What is the smallest nuclear weapon?

[benzman]

In terms of TNT equivalent yield, what is the smallest viable nuclear weapon?  One that will detonate rather than just fizzle.  I am prompted to ask by talk of 'tactical' weapons.  To my mind, nuclear weapons are so phenomenally destructive that their only viable use is to destroy a city and annihilate as many of that city's people as possible.  So to me, the only use for nuclear weapons is deterrence,  something that they did brilliantly in the cold war, and any talk of using them tactically is ridiculous. I will be interested to read any comments on this subject.

[mikegarrison]

https://en.wikipedia.org/wiki/W54

The US once had a nuclear weapon designed to be fired by infantry soldiers.

[Gargamel]

24 minutes ago, mikegarrison said:

https://en.wikipedia.org/wiki/W54

The US once had a nuclear weapon designed to be fired by infantry soldiers.

Ah yes, the Davy Crockett.    The nuclear weapon that was fired from a recoilless rifle, with a max range of 2 miles.   Which meant it shot far enough that it wasn’t usually dangerous to the crew firing it.    Yet however it was found to be too inaccurate to be considered reliable enough to hit a target even with a nuclear  weapon as ammo.  

[kerbiloid]

Spoiler

 

 

Unless this is not a fake bag.

Spoiler

 

[DDE]

3 hours ago, benzman said:

In terms of TNT equivalent yield, what is the smallest viable nuclear weapon?  One that will detonate rather than just fizzle.  I am prompted to ask by talk of 'tactical' weapons.  To my mind, nuclear weapons are so phenomenally destructive that their only viable use is to destroy a city and annihilate as many of that city's people as possible.  So to me, the only use for nuclear weapons is deterrence,  something that they did brilliantly in the cold war, and any talk of using them tactically is ridiculous. I will be interested to read any comments on this subject.

In the late 1990s-early aughts, after seeing the pricetages for modern PGMs, there was a spate of interest in fourth-generation pure fusion weapons that wouldn't have a minimum yield.

This answer looks credible: https://www.quora.com/What-is-the-smallest-nuclear-explosion-possible/answer/William-Mook?ch=15&oid=211270801&share=84e71fa0&target_type=answer

More importantly, kiloton-class nuclear weapons aren't that destructive. This is more or less representative of a nuclear artillery shell: https://nuclearsecrecy.com/nukemap/?&kt=1&lat=55.751667&lng=37.617778&hob_psi=5&hob_ft=1025&casualties=1&psi=20,5,1&zm=12

[kerbiloid]

In terms of TNT, rather low and rather simple.

https://www.sciencealert.com/the-chilling-story-of-the-demon-core-and-the-scientists-who-became-its-victims

Spoiler

 

[TheSaint]

Don't forget the portable application of the W54, the Special Atomic Demolition Munition. 70 pounds, designed to be carried by a single soldier. Variable yield between 10 and 1,000 tons of TNT. (Tons, not kilotons.)

[Bej Kerman]

18 hours ago, Gargamel said:

too inaccurate to be considered reliable enough to hit a target even with a nuclear  weapon as ammo

Sounds more like a skill issue than a nuke issue 

Edited May 18, 2022 by Bej Kerman
grammar

[adsii1970]

My favorite was the Soviet Union's "suitcase nuclear bombs." Some are still missing to this day.

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

https://nonproliferation.org/suitcase-nukes-a-reassessment/

 

[SunlitZelkova]

22 hours ago, benzman said:

To my mind, nuclear weapons are so phenomenally destructive that their only viable use is to destroy a city and annihilate as many of that city's people as possible.  So to me, the only use for nuclear weapons is deterrence,  something that they did brilliantly in the cold war, and any talk of using them tactically is ridiculous.

Depending on situation they can be viable for use in a tactical manner. The most realistic scenario would be attacking a carrier battle group. Soviet ASMs had the option of carrying a 200-300 kiloton warhead. Another would be if the enemy is* restricted to advancing through a relatively small area like the Fulda Gap.

Another “tactical” use would be attacking the enemy’s logistics train/area. I don’t know just how spread out those can be though, so it could take quite a few weapons.

*just because one thinks the enemy is restricted to advancing through a certain area doesn’t mean they are. See the Ardenne in 1940.

[Gargamel]

5 hours ago, adsii1970 said:

My favorite was the Soviet Union's "suitcase nuclear bombs." Some are still missing to this day.

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

https://nonproliferation.org/suitcase-nukes-a-reassessment/

 

My favorite were the chicken powered nuclear land mines. 

[kerbiloid]

1 hour ago, Gargamel said:

My favorite were the chicken powered nuclear land mines. 

