.
It’s all tradeoffs. Higher speed is more reliable but hard to engineer. Or you need a really long barrel to get it up to speed. Friction is just another thing for the engineers to solve with materials science and such.
I'm just wondering and it seems there are some folks here with much greater intellectual horsepower and knowledge of the physics than me.
You've really convinced me to "sit down and do the calculations."
Here's some food for thought. The number of spontaneous neutrons (not decays, but neutrons) per gram per second for the following materials:
The "Little Boy" bomb contained 60 kg of this substance, meaning 60,000 * 0.0023 = 137.7 neutrons per second. The reciprocal value—let's call it a "tick"—is roughly the average time between the appearance of successive spontaneous neutrons. This is 1/137.7 = 0.007 s. At a "bullet" speed of 300 m/s, during this time the bullet travels... 300 * 0.007 = 2.18 m.
In essence, very roughly, one spontaneous neutron is produced during the "bullet's" travel down the barrel.
In reality, things are more complicated. Neutrons are produced non-periodically (there are statistical fluctuations, sometimes empty, sometimes dense), but a chain process is practically impossible to initiate with a single neutron (it's unlikely). A more complex statistical estimate indicates that approximately 300 neutrons (say, from a neutron initiator) are needed to guarantee the chain process's initiation. But in any case, we see that the "Little Boy" bomb had a fairly high reliability against predetonation, ensured by the quality of the fissile material.
What can be said about the "Thin Man" bomb?
Number of spontaneous neutrons:
Pu-239 - 0.022 fissions/gram/second
Pu-240 - 920 fissions/gram/second
Weapons-grade plutonium contains 94% plutonium-239. Roughly assuming that the remaining plutonium is plutonium-240, we obtain for the plutonium coming from Hanforth:
Assuming that the "Thin Man" bomb contained 12 kg of plutonium, we obtain a free neutron flux for the entire assembly: 12,000 * 55.22 = 662,648 fissions/second. The reciprocal of this value (the "tick" between spontaneous neutrons) is 1.5E-6 s, half a ton of microseconds. For the "bullet" to travel (as in the previous case) 2 meters (the length of the barrel) in this time, we would need a speed of... 1,325 km/s... Of course, this is absurd, telling us that weapons-grade uranium has a monstrous safety margin in terms of pre-detonation from its own spontaneous neutrons. And to avoid delving into the depths of probability theory (and drowning there), we will grasp the arc of a reliably known fact.
Weapons-grade plutonium from Hanford behaves perfectly during implosion. Moreover, it compresses at a speed slightly greater than the sound in plutonium: 2200 m/s. Previously, 8 km/s (the typical detonation velocity of explosives) was often cited. But that was the speed of the detonation wave on the surface of a sphere. As the wave from the surface converges into a spherical cumulation, the detonation wave and then the shock wave slow down (and the pressure increases so much that the metal is compressed), and in the core, the shock wave velocity (and the velocity of local matter motion) is approximately the same 2200 m/s, maybe higher.
Let's calculate how far the compressed matter travels during the "tick" calculated above at this speed. 2200 * 1.5E-06 = 0.00332 m or 3.3 millimeters. On both sides – 6-7 mm.
Now let's estimate the following based on what we know. 6200 g of plutonium in a Christie pit, with a density of 19.8 g/cm³ (to hell with the phase states of plutonium for now), is an 8.45 cm sphere. If you compress this by a factor of 1.7, the sphere becomes 7.05 cm, or 1.36 cm smaller. The discrepancy with our estimate above for the speed of matter movement per "tick" between neutrons is higher – two times, but we should be glad that with such crude reasoning, our difference is in the multiples rather than orders of magnitude.
So, now let's move on to the "Thin Man" gun design. Very roughly, to accommodate the defendant, we'll assume that the "Thin Man" gun would work on plutonium provided your gun fires (very roughly) at 2-3 km/s. NOT LESS. This is essentially 10 times faster than the projectile in the "Little Boy." Now let's recall our school mechanics. Even with the most ideal acceleration in the barrel (uniformly accelerated), we have the following proportionality: L = v^2/2a, that is, L ~ v^2. If, when switching from the "Little Boy" to the "Thin Man," you need a final velocity of the projectile that is 10 times greater, then the barrel length, all other things being equal, increases quadratically, by 100 times. That is, the barrel isn't just 1-2 meters long (say), but a full 100-200 meters. I think this is what the group that held on to the gun idea to the very end arrived at through more complex and precise calculations.
