4 ms·

> The end of surface testing of nuclear weapons after the atmospheric test ban treaty effectively removed "cleanliness" as a significant concern for designers.

> The end of surface testing of nuclear weapons after the atmospheric test ban treaty effectively removed "cleanliness" as a significant concern for designers. Complaints about fall-out vanished, and so did the ability of the international community to monitor weapon design through fall-out analysis. The cost-effectiveness of lighter weapons put great pressure on designers to extract weight saving however they could, and it is likely that the idea of using non-fissile tampers disappeared very quickly. There is scant evidence that so-called "clean" designs were ever deployed in any quantity. I found this pretty interesting, if somewhat disconcerting. I always assumed that modern nuclear weapons were "cleaner" than older ones. Not sure if this was a misunderstanding on my side or a common misconception I adopted. If I understand this part correctly, the "cleaner" designs have significantly worse yield at higher weight, and are unlikely to be actually used today. Though I'm not entirely sure if this only compared relatively modern nuclear weapons and whether there are other aspects to this that affect how "clean" nuclear weapons are.

arethuza 5y ago
Cleaner designs tend to leave out the final fission stage in the standard fission-fusion-fission "H-bomb" design - as this is where most energy is generated even though fissioning uranium with neutrons from the fusion step is, I believe, inherently messy. Edit: I'd have thought the biggest factor in how messy things would be is whether it is a ground or air burst, rather than the weapon design.
- formerly_proven 5y ago
  Is radioactive fallout from a thermo-nuclear weapon an important consideration (compared to the destruction of the "thermo" part)? The bombs dropped in Japan only contained a few kg of fissile material, those cities were rebuilt within years. Modern bombs are probably way bigger, but even a W78 warhead comes in at only 120 kg or so and I'm guessing most of that is not plutonium. Compare this to the thousands of tons of radioactive or activated material that flew around Europe following the steam explosion at Chernobyl.
  - arethuza 5y ago
    According to Daniel Ellsberg the only thing considered by US planners was blast yield - fallout and direct radiation (particularly thermal effects) were ignored as their effects were regarded as too unpredictable. This was in the 1960s though - things may have changed. edit: Fall out, even with modern weapons, would be a huge consideration if you are downwind of a target likely to be hit by a surface burst. You can experiment on Nukemap with the different options: https://nuclearsecrecy.com/nukemap/ https://nuclearsecrecy.com/nukemap/
    - CapitalistCartr 5y ago
      It hadn't in the Eighties. If you want to be a nuclear war planner, I suggest Nukemap. https://nuclearsecrecy.com/nukemap/ https://nuclearsecrecy.com/nukemap/ No more plastic wheels to spin like a sliderule. Want to take out a target? What's your weapon system's CEP (Circle of Equal Probability)? How is the target built, that is, how much overpressure to destroy it, and how deeply buried is it? Now choose a weapon. If it'a high-priority target, aim more than one weapon at it.
  - caf 5y ago
    The fallout by mass isn't primarily the direct daughter products of the fission. It's the thousands of tonnes of pulverised dirt and rock (and concrete and steel and...) that has been neutron-activated and ejected high into the atmosphere.
    - refurb 5y ago
      This was my understanding as well. Radiation levels of daughter products from the weapon drop quite quickly. But the dirt that’s been neutron activated can take a while to come back down and the exposure levels are much higher.
- CapitalistCartr 5y ago
  Air versus ground is a major factor. In the early days, we targeted whole cities with air bursts, relying on a WWII mentality to warfare. Then, as we gained the ability to target specific military installations, which simultaneously became more hardened, we moved to high ground bursts, then impact bursts, which pretty much means a huge mess. We can easily dig a hole in the ground 60 meters deep, but that means a staggering amount of debris high in the air, some of which will be radioactive.
bouvin 5y ago
For a chilling look at how dirty things can be, I turn your attention to Cobalt Bombs: https://youtu.be/ANIc4NKj6WQ https://youtu.be/ANIc4NKj6WQ
EdwardDiego 5y ago
> Complaints about fall-out vanished, and so did the ability of the international community to monitor weapon design through fall-out analysis But then we get into seismic monitoring, SOSUS, and the infamous "double flash" / Vela Incident. And I totally believe it was the Israeli government testing their nuclear fission weapons with the help of apartheid South Africa. As both were regularly international pariahs, they had a lot of time for each other.
Symmetry 5y ago
In a war many thermonuclear weapons would be targeted at hardened military structures and so detonate close to the ground to maximize local pressure. In a scenario like that you'll get a large amount of fallout just from neutron activation of what was once the ground and the bomb casing won't expecially matter.
mandevil 5y ago
So, where does "dirty" in a nuclear bomb come from? The left behind remnants of fission getting mixed into dust and dirt, then lofted up into the air by the force of the explosion and coming down later downwind- that's fallout, which is the "dirt." Fusion leftover products are essentially fine, and if you explode your bomb high enough that it doesn't throw much dust and dirt into the air that also will limit your fallout (obviously burying deep under the ground also works, but that is generally impossible for a weapon, only matters for tests). One more thing to explain: a typical thermonuclear weapon is actually three stages: fission (the initial atomic bomb) which creates the high temperatures under which we can get fusion, which then gives off roughly an order of magnitude more of energy (second stage) which then hits a natural uranium tamper (third stage) which essentially doubles the amount of energy, at a cost of leaving a lot more fission left-overs around and making it much more dirty. (You can continue to stage indefinitely, but that makes the bomb bigger and less practicable.) The largest weapon ever tested, the so called Czar Bomba, actually had it's third stage uranium replaced with lead, so its energy came all (~97%) from fusion, therefore it had very few fission by-products and was very very clean. This sort of weapon with no third stage tamper is also known as a Neutron Bomb- the so called 'clean bomb' that kills people (with the radiation from the fusion) but mostly leaves buildings intact, and has minimal fallout. So why were neutron bombs scary? For most of the Cold War, when NATO ran exercises, they 'lost' within 2-9 days- where lost means that Soviet armored divisions started running free and unopposed. At which point it became a political question: can NATO use nuclear weapons to wipe away those divisions before they conquer everything? Will the German government allow NATO to use nuclear weapons on German soil- or will the rest of NATO overrule the German chancellors opposition?[1] A neutron bomb, which can kill everyone in a few kilometers with minimal fallout, might be a convincing argument in that situation, and that worried a lot of people about the potential for nuclear escalation. In the post-Cold War context, it is widely believed that the most plausible first use of an American nuclear weapon would be to take out a 'hard' target- one buried deep underground that the US National Command Authority decided needed to be taken out for some reason. That sort of weapon will be extremely dirty, because it will of necessity be right up against the ground, kicking up a lot of dirt and dust and so would have a lot of fallout. Additionally, if you are trying to maximize blast-per-weight or blast-per-dollar, getting rid of that natural uranium tamper is really hard to justify, just to be a bit cleaner to the people who are receiving this weapon. [1]: The first generation French SRBM, the Pluton, had a range of 17-120km, and was based in France- meaning it could only be used to nuke West Germany.