After the British "keep the bomb overturned to prevent the accidental arming" and "fully arm the bomb on ground before the plane engines are on", it's normal.

 

Edited May 19, 2022 by kerbiloid

[sevenperforce]

16 hours ago, adsii1970 said:

My favorite was the Soviet Union's "suitcase nuclear bombs." Some are still missing to this day.

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

https://nonproliferation.org/suitcase-nukes-a-reassessment/

The smallest size you can make a fission weapon, in terms of radius, is constrained by nuclear physics to around 6 inches, the size of the physics package on the W48.

That's because you need to be able to form more than just a critical mass; you need a prompt-supercritical mass, or the weapon will fizzle. A solid sphere of plutonium-239 can be exactly critical at a little under 4 inches in diameter, but you can make it prompt-supercritical using high explosives with a heavy tamper to compress it to a significantly higher density.  That's how the Gadget (Trinity) and Fat Man (Nagasaki) functioned:

However, the requisite arrangement of high explosive lenses made the overall physics packages in those bombs around 5 feet in diameter:

One of the reasons these were so big is that we had very little plutonium available when these bombs were being built. To build a smaller bomb, you actually need more plutonium, kept subcritical by being in a non-spherical shape. You can then use two-point linear implosion to reshape the subcritical ovoid fissile pit into a prompt-supercritical sphere with less compression (and, IIRC, no tamper at all):

Spoiler

This design is considered to be less efficient because it uses more fissile material, but it allows extremely small diameters. The smallest known weapon is the W48 at 6.1 inches in diameter (that's 155 mm), as shown below in the center:

It should be theoretically possible to get a diameter as low as 4-5 inches by using even more plutonium in a very thin oval shape, but the physics to ensure precise linear implosion becomes extremely difficult and the likelihood of a fizzle goes up. A "suitcase nuke" is quite realizable, while a "briefcase nuke" is probably on the edge of what's possible.

If there was a denser fissile fuel then it would be possible to make it smaller, but the only known fissile nuclides are uranium-233, uranium-235, and plutonium-239. Plutonium is slightly denser than uranium.

[sevenperforce]

On 5/18/2022 at 1:14 AM, kerbiloid said:

Unless this is not a fake bag.

  Hide contents

I believe those are understood to be dirty bombs, i.e., conventional-explosive radiological dispersal devices.

Here's another image of the W48 (or, a scale model of it) to demonstrate size:

On 5/17/2022 at 10:38 PM, benzman said:

I am prompted to ask by talk of 'tactical' weapons.  To my mind, nuclear weapons are so phenomenally destructive that their only viable use is to destroy a city and annihilate as many of that city's people as possible.  So to me, the only use for nuclear weapons is deterrence,  something that they did brilliantly in the cold war, and any talk of using them tactically is ridiculous.

NATO has virtually no use for tactical nuclear weapons today. However, during the Cold War, the sheer volume of ground forces that the Soviet-led Warsaw Pact could have thrown at western Europe would have overrun NATO's defenses, even though NATO equipment and training was generally far superior. Accordingly, NATO was prepared to use low-yield tactical nuclear weapons against Pact ground forces to blunt any invasion, both as a battlefield deterrent and through area denial. Ground troops can't march through a radioactive wasteland.

Why make tactical nuclear weapons with lower yield than conventional-explosive weapons? Well, weapons like the Davy Crockett weren't designed for their yield at all, but for their radioactive capabilities. A Cold-War era tank has sufficient armor to survive virtually all conventional high-explosive munitions; you need to hit them precisely with a shaped-charge explosive or kinetic penetrator to actually destroy them. A nuclear fireball from a W54 doesn't have significantly more energy than a conventional high-explosive munition, but it DOES produce a massive burst of neutrons that would fry the troops inside a tank, even though the tank itself would survive.

Today, the United States only has around 230 remaining weapons in the tactical class, around 4% of its total stockpile. And even those are only considered tactical because they are dial-a-yield and thus can be deployed tactically OR strategically depending on the situation.

[kerbiloid]

45 minutes ago, sevenperforce said:

I believe those are understood to be dirty bombs, i.e., conventional-explosive radiological dispersal devices.

Iirc, the author of the webpage about the DPRK nuke/missile program, which I had linked in the "Chinese space" thread, and which is currently down but available in webarchive, thinks that it may be a (obviously a mockup at the parade) gub-scheme mini-nuke on pure ²³⁹Pu, and thus tiny.

While it's a bad idea to implement a ThinMan-like gun-scheme on Pu due to the parasite activity of ²⁴⁰Pu, an early extraction of irradiated fuel somehow allows to get more pure ²³⁹Pu which allows to make an ineffective but compact gun-scheme punuke instead of usual unuke.