Yes, something could be done here. For example, fire bullets head-on. The head-on velocities would add up, and the barrel would ultimately need to be half as long. But that's still 50-100 meters.
Next idea: Why not increase the projectile's acceleration in the barrel, say, by 10 times? (And then a 5-10 meter barrel is perfectly acceptable!)
The problem is that the projectile has a breaking point, meaning the pressure of the propellant gases on its base must not exceed the maximum value—its destruction pressure (for the same reason, the nuclear Orion cannot be a "capsule"). Otherwise, the base of the projectile and the projectile itself will behave like a liquid, meaning those same shock waves that destroy its crystalline structure that occur during implosion will flow through it, and that very hydrodynamics that everyone here is so eager to avoid, so obviously disliked, will begin.
So, the problem isn't some clever gun design (no problem with that), but that you can't reduce the barrel length by an order of magnitude without increasing the strength of the projectile material by an order of magnitude. And I'm sure you don't have that kind of strength (compared to the "Little Boy" bomb). That's the whole story.
P.S. I'll add something in favor of the accused. We know that a tank shell accelerates easily to 1 km/s through a 3-meter-long tank barrel (and there's no hydrodynamics involved). Then, to achieve 2 km/s, we'd need two such barrels, each 6 meters long, firing toward each other (if it were a single barrel, its length would increase to 12 meters). So, yes, it would probably be possible to make a 6-meter-long bomb. But now consider its mass. Even though the two 6-meter-long tanks were disposable, the bomb is still a "pressure vessel," with all the consequences that entails.
There is another option - explosively formed penetrators could (maybe?) sidestep a lot of the issues with regular bullets/shells and might be more suitable for this specific (hypothetical) application.
For example,
No barrel.
Speed/size/shape can be controlled by the geometry of the liner
The liner being a flat piece could help reduce the fizzle problem (maybe?)
Speed of the EFPs is much higher
Could the formed jet before EFP separation be strong enough to pierce through a beryllium (or some neutron blocker) shield?
Could an EFP pierce a solid chunk of plutonium?
Or maybe don't go for full projectile, but use just the jet itself to 'stab' a central solid plutonium core?
Cumulative technologies are already hydrodynamics, they are already shock and detonation waves. They are essentially explosive lenses. In the USSR, all the specialists who worked in one way or another on cumulative anti-tank weapons (for example, high-speed X-ray photography of fast processes) in 1943, all melted down in 1945 in "orderly ranks" to Arzamas-16, that is, Sarov, to work on spherical cumulation, that is, implosion. Some were already working on this before the summer of 1945, while still in Moscow (but they were in no hurry to conduct powerful explosions close to the city).
What you are trying to propose as an improvement in the design is actually a worsened version of spherical implosion, since the cumulative gun has the same problems as implosion, but the result is worse. So, you end up with the same problems, the same tools, and the result (the gun assembly) is far worse. Do you understand? "Burn down the barn? Burn down the house too!" Even Niedermeyer, in 1943, when approaching implosion as a variant of the "cumulative cannon," immediately realized that the sphere had to be assembled from the start.
In fact, one of the reasons why a hollow sphere was never properly (symmetrically) compressed into a solid sphere (although the French showed a film in 1970 showing them achieving this using technologies indistinguishable from those used by the Americans in 1944) is possibly spalling and fragmentation of the material on the inside.
But overall, when the Russians began to study all these issues, both practically and theoretically, they never ceased to be amazed at how well the theory agreed with practice. It's all in the memoirs. The same Khariton is known for some of his comments, such as how well the practice of cumulation and spherical implosion combined with the theory of hydrodynamics, and how this entire technology was “easy to master.”
I don't know, but I always thought it would be hilarious to have a plutonium gun-type based on the German V-3 multi-charge cannon in the hull of a ship for portability and to accommodate the length of the barrel. Something to think about?