arethuza 5y ago

Cleaner designs tend to leave out the final fission stage in the standard fission-fusion-fission "H-bomb" design - as this is where most energy is generated even though fissioning uranium with neutrons from the fusion step is, I believe, inherently messy. Edit: I'd have thought the biggest factor in how messy things would be is whether it is a ground or air burst, rather than the weapon design.

formerly_proven 5y ago
Is radioactive fallout from a thermo-nuclear weapon an important consideration (compared to the destruction of the "thermo" part)? The bombs dropped in Japan only contained a few kg of fissile material, those cities were rebuilt within years. Modern bombs are probably way bigger, but even a W78 warhead comes in at only 120 kg or so and I'm guessing most of that is not plutonium. Compare this to the thousands of tons of radioactive or activated material that flew around Europe following the steam explosion at Chernobyl.
- arethuza 5y ago
  According to Daniel Ellsberg the only thing considered by US planners was blast yield - fallout and direct radiation (particularly thermal effects) were ignored as their effects were regarded as too unpredictable. This was in the 1960s though - things may have changed. edit: Fall out, even with modern weapons, would be a huge consideration if you are downwind of a target likely to be hit by a surface burst. You can experiment on Nukemap with the different options: https://nuclearsecrecy.com/nukemap/ https://nuclearsecrecy.com/nukemap/
  - CapitalistCartr 5y ago
    It hadn't in the Eighties. If you want to be a nuclear war planner, I suggest Nukemap. https://nuclearsecrecy.com/nukemap/ https://nuclearsecrecy.com/nukemap/ No more plastic wheels to spin like a sliderule. Want to take out a target? What's your weapon system's CEP (Circle of Equal Probability)? How is the target built, that is, how much overpressure to destroy it, and how deeply buried is it? Now choose a weapon. If it'a high-priority target, aim more than one weapon at it.
- caf 5y ago
  The fallout by mass isn't primarily the direct daughter products of the fission. It's the thousands of tonnes of pulverised dirt and rock (and concrete and steel and...) that has been neutron-activated and ejected high into the atmosphere.
  - refurb 5y ago
    This was my understanding as well. Radiation levels of daughter products from the weapon drop quite quickly. But the dirt that’s been neutron activated can take a while to come back down and the exposure levels are much higher.
CapitalistCartr 5y ago
Air versus ground is a major factor. In the early days, we targeted whole cities with air bursts, relying on a WWII mentality to warfare. Then, as we gained the ability to target specific military installations, which simultaneously became more hardened, we moved to high ground bursts, then impact bursts, which pretty much means a huge mess. We can easily dig a hole in the ground 60 meters deep, but that means a staggering amount of debris high in the air, some of which will be radioactive.

