8 ms·

This is old cold-war spin, and it has been refuted so many times, yet it still surfaces. Read "The curve of binding energy", and you will learn from Ted Taylor

by phkamp 13y ago

This is old cold-war spin, and it has been refuted so many times, yet it still surfaces. Read "The curve of binding energy", and you will learn from Ted Taylor, one of the worlds best nuclear warhead designers, that you can make the simplest atomic bomb by dropping one piece of fissile material on another, provided they are big enough to become a critical mass. It won't be tens of megatons, but it will be a perfect terror weapon, spreading panic, making a large-ish area uninhabitable and costing a fortune and many years to clean up. If the terrorists are smart enough bring a couple of sacks of salt, it makes the mess much worse. There are damn good reasons to go out of the way to prevent access to the funny end of the periodic table.

srean 13y ago
More qualified people will correct me, but I think there is more to it than dropping a piece of fissile material over another. I think the trick is to keep the pieces together long enough before the forces of explosion rips them apart. As far as I know there have been several examples of accidents were scientists did actually drop a fissile blob over another, and the material did go critical, but thankfully the scientist(s) involved were fast enough to separate the pieces so that no catastrophes ensued. They themselves died as a result of exposure to radiation. As I said, more qualified people will be able to fill in the details and citations.
- louthy 13y ago
  I suspect you're referring to this: https://en.wikipedia.org/wiki/Louis_Slotin#Criticality_accident https://en.wikipedia.org/wiki/Louis_Slotin#Criticality_accid... "At 3:20 p.m., the screwdriver slipped and the upper beryllium hemisphere fell, causing a "prompt critical" reaction and a burst of hard radiation. At the time, the scientists in the room observed the blue glow of air ionization and felt a heat wave. In addition Slotin experienced a sour taste in his mouth and an intense burning sensation in his left hand. Slotin jerked his left hand upward, lifting the upper beryllium hemisphere and dropping it to the floor, ending the reaction. However, he had already been exposed to a lethal dose of neutron radiation."
  - caf 13y ago
    That wasn't even the first fatal criticality incident involving that particular plutonium core (known as the "Demon Core"). Funnily enough, I submitted an interesting article just a few hours ago on the history of this core: https://news.ycombinator.com/item?id=6229011 https://news.ycombinator.com/item?id=6229011
- 6d0debc071 13y ago
  > More qualified people will correct me, but I think there is more to it than dropping a piece of fissile material over another “With modern weapons-grade uranium, the background neutron rate is so low that terrorists, if they have such material, would have a good chance of setting off a high-yield explosion simply by dropping one half of the material onto the other half. Most people seem unaware that if separated HEU [Highly Enriched Uranium] is at hand it’s a trivial job to set off a nuclear explosion … even a high school kid could make a bomb in short order.” - Luis Alvarez, Nobel Laureate in Physics, 1988 The key being, as I understand it, actually getting weapons-grade material of sufficient purity. Though the actual design of a practical, controlled and efficient, weapon would doubtless be more somewhat more complex. For which the n-th country project is well worth reading about: http://www.theguardian.com/world/2003/jun/24/usa.science http://www.theguardian.com/world/2003/jun/24/usa.science
  - fitumpich 13y ago