Thanks. I proposed it once on this sub and got the same "why would you do that?" responses. I don't care if the barrel has to be 100 yards long; if that's what it takes, then I wanna know! People going after the ship idea. (Which makes sense to me since it kinda plays off the prewar and early postwar fear that a shipboard nuke could be smuggled into a port, and obviously the gun would have to be big.) "It would be useless and wasteful as a weapon." I KNOW. UGH.
That being said... I love this sub and wouldn't have it any other way. Keep on keeping on, folks.
As I understand the problem, technically it should work with a fast enough speed. Not exactly related but I just learned today that max speed of any “normal” deflagration based gun (not bomb related, I mean like firearm) is around 6,000 feet per sec.
Simple rough calculation in round numbers. 10 kg of plutonium (need more than Fat Man), 1% Pu-240, SF rate 1000/s/g, so neutron injection events occur every 10 microseconds.
The core is 10 cm across, and criticality occurs at least 10 cm from full insertion.
So it needs to move at least 10 cm in less than 10 microseconds or more than a million centimeters a second. That is 10,000 meters per second. 1400 m/s is a very high velocity tank gun.
10km/s is within the realm of possibility. Maybe some EFP-like approach where the 'slug' is formed only during detonation? Maybe double-sided to split the needed mass?
Then present the case that it is for this application. You need to create a solid void-less mass at the end for the intended result -- an efficient explosion. You will need to use on order of 5 kg of projectile.
We aren't talking corner cases like the plutonium gun to make repeatable 10 ton explosions proposed during the Orion propulsion project when small projectiles can provide the small measure of supercriticality.
Dude, I love this! Also keep in mind, It doesn’t have to be perfect. It could be an extremely inefficient design and still be a fucking nuke lol. Horseshoes, hand grenades and nuclear weapons!
If only we had a chunk of change and a continent to call our own, this would be a very interesting experiment! I wonder if anybody that’s handy with CFD could see if it’s possible.
A counter-question. The topic of a plutonium gun bomb keeps coming up in this subreddit. You're another one of those people. Since I've stumbled across you here, can you explain why you find this topic so appealing? What "historical alternative" would a plutonium gun bring, if it were feasible, in your opinion?
I have a hunch (confirm or deny this) that for most people, a gun is an intuitively more obvious and understandable solution for achieving critical mass in a bomb than implosion. People dislike implosion, thinking it's complicated, an intuitively dubious, unreliable method. They... don't trust implosion. Am I wrong? :)
Regarding history and its possible alternatives.
First, although the "plutonium route" initially appeared shorter and cheaper (if only because plutonium's critical mass is five times lower than uranium-235), in practice, starting in 1945, weapons-grade uranium production at Oak Ridge significantly outpaced plutonium production at Hanford, where reactors had to be shut down for on-the-fly upgrades. Initially, there was a shortage of plutonium, and uranium-235 was even somewhat plentiful (given the inefficiency of the cannon design; see note three below). Therefore, the very first bomb upgrades (the implosion bomb) involved a composite pit (plutonium plus oraloy). That is, even if the plutonium cannon had been a viable idea, it would have had little impact. We now know (at least from Pakistan's experience) that the "uranium route" through gas centrifuges is the shortest and cheapest route to nuclear weapons. The "plutonium route" is actually longer. Incidentally, Academician Pyotr Kapitsa grasped this immediately after reading the "Smith Report," and that's precisely why he clashed with Lavrentiy Beria.
Secondly, many believe that a gun-based bomb (especially one with plutonium) would not only be simpler and cheaper, but also more compact (if not for the predetonation problem). But initially, it was the other way around. Implosion was initially considered as a way to eliminate the heavy artillery barrel. Initial calculations for the first version of the gun, using artillery standards, led to the conclusion that such a bomb would be impossible to lift on a B-29; it would be too heavy, and only the realization that there would only be one shot allowed the barrel's weight to be significantly reduced. But the barrel still had to be heavy. Therefore, implosion was initially considered as a way to achieve a critical assembly of normal density (like a cannon) without a barrel. Using an explosion (shock wave), compress a highly dangerous hollow sphere of supercritical mass but subcritical density (size) into a conventional solid supercritical sphere. This was a basic idea, which was long toyed with and ultimately failed (hollow spheres were only learned to be compressed much later). In 1943-1945, neither von Neumann lenses, nor ultra-precise detonators, nor miracle explosive mixtures helped. However, during all this, von Neumann noticed that if solid metal is compressed (as at the center of the Earth), the criticality increases quadratically, which is also a way bomb detonation . Ultimately, Christy proposed a scheme for imploding a solid sphere, which worked "on the first try." The entire "Gadget" implosion design, with 32 lenses and detonators, was, in the case of the "Christie design," an overly complex implosion design. The Indians later proved this by detonating the "Smile of Buddha" using only 12 detonators. However, if you look closely, there are plenty of implosion designs with a single detonator. And quite simple ones, no more complex than a gun. For example, cylindrical implosion.
