Yeah, once you get too big your blast sphere is basically in space and so that part does effectively nothing extra and your total damage per mass of fissile material drops even faster as you try to keep scaling. And even if that wasn't a problem, really big nukes are harder to launch/deliver and would be a much larger material loss if it was shot down prematurely. Having multiple warheads in place of one super large bomb is just a far more reliable attack plan.

They scaled it down so the plane dropping the bomb could escape.

And to reduce the fallout.

50mt vs 100mt came down to whether the jacket was U-238 or something inert. (U-238 can't do a chain reaction, but when subject to the neutron flux of an h-bomb it's willing to fission and increase the yield.)

One interesting thing about the Teller-Ulam design is that you can scale the bomb as big as you want. Imagine a skyscrapper sized bomb.

Edward Teller (who else) got there first with his Sundial design for a 10Gt bomb...

> If you really want to cause huge widespread destruction you are better off using multiple smaller megaton bombs. Still, it would probably ruin your day.

Isn't this the basic idea of ICBMs / MIRVs with multiple warheads? Basically nuclear cluster bombs.

I think that's just a side benefit to the MIRVs' main purpose of being more difficult to stop

I think they very much had to watch the weather for radiation dispersal with the large upwards column. Also why they scaled down the size I believe. Would need to validate this though.

Didn't Russia just create some kind of underwater nuclear torpedo to cause tsunamis? I guess they are fans of Dynson

With limited knowledge (the What If link posted earlier), would a tsunami created by a nuke be more damaging than a direct nuke itself? You'd lose the explosive and heat damage for the most part, and at least in my head the water would contain and dampen a lot of the explosion (although on the other hand water isn't nearly as compressible as air)

The scale of energy released is the problem. Tohoku earthquake (which caused the Fukushima tsunami) released ~600 million Little Boy's worth of energy. Yeah, modern bombs are bigger- you'd only need a few hundred thousand Tsar Bombas to get that much energy- but still we're talking an absolutely gargantuan amount of energy.

This is why no one looked at the idea until Putin needed something to threaten America with after GWB did a really stupid thing and pulled out of the ABM Treaty. And I don't believe that the official Russian sources claim it can make a tsunami, I think that's mostly propaganda.

Well, they can't exactly test that particular system without causing massive ecosystem damage. As for your first comment - you are commenting from a politically motivated position, not a technical one. Said another way, you are making the warfare 101, chapter 1, paragraph 1 mistake.

The 2011 Tohoku earthquake that created the devastating tsunami was an energy release of something like 600 million Hiroshima bombs. Nuclear weapons are just the wrong order of magnitude to make a tsunami, this isn't about politics, it's about scale.

> warfare 101, chapter 1, paragraph 1 mistake.

"All warfare is based on deception" - Sun Tzu

What every nation, Russia included, talks about and shows off has very little in common with what they can actually do.

In Russia's case we mere civilians can just directly observe the difference a lot of the time, enough for me to be comfortable projecting the same assumption where only real military analysis could actually tell for sure. The claim that this weapon could cause a tsunami is within the set of things even civilians can disprove.

This option is not available to us civilians for more competent cases such as China or Iran.

Alright, let's talk physics! Presume that every thing I mention is actually caveated with "so far as unclassified understanding goes." Also, another caveat that I was an intern at a WMD non-proliferation group two decades ago, so my understanding was never perfect to begin with and time may be playing tricks on me.

So the Tsar Bomba was designed to be twice as large as it actually detonated. What the hell?

See, a thermonuclear bomb like this is (in the Teller-Ulam design) a three stage weapon: first, the primary (a regular atomic bomb, generally a sphere of plutonium that is imploded really fast) goes. The primary is a fission bomb, where a bunch of fissile material (Pu-239 or U-235- or technically U-233 but that's never been done at scale- Pu239 is easiest to isolate so its most common) is rapidly pushed together and generates a whole bunch of energy. This is what destroyed Hiroshima and Nagasaki, this is an "atomic bomb." This energy release comes from the chain reaction of atoms splitting: one U or Pu atom splits into a chain of daughter atoms and gives off a lot of energy- and extra neutrons which hit other atoms and cause them to split, setting off a chain reaction of energy release when enough U/Pu atoms are dense enough.