    That is correct. i work in nuclear material security and safeguards. For what I can say, which isn't much, it's the security of the material (HEU and Pu) that makes it hard to make a bomb. Its hard to enrich, and furthermore you need HEU or Pu. LEU won't get you a big boom. Without enough enrichment, no Bomb. Theft and diversion is a big deal with Pu and HEU for this very reason. Which is why access to either has a two man rule. And because you can safely handle Pu and HEU,(its just an alpha and criticality hazard so unless you inhale or eat them, or you have bad geometry it's no big deal), that makes it vital that you carefully account for all of it. It won't kill the thief, and you don't need much Pu for a bomb.
- deleted 13y ago
  [deleted]
- marvin 13y ago
  I'm sure a physicist can get the details of this better than I can, but I'm pretty sure it's sufficient to create a subcritical, hollow sphere of fissile material and then slam a matching sphere of fissile material into it very fast. The "very fast" portion could be accomplished with a steel pipe and explosives. The manufacturing would certainly be within the capability of a reasonably skilled group of insurgents/freedom fighters. The big question is where they'd get the fissile material.
Amadou 13y ago
you can make the simplest atomic bomb by dropping one piece of fissile material on another, provided they are big enough to become a critical mass. My understanding of Ted Taylor's claims about compact fission bombs is that, absent high-grade manufacturing processes to properly shape the fissile material, we are looking at a couple of hundred kilograms to achieve critical mass. Actual "suitcase nukes" in the 10-20 kilogram range require perfectly shaped components and are also very high maintenance due to their electronics degrading rapidly from such close proximity to radiation sources. Then there is the question of testing. They say you can recognize veteran bomb makers by their missing fingers because they don't get things right the first time. Any testing of a fission bomb anywhere in the world is going to be noticed by seismographs at the very least.
- archgoon 13y ago
  Why is testing an issue? The Trinity test was successful on the first run. Nation-states only conduct tests to calibrate destructive capabilities and fallout effects (a non-issue if you just want a big boom) and signal to other nation-states 'Don't mess with me'. Furthermore, states such as Israel, are believed to be nuclear, without ever having conducted any (known) tests. An unsuccessful nuclear explosion would just be a dirty bomb, which would still have the desired effects from a terrorist attack perspective. So there's no real reason to test before hand.
  - Amadou 13y ago
    In the case of a ultra-simple design available to terrorists that reaches critical mass by simply "dropping" one chunk of fissile material on another there is no explosion if it doesn't actually reach critical mass. Israel is a nation-state with a lot more resources available to it like the ability to measure purity and to conduct simulations. In fact a key part of nuclear politics for the last 20 or so years has been super-computer based simulations in lieu of testing. In the US the programs have been responsible for the construction of some of the largest super-computers of their time(s). https://en.wikipedia.org/wiki/Accelerated_Strategic_Computing_Initiative https://en.wikipedia.org/wiki/Accelerated_Strategic_Computin...
rdl 13y ago
I think a dirty bomb would be more than "scary" enough, given general anti-nuclear phobia, and is still objectively far easier than even a simple gun-type weapon. OTOH, I'm pretty sure I could build a gun-type weapon with pretty modest resources. More than Kickstarter, less than $50mm. The hard part would just be doing it in secret, especially since there are dual-use controls and people trying to actively find people making covert weapons. However, almost all nonproliferation controls are still based around restricting access to fissile material; if you solved that, I'd be comfortable doing this in a third-tier US city (away from the border), maybe in an old mine.
- tlrobinson 13y ago
  "Kickstarter for Terrorists" is terrifying prospect. But also slightly amusing, I'd like to see a parody done.