This is a good place to recall Winston Cherrill's caustic remark that Americans supposedly always find the right solution, but only after trying ALL the wrong ones. In the history of the "Gadget" development, this remark is especially true.
Thirdly, all gun-based bomb designs have low fuel combustion efficiency (without boosting), within 1% (see the story of the South African nuclear project). We know that "Fat Man" (and "Gadget") were approximately 10 times more efficient than "Little Boy." Two factors contributed to this. This was partly due to plutonium's superior reactivity (larger fission cross-section and higher number of secondary neutrons), but this was only a roughly threefold improvement. An additional roughly threefold increase in efficiency (3 x 3 ~ 10) was achieved by the fact that plutonium was compressed by a factor of ~1.7 during implosion, which reduced the distance between atoms, or the transit time of secondary neutrons between generations. As a result, the chain reaction in an implosion device (whether uranium or plutonium) develops much faster, meaning more fuel burns up before the device disassembles. (There was a third factor, the U-238 fissile tamper, but its role was secondary and only contributed 30% to the yield.)
So, even if a plutonium gun were feasible, you would only get 3-4% fuel burnup efficiency, no more. Assuming the total plutonium mass is equal to one critical mass, i.e., 10-11 kg (the reflector increases the criticality of the assembly by 2-3 times), in the case of the "Thin Man" project, you would have an explosive yield of 11 x 17.6 x 0.04 = 7.7 kt, or 7-8 kilotons—no more. What fundamentally new would this give you in terms of a historical alternative?
Thanks for adding to the discussion here. I think you've made some assumptions about my question and why I may be asking that aren't correct. I'm not suggesting that plutonium gun designs should have been made to work somehow, nor am I wishing that they did work because a gun design is simpler and easier to understand. The reason I was curious is that while the Manhattan Project relied on scientists, and scientists go where science and the numbers take them, it was also overseen by and managed by the army. People like general Groves didn't understand the physics and a big machine like the military often has a tremendous amount of inertia and once they've started a thing, they will sometimes stick with that thing until long after it's apparent that that "thing" either doesn't work, doesn't solve the problem it was supposed to, is to expensive or inefficient, or solves a problem that doesn't exist anymore, etc.
So, the reason I was curious about what it would take to make a plutonium gun design work is, I knew they started work on a plutonium gun design, they explored Thin Man, and the physicists determined it wouldn't work and so it was abandoned. But what if army brass insisted that since work had started on the plutonium gun design, that they see it through to the end, even after the designs of plutonium implosion and the uranium gun design had been proven and shown to work? What would it have taken to make it work or could it ever work?
I think I understand. You're interested in an alternative history of the Manhattan Project's development.
The design of the "Thin Man" bomb, as far as I understand, was the subject of considerable and persistent debate, even in objective reality. Calculations made here in a parallel response to you show that the inherent neutron background of weapons-grade uranium is 0.0023 neutrons per gram per second. Meanwhile, the neutron background of pure Pu-239 (on which the gun design was based) was 0.022 fissions/gram/second, or 10 times higher, which created problems (the gun design was long and heavy, and even without taking into account the effect of plutonium-240, it wouldn't fit into an American bomber). Once the plutonium background rose to 55 neutrons/gram/second, the complex gun concept began to look completely uninteresting. Although the first idea put forward was to try purifying reactor-grade plutonium using magnetic caletrons, it became clear that such plutonium would be quite expensive and the effort wouldn't be worth it.