bouvin 5y ago

For a chilling look at how dirty things can be, I turn your attention to Cobalt Bombs: https://youtu.be/ANIc4NKj6WQ https://youtu.be/ANIc4NKj6WQ

EdwardDiego 5y ago

> Complaints about fall-out vanished, and so did the ability of the international community to monitor weapon design through fall-out analysis But then we get into seismic monitoring, SOSUS, and the infamous "double flash" / Vela Incident. And I totally believe it was the Israeli government testing their nuclear fission weapons with the help of apartheid South Africa. As both were regularly international pariahs, they had a lot of time for each other.

Symmetry 5y ago

In a war many thermonuclear weapons would be targeted at hardened military structures and so detonate close to the ground to maximize local pressure. In a scenario like that you'll get a large amount of fallout just from neutron activation of what was once the ground and the bomb casing won't expecially matter.

mandevil 5y ago

So, where does "dirty" in a nuclear bomb come from? The left behind remnants of fission getting mixed into dust and dirt, then lofted up into the air by the force of the explosion and coming down later downwind- that's fallout, which is the "dirt." Fusion leftover products are essentially fine, and if you explode your bomb high enough that it doesn't throw much dust and dirt into the air that also will limit your fallout (obviously burying deep under the ground also works, but that is generally impossible for a weapon, only matters for tests). One more thing to explain: a typical thermonuclear weapon is actually three stages: fission (the initial atomic bomb) which creates the high temperatures under which we can get fusion, which then gives off roughly an order of magnitude more of energy (second stage) which then hits a natural uranium tamper (third stage) which essentially doubles the amount of energy, at a cost of leaving a lot more fission left-overs around and making it much more dirty. (You can continue to stage indefinitely, but that makes the bomb bigger and less practicable.) The largest weapon ever tested, the so called Czar Bomba, actually had it's third stage uranium replaced with lead, so its energy came all (~97%) from fusion, therefore it had very few fission by-products and was very very clean. This sort of weapon with no third stage tamper is also known as a Neutron Bomb- the so called 'clean bomb' that kills people (with the radiation from the fusion) but mostly leaves buildings intact, and has minimal fallout. So why were neutron bombs scary? For most of the Cold War, when NATO ran exercises, they 'lost' within 2-9 days- where lost means that Soviet armored divisions started running free and unopposed. At which point it became a political question: can NATO use nuclear weapons to wipe away those divisions before they conquer everything? Will the German government allow NATO to use nuclear weapons on German soil- or will the rest of NATO overrule the German chancellors opposition?[1] A neutron bomb, which can kill everyone in a few kilometers with minimal fallout, might be a convincing argument in that situation, and that worried a lot of people about the potential for nuclear escalation. In the post-Cold War context, it is widely believed that the most plausible first use of an American nuclear weapon would be to take out a 'hard' target- one buried deep underground that the US National Command Authority decided needed to be taken out for some reason. That sort of weapon will be extremely dirty, because it will of necessity be right up against the ground, kicking up a lot of dirt and dust and so would have a lot of fallout. Additionally, if you are trying to maximize blast-per-weight or blast-per-dollar, getting rid of that natural uranium tamper is really hard to justify, just to be a bit cleaner to the people who are receiving this weapon. [1]: The first generation French SRBM, the Pluton, had a range of 17-120km, and was based in France- meaning it could only be used to nuke West Germany.