And then the energy from that release is directed into a bunch of fusionable material (probably lithium-deuteride) which causes those atoms to get so hot they start to fuse. And that fusion (like in the sun itself) gives off much more energy- as a rough estimate let's say something like 10x the amount of energy from the primary.

And then there is a third stage, the uranium tamper. You take some depleted uranium (U238- which is what is left behind when you pulled out all of the U235 from the natural uranium) and you direct the energy of the fusion into that. And that causes the U238 to do fission (which it won't do normally, unless you dump a whole lot of neutrons into it). This is, basically, doubling the amount of energy released. It's this uranium tamper- which is basically free, once you have an enrichment program up and running- which was replaced by lead in the Tsar Bomba test, so it only produced half the energy it could have.

As a note, fission turns out to be where most of the fallout is generated, and fusion doesn't generate a much fallout. The infamous "neutron bombs" of the 1970's and 1980's were a common name for basically, a thermonuclear bomb without that Uranium tamper (e.g. something like a Tsar Bomba but smaller) which produced very little fallout relative to its size. This worried some people, who thought that a conventional NATO-Warsaw Pact war might go nuclear if the West German government could be convinced to allow the use of such a bomb on their territory because it had less fallout. This also explains why the uranium tamper wasn't included on the Tsar Bomba test, because that would have produced absurd amounts of nuclear fallout.

Also as a general rule large bombs aren't very efficient, because you are destroying everything in a sphere volume: to double the radius of destruction you need to increase the energy by a factor of 8. Once Minuteman came along, and there were a thousand very accurate ICBM's available (and then Minuteman III which added MIRV's so quickly tripling that- and the Soviets responded with SS-11) it was more efficient use of the expensive fissile material to put more smaller warheads around, because the delivery systems were no longer the bottleneck.

My knowledge of neutron bombs was mainly popular science saying it would "just" kill everyone in a radius without damaging anything else, but the way you describe it it's "just" a thermonuclear bomb without the third stage.

Neutron bombs are small fusion bombs designed for putting as much energy into the neutrons as possible. Set the bomb off high enough and the blast would not be worse than a big storm but deliver an instant-kill neutron dose.

Turns out to be a horrible idea, though--yes, that's what it does to it's target, but consider farther out. The quick kill dose is several times the kill dose--you likely have a bunch of enemy forces that are dead men walking. And when you put soldiers in hopeless positions they have a tendency to try to take the enemy with them. You just made a bunch of kamikazes.

So, in the Cold War, when NATO would do conventional war games, they almost always lost. (1) At some point or another NATO ran out of troops and a Soviet tank army Operational Maneuver Group broke through and there were no NATO forces left to stop them.

At that point it becomes a political question: will the NATO political leaders (most importantly West Germany) allow the use of nuclear weapons on their own territory, killing their own civilians? (2) Some people thought that 'neutron bombs' were destabilizing because they made it more likely that, under those circumstances, the West German government would say "yes, let's go nuclear" and then that would lead to an escalation chain and pretty quickly it's Dr. Strangelove. (That all depends on the idea that a conventional NATO-Warsaw Pact war was even possible, which I'm not sure is true.)

But that's why some people made it such a big deal, they thought that a bomb that had almost no fall-out might lead to nuclear weapons use, it's the political not engineering consequences of deployment that worried them. The engineering is not the constraint, in fact it's actually barely easier to build one.

1: Looking at the capabilities that the Soviet Army was supposed to have, not necessarily the capabilities that they actually had, the Soviet Army should have crushed NATO conventionally from anytime ~1950 on. As the Russian invasion of Ukraine reminds us, armies are not always actually at the level they claim to be.

2: The French- who were sort of in and sort of out of the NATO command structure- answer to this question was the Pluton missile which was not capable of reaching East Germany, could only hit targets in West Germany (from bases in France- it was a mobile missile that could theoretically drive into West Germany, but... come on now). So they had the ability to engage targets in West Germany, and there was no question of their political leaders: they were 100% totally willing to nuke Germany rather than let Soviet troops conquer their country.

According to https://en.m.wikipedia.org/wiki/Neutron_bomb; yes it’s basically a fusion bomb with a different casing but also can be tuned to put a good deal of that energy into very high energy radiation vs. thermal radiation.

What I don’t understand is how neutron activation can be avoided. In particle accelerators this happens to whatever is around the collision point, you end up with lots of radioactive sensors.