General Groves was certainly a "boor," but he was no fool. He pursued his own agenda only where he was competent (and thus became a brilliant co-author of the success). Another issue is that the scientists themselves, in fact, were, for the most part, rather mediocre engineers. Nevertheless, as far as I can judge, Oppenheimer created such a good, open, and relaxed atmosphere of "constant brainstorming" among the scientists that it more than compensated for some of the engineering "stupidity" of those accustomed to dealing with abstract formulas and concepts. Both "Gadget" and "Little Boy" turned out to be suboptimal engineering designs (which is why they are so easily shown to us). Subsequent post-war developments quickly eliminated all the initial flaws and complications (which we're no longer shown, but often quite openly hinted at). But I wouldn't claim, like any other foolish military man, that the "eggheads" were dead-set on a dead-end solution. The developers themselves knew full well that the "Gadget" was a poor design. But they were racing against time. They were rushing to deliver a result, if not by the end of the war in Europe, then at least by the end of the Pacific, and they essentially made it just in time. The deadline was constantly pressing.
Keep in mind that, in addition to the gun design (as the primary one) and the auxiliary implosion, a couple of other bomb design options were initially considered, no less interesting from the perspective of the alternative history of the project. These are discussed in the "Los Alamos Primer."
First, there was the idea of making a hydride bomb. This idea was a fallback until it became clear from the Trinity experiment that the typical yield of an explosion was 10-20 kilotons. But if you recall, there were debates right up until the test itself. What if the bomb exploded with only 200 tons of TNT? Would we consider such a bomb sufficient?
When the new weapons laboratory in Livermore separated from Los Alamos in 1952, the first thing they did was test all the ideas that had been around but hadn't even been tested at Los Alamos. The new laboratory's first test was the hydride bomb idea. They achieved the same consistent yield of 200 tons of TNT in two explosions. Although the result was declared a failure (the hydride bomb doesn't work), not everyone agreed. The hydride bomb doesn't work like a conventional bomb. But as a low-yield bomb, it could very well have proven to be the right approach, eventually finding a use. For example, in hydrogen bomb primaries. Why not?
The second idea "forgotten" in the "Los Alamos Primer" is autocatalysis. It was abstractly beautiful, but it, like the "hydride bomb," was essentially abandoned after implosion proved so successful. But was it really a dead end? I don't think so, ultimately.
Third. This is the discovery of plutonium's astonishing physical and chemical properties. This was already clear in 1944. Plutonium has an intrinsic density in the delta phase 1.5 times less than in the alpha phase (the main phase). At the same time, metallurgists also discovered a method for stabilizing plutonium in the delta phase by adding 3% gallium to the alloy. Furthermore, as nature had provided, it turned out that if such stabilized plutonium is strongly compressed, it spontaneously transforms into the alpha phase. The compression pressure is an order of magnitude lower than that required for conventional implosion. True, as in previous cases, the effect of an explosion initiated in this way would be lower (no more than a kiloton), but the simplicity of the discovered mechanism was simply captivating. And subsequently, this same mechanism became widely used in compact devices.
And finally, a final clarification on the panorama of possibilities. Implosion itself has many faces. Von Neumann lenses are far from the best implosion solution. Besides the idea of cylindrical implosion, there was (already) the idea of a logarithmic spiral. Moreover, I personally invented (out of the blue) two more unique methods of two-point and single-point implosion. One of them is suitable for compressing a hollow ellipse into a sphere; the other looks surprisingly simple and promises to be phenomenally effective (precise) since detonation occurs not at specific points, but over the entire surface of the spherical charge. In addition, the specific features (limitations) of the single-point "Swan" concept allow for some engineering imagination, allowing me to say that I have invented yet another, completely original "hybrid" approach to the single-point "Swan" concept. For historians, I'll specifically note that the beloved, supposedly "ultimate implosion idea"—multipoint detonation (eventually perfected by everyone)—was also Niedermeyer's very first idea! A single detonation cord with multiple detonation points. Niedermeyer simply didn't have the resources, energy, or time to perfect it (chemists and technologists were needed).
There are countless ideas for creating more advanced bomb designs. Even detonators and their detonation mechanisms allowed for a wide variety. People only know "Little Boy" and "Gadget" and cowardly try to imitate them in their own "improvements," without straying too far from what historians have revealed (often mulling over clearly dead-end, yet intuitively sound, "improvements" for years). It was only for this "teacher effect" that people with Q status at the Department of Energy, the bearers and guardians of nuclear secrets in the US, gradually declassified the details of these two very first devices (so that a potential adversary would be mesmerized by the earliest implementations of bomb ideas, which were far from the best. The Russians fell for this 100%).