by phkamp 13y ago

srean 13y ago

More qualified people will correct me, but I think there is more to it than dropping a piece of fissile material over another. I think the trick is to keep the pieces together long enough before the forces of explosion rips them apart. As far as I know there have been several examples of accidents were scientists did actually drop a fissile blob over another, and the material did go critical, but thankfully the scientist(s) involved were fast enough to separate the pieces so that no catastrophes ensued. They themselves died as a result of exposure to radiation. As I said, more qualified people will be able to fill in the details and citations.

louthy 13y ago
I suspect you're referring to this: https://en.wikipedia.org/wiki/Louis_Slotin#Criticality_accident https://en.wikipedia.org/wiki/Louis_Slotin#Criticality_accid... "At 3:20 p.m., the screwdriver slipped and the upper beryllium hemisphere fell, causing a "prompt critical" reaction and a burst of hard radiation. At the time, the scientists in the room observed the blue glow of air ionization and felt a heat wave. In addition Slotin experienced a sour taste in his mouth and an intense burning sensation in his left hand. Slotin jerked his left hand upward, lifting the upper beryllium hemisphere and dropping it to the floor, ending the reaction. However, he had already been exposed to a lethal dose of neutron radiation."
- caf 13y ago
  That wasn't even the first fatal criticality incident involving that particular plutonium core (known as the "Demon Core"). Funnily enough, I submitted an interesting article just a few hours ago on the history of this core: https://news.ycombinator.com/item?id=6229011 https://news.ycombinator.com/item?id=6229011
6d0debc071 13y ago
> More qualified people will correct me, but I think there is more to it than dropping a piece of fissile material over another “With modern weapons-grade uranium, the background neutron rate is so low that terrorists, if they have such material, would have a good chance of setting off a high-yield explosion simply by dropping one half of the material onto the other half. Most people seem unaware that if separated HEU [Highly Enriched Uranium] is at hand it’s a trivial job to set off a nuclear explosion … even a high school kid could make a bomb in short order.” - Luis Alvarez, Nobel Laureate in Physics, 1988 The key being, as I understand it, actually getting weapons-grade material of sufficient purity. Though the actual design of a practical, controlled and efficient, weapon would doubtless be more somewhat more complex. For which the n-th country project is well worth reading about: http://www.theguardian.com/world/2003/jun/24/usa.science http://www.theguardian.com/world/2003/jun/24/usa.science
- fitumpich 13y ago
  That is correct. i work in nuclear material security and safeguards. For what I can say, which isn't much, it's the security of the material (HEU and Pu) that makes it hard to make a bomb. Its hard to enrich, and furthermore you need HEU or Pu. LEU won't get you a big boom. Without enough enrichment, no Bomb. Theft and diversion is a big deal with Pu and HEU for this very reason. Which is why access to either has a two man rule. And because you can safely handle Pu and HEU,(its just an alpha and criticality hazard so unless you inhale or eat them, or you have bad geometry it's no big deal), that makes it vital that you carefully account for all of it. It won't kill the thief, and you don't need much Pu for a bomb.
deleted 13y ago
[deleted]
marvin 13y ago
I'm sure a physicist can get the details of this better than I can, but I'm pretty sure it's sufficient to create a subcritical, hollow sphere of fissile material and then slam a matching sphere of fissile material into it very fast. The "very fast" portion could be accomplished with a steel pipe and explosives. The manufacturing would certainly be within the capability of a reasonably skilled group of insurgents/freedom fighters. The big question is where they'd get the fissile material.

Amadou 13y ago

you can make the simplest atomic bomb by dropping one piece of fissile material on another, provided they are big enough to become a critical mass. My understanding of Ted Taylor's claims about compact fission bombs is that, absent high-grade manufacturing processes to properly shape the fissile material, we are looking at a couple of hundred kilograms to achieve critical mass. Actual "suitcase nukes" in the 10-20 kilogram range require perfectly shaped components and are also very high maintenance due to their electronics degrading rapidly from such close proximity to radiation sources. Then there is the question of testing. They say you can recognize veteran bomb makers by their missing fingers because they don't get things right the first time. Any testing of a fission bomb anywhere in the world is going to be noticed by seismographs at the very least.

archgoon 13y ago
Why is testing an issue? The Trinity test was successful on the first run. Nation-states only conduct tests to calibrate destructive capabilities and fallout effects (a non-issue if you just want a big boom) and signal to other nation-states 'Don't mess with me'. Furthermore, states such as Israel, are believed to be nuclear, without ever having conducted any (known) tests. An unsuccessful nuclear explosion would just be a dirty bomb, which would still have the desired effects from a terrorist attack perspective. So there's no real reason to test before hand.
- Amadou 13y ago
  In the case of a ultra-simple design available to terrorists that reaches critical mass by simply "dropping" one chunk of fissile material on another there is no explosion if it doesn't actually reach critical mass. Israel is a nation-state with a lot more resources available to it like the ability to measure purity and to conduct simulations. In fact a key part of nuclear politics for the last 20 or so years has been super-computer based simulations in lieu of testing. In the US the programs have been responsible for the construction of some of the largest super-computers of their time(s). https://en.wikipedia.org/wiki/Accelerated_Strategic_Computing_Initiative https://en.wikipedia.org/wiki/Accelerated_Strategic_Computin...

rdl 13y ago

I think a dirty bomb would be more than "scary" enough, given general anti-nuclear phobia, and is still objectively far easier than even a simple gun-type weapon. OTOH, I'm pretty sure I could build a gun-type weapon with pretty modest resources. More than Kickstarter, less than $50mm. The hard part would just be doing it in secret, especially since there are dual-use controls and people trying to actively find people making covert weapons. However, almost all nonproliferation controls are still based around restricting access to fissile material; if you solved that, I'd be comfortable doing this in a third-tier US city (away from the border), maybe in an old mine.

tlrobinson 13y ago
"Kickstarter for Terrorists" is terrifying prospect. But also slightly amusing, I'd like to see a parody done.