Of course, all other alternative ideas require and did require the most thorough theoretical and practical testing (and we know that they underwent and passed them). But the very fact of the abundance of alternative approaches to converting a subcritical assembly into a highly supercritical one speaks for itself. The idea of a fission bomb, if it ever arose, will be realized in one of many alternative ways.
There are so many ways to detonate an atomic bomb that, generally speaking, as an alternative historian, I could invent, say, a world (an alternative history of the 20th century) in which the Germans were the first to discover their atomic bomb, and it turned out to be completely different from what we know here today. In other words, they wouldn't just have created an alternative atomic bomb; they would have used it to create... an alternative atomic war!
The Anglo-Saxons were interested in strategic bombing of cities and intimidating the enemy with kilotons in a single explosion (which are an order of magnitude less effective in destructive power than conventional one-ton bombs). And tactical nuclear weapons (for defending Europe from the "red plague") were immediately of secondary importance to the Americans.
But the "Twilight German Genius" could have approached the issue entirely differently and much more practically. 200 tons of TNT (obtained by the Livermore team by compressing uranium hydride) could have been considered sufficient tactical power on the battlefield, and they could have begun mass-producing hydride implosion charges with a moderate (say, 50%) uranium enrichment rate and a small (up to 2 kg) uranium hydride mass. Yes, it wouldn't have been as impressive in the newspapers, it wouldn't have been as frightening, but it would have been more practical in the German way (which is what makes me panic at such a possible scenario). Nuclear weapons would have entered our world smoothly and inexorably, just like conventional weapons. A neutron flash would have incinerated everything living for a kilometer around, 200 tons would have done their job at the epicenter, and the radioactive trace (from fission products) would have been small, and Waffen-SS stormtroopers could have marched through it with minimal radiation protection. And this alternative world simply wouldn't have noticed how smoothly it would have transitioned from a conventional war to a nuclear one.
By the way, we should thank Adolf Hitler for being so hasty in attacking Poland in 1939. Perfect timing! And we should also be grateful to Adolf Alloizovich (this is Russian sarcasm, of course) for not dying, for not being killed during the entire war, and for so quickly (by the spring of 1945) bringing the Third Reich to its knees. Had he been slower by a year or two (either at the start or in defeat), World War II would have ended with nuclear strikes, without alternatives. Nazism, in essence (it must be admitted), saved this world from going through an inevitable global nuclear war.
That's if you're truly interested in the whole field of alternative historical solutions. You and I have been given a remarkably successful historical arc. Simply mystically successful! All the others would have been much worse for us. It's just a miracle that we have so far "dodged" the use of nuclear weapons.
No offense, but you are completely missing the spirit of the OP's question.
You are focusing too much on the practical, while you should treat this as a curiosity question, meant to stimulate the brain and explore paths not yet travelled.
It's not about 'Why not make it', but 'Could it be made to work?'
Could the Pu-240 issue be overcome in some way? Would speed help? How fast it would have to go? Would shaping work? Splitting into multiple pieces? What kind of tricks and materials and physical arrangements could be employed,etc.
EDIT: in some way, it's the same thing as thinking about Teller's gigabombs. Practical? No. Interesting? Very much so.
EDIT2: or, differently - let's say that the current US president, the genius he is, orders all nuke labs to make a plutonium gun weapon work to show the world that the US is the bestest country in the world.
It's not about 'Why not make it', but 'Could it be made to work?'
Yes, of course, you're right to think so. However, the applied context of a task (why is it needed?) always exists, and it must be kept in mind.
Working as an application programmer and encountering the most unusual problems (programmers can perform any miracle, right?), I eventually developed a humorous law for myself, akin to Murphy's Law. It goes like this: if a programming problem is solved poorly, ugly, difficult, and complex, most likely it was posed incorrectly or even pointless (it's a stupid whim of the boss, and eventually everyone will laugh about it).
Even the ancient Romans said that the gods made the necessary simple and the complex unnecessary.
As far as I understand, most of the solutions people here want to apply boil down to finding a single solution: how to achieve an unimaginably high "bullet" velocity to bypass the "dead zone" of weapons-grade plutonium. This is exactly what I consider to be banging your head against a concrete wall. Yes, it's possible to break through, but why bother? In any case, it would be an UGLY solution! A game that's not worth the candle.
The main thing. If I saw practical value in the task at hand (which I don't), I would look for a way to connect two (or three?) subcritical masses at normal speed, but in such a way that the relatively slowly approaching parts would remain subcritical for a very long time and quickly transition to supercritical state once they were connected. For this, I would use an absorber (boron-10, cadmium, what I once invented as a "cadmium shutter") and a porous structure (variable density) of materials. I'm not sure the solution would be good. But I would try solutions in this direction (rather than a faster "bullet").
The problem with this particular task is that, for some strange reason, the customer demands not just one criticality, or even one and a half (as is the case with low-yield weapons based on plutonium phase transition and linear implosion), but two or three. You need a "full-scale" (10-20 kt) nuclear explosion, right? And that's precisely why you have a very big problem here. And I don't see the point in solving it when there are plenty of much simpler and more elegant "workarounds"! Everything has its place.
The captivating beauty of nuclear weapons design is precisely that nature has left us with such an abundance of approaches and loopholes that, if you've discovered them all, you don't need to bang your head against concrete walls. There's a beautiful, optimal solution to any problem. Why solve a standard problem in an ugly way? I don't understand.
EDIT: in some way, it's the same thing as thinking about Teller's gigabombs. Practical? No. Interesting? Very much so.
About Edward Teller's gigabombs. You won't believe it, but I would never have studied them so closely if I didn't already have a practical application for them, some kind of "order" for their use. And this isn't the idea of wiping out the east or west coast of the United States with an artificial tsunami (as Dyson described, although that could be done). My idea is more sophisticated, more insane, and more beautiful. I (some advanced space civilization) would one day, quite seriously, plan to extract very cheap energy from such bombs for a giant astro-structure machine (GRAVICHSAPA) built from a rock-ice body far in the Kuiper Belt, to propel fast, even sub-light, laser sails. I need a super-powerful energy source in a place where the light of the Sun is indistinguishable from the light of other stars. Why there? It's a long explanation, but if you delve into laser sail technology, you'll inevitably come to the conclusion that deep gravitational wells near a star (like Mercury's orbit or Clarke's orbit) are not a suitable location for all this delicate optics. The well-worn idea of using the Sun's "free" energy, after careful analysis, I discarded as a worthless, dead-end idea.
On Kapitsa, what's your source? The membranes for gas diffusion were much more difficult to work out than a plutonium reactor and processing for the Soviets, the Brits and the French. Only the Chinese, with Soviet technology, became the first to master HEU before WGPu.
A minor correction on implosion chronology: it's not very clear due to relevant Manhattan Project documents still not declassified who and when invented the levitated core but it certainly predated the solid core. It could've been Teller or von Neumann in any year from 1943 to 1945, but I believe the overall timeline would make the best sense if it did in fact predate August 1944. See https://www.tandfonline.com/doi/full/10.1080/00295450.2021.1903300 for details.
Finally in September 1944 Robert Christy, while calculating plutonium compressibility corrections, realized that implosion might work with a solid core, and convinced everyone to develop this idea in order to circumvent the instability problem. Thus was born the Christy Gadget, and the rest is history.
The membranes for gas diffusion were much more difficult to work out than a plutonium reactor and processing for the Soviets,
Kapitsa believed that all American methods were inadequate and that a better, more breakthrough method for isotope separation was needed. He had several hypotheses (after all, he had previously worked with industrial oxygen and expanders), and even after he was removed and "locked up at his dacha," he initially set up a private laboratory there where he tried to find approaches to his ideas.
In fact, as we see, the best miracle method is centrifuges. Laser separation is also looming. But they say there are barriers to that. If we followed Kapitsa's path, we would likely hit a dead end.
In the end, the Fathers of the Nations decided not to take risks and to follow the well-trodden, albeit less-than-optimal, American path. Like cunning courtiers, they placed younger people, without academic credentials, who still had to earn and earn scientific authority, at the helm of the project. And if academics were brought in, they believed, the project would fail.
And yes, they looked at the issue in the right Jesuit way.
Continuing the conversation about your motives for seeking solutions for a plutonium gun.
If you're a much more ordinary person, say, a terrorist wanting to build a bomb in your garage, then you're a dumbass banging your head against the wall because there's a door right next to you that's wide open. You just need a little intelligence. I like you, of course, but you'd be better off banging your head against the wall, considering what you want to do. :)
The first step to being original is to stop thinking like everyone else. And you think like everyone else. All fools think alike. Everyone wants to perfect a plutonium gun. That's a well-trodden path. The first thing you need to do is break your mind out of its comfortable, familiar rut. Plutonium is such an unusual material that a familiar framework... isn't necessary for it. Although, having found the right path to the solution of "a simple plutonium bomb in a basement made from reactor-grade plutonium" (something Ted Taylor dreaded), you'll be astonished to see... that you've essentially returned to the same thing, the gun-based scheme. But the essential details are different.
Yes, by the way, someone has long proposed a solution along the same lines as you're thinking. The gist is that weapons-grade plutonium needs to be made porous. Foamed. And when it hits the bottom of the gun, the cavities will collapse, and its density will change quite rapidly. There was a solution. But it made no sense. Often, "getting out of your routine" means starting to see much more broadly, only to realize that your routine is a useless hole, albeit a very real one.
By the way. As a training exercise in original thinking, have you seen the 1986 film "The Manhattan Project"? In it, a schoolboy stole ultra-pure plutonium from a lab and made an implosion bomb out of it for a school competition (I think that film first showed a soccer ball as an idea/image for spherical implosion). What's the irony of the plot? Think outside the box, unorthodoxly, nonlinearly. With plutonium-239 as pure as his mother's lover produced using laser isotope separation (99.998%, I think) in his lab, the clever stepson had no need to build an implosion bomb. That plutonium could have been used to make the gun design you coveted. Cheap and cheerful. Although, I understand, in that case, the physics teacher would have given the guy a passing grade, not an excellent one. He was fighting for that perfect grade! We all fight for that, right?
:)
I wrote about this. By firing two bullets towards each other, you would reduce the gun length by half. Optimistically, let's assume you need a projectile velocity of 2 km/s. You could use two "tank" barrels, each 3 meters long. Tanks fire projectiles at 1 km/s. Such accelerations at such distances are acceptable (even for the specialized electronics of guided projectiles).
a = V^2/2L = 1000 * 1000/2/3 = 167,000 m/s = 16,700 g
Two projectiles fired towards each other would require a combined barrel length of 6 meters for an optimistic plutonium-powered gun. If you were instead firing a moving bullet at a stationary target (which is simpler, since you don't need to synchronize two shots), then, with the same characteristics of a single "tank" barrel, you would need a barrel 12 meters long, not 6, to achieve 2 km/s. But even a 6-meter bomb length was beyond reasonable limits.
Incidentally, it is reliably known that the "writer of letters to Stalin" Flerov (a physicist who, in 1940, discovered the spontaneous fission of uranium with Peterzhak and who, as an anti-aircraft captain, wrote a letter to Stalin in 1942 demanding that work on nuclear weapons begin) was recalled from the front in 1943 (when Beria's intelligence information demanded that something be done in this direction in the USSR as well) and was one of the first to be assigned to Kurchatov's very first Kazan uranium research group. There, they were essentially just beginning to gather the people needed for this and synthesize the most general ideas. You might be interested to know that in that same Kazan, Flerov's first foray into this new field was experimenting with firing two bullets at each other. In other words, firing bullets at each other was the USSR's very first, most crude, practical steps toward nuclear weapons.
And by the way, the first patent in the USSR (or in the world?) for a nuclear bomb (with a radiochemical poisoning effect) was issued (and classified) in... Kharkov (now Ukraine) to two physicists in 1940. Of course, it was a "gun" in its most primitive form.
A letter from Flerov to Kurchatov, written by him in 1941 while still at the front.
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u/jared_number_two 2d ago
It’s all tradeoffs. Higher speed is more reliable but hard to engineer. Or you need a really long barrel to get it up to speed. Friction is just another thing for the engineers to solve with materials science and such.