He presumes, this may be it, just a little dramatically presented.
(On the other hand, if a hundred of Korean paratroopers in camouflage with similar cases land in your city, how can you know which one carries a real nuke among the mockups).

Also, another webpage, of some (US ?) veteran organization in its long article about 5th gen nukes describes how good and compact are the subcritical nukes giving tonnes or less of TNT yield (like a failed classic nuke, but failed intentionally).

As both options (the Pu-gun-nuke (pugunuke?) and the subcritical one-point nuke (semi-swan nuke? semiswanuke?) ) approach to something looking very similar, maybe it's a mockup of a prototype of a real thermos flask nuke.

Even if not use Americium instead of Pu.

1 hour ago, sevenperforce said:

That's how the Gadget (Trinity) and Fat Man (Nagasaki) functioned:

Has nothing common with reality for decades. The two-point ones (the swan design brought by you on the picture and its Soviet analog) were used since late 1950s, instead of these bulky lenses.

[magnemoe]

1 hour ago, sevenperforce said:

The smallest size you can make a fission weapon, in terms of radius, is constrained by nuclear physics to around 6 inches, the size of the physics package on the W48.

That's because you need to be able to form more than just a critical mass; you need a prompt-supercritical mass, or the weapon will fizzle. A solid sphere of plutonium-239 can be exactly critical at a little under 4 inches in diameter, but you can make it prompt-supercritical using high explosives with a heavy tamper to compress it to a significantly higher density.  That's how the Gadget (Trinity) and Fat Man (Nagasaki) functioned:

However, the requisite arrangement of high explosive lenses made the overall physics packages in those bombs around 5 feet in diameter:

One of the reasons these were so big is that we had very little plutonium available when these bombs were being built. To build a smaller bomb, you actually need more plutonium, kept subcritical by being in a non-spherical shape. You can then use two-point linear implosion to reshape the subcritical ovoid fissile pit into a prompt-supercritical sphere with less compression (and, IIRC, no tamper at all):

  Hide contents

This design is considered to be less efficient because it uses more fissile material, but it allows extremely small diameters. The smallest known weapon is the W48 at 6.1 inches in diameter (that's 155 mm), as shown below in the center:

It should be theoretically possible to get a diameter as low as 4-5 inches by using even more plutonium in a very thin oval shape, but the physics to ensure precise linear implosion becomes extremely difficult and the likelihood of a fizzle goes up. A "suitcase nuke" is quite realizable, while a "briefcase nuke" is probably on the edge of what's possible.

If there was a denser fissile fuel then it would be possible to make it smaller, but the only known fissile nuclides are uranium-233, uranium-235, and plutonium-239. Plutonium is slightly denser than uranium.

Well the blast from that 155 mm shell was only 72 ton tnt, now that is simlar to some huge fuel air bombs while this is an standard artillery shell. 
Now this could been converted to an suitcase nuke as it only weight 55 kg and lots of that is the artillery shell itself. 
An 44 kg shell with 2 KT blast was under planning at the end of the cold war. https://en.wikipedia.org/wiki/W82

I belie most nuclear bombs today only uses two detonator. but they uses an advanced mix of explosives to shape the shock wave to create an circular compression. 
They also has far more room to work with. Two fuses is important as they has to be triggered at the same time to set of the nuke making an accident very unlikely, now it could be more than two but its not a lot like the first bombs because better explosives who can be manufactured with very high accuracy. 
 

[steve9728]

On 2022/5/18 at AM6点14分, kerbiloid said:

Unless this is not a fake bag.

There have been rumours on the Chinese folk internet that this neighbour of ours often buys clothes or something from us for 'parties' and rarely pays for it.

Davy, guys, we forget Davy (and Annie)

Edited May 19, 2022 by steve9728

[benzman]

Some very good reading here. Many thanks to all who have contributed.

[SunlitZelkova]

6 hours ago, sevenperforce said:

Ground troops can't march through a radioactive wasteland.

They can with NBC protection. The Soviets did this during Operation Snezhok in 1954.

Of course, just because they can doesn’t mean they should.

[kerbiloid]

17 hours ago, sevenperforce said:

Ground troops can't march through a radioactive wasteland.

Of course they can.

Spoiler

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

And similar exercises by the USSR, UK, France, and China.

Upd.
A quick-found description.
https://judgesuhov-livejournal-com.translate.goog/97394.html?_x_tr_sl=auto&_x_tr_tl=en&_x_tr_hl=ru

Upd2.

Spoiler

 

 

Edited May 20, 2022 by kerbiloid

[DDE]

17 hours ago, sevenperforce said:

Ground troops can't march through a radioactive wasteland.

Hence the Soviet policy of total mechanization.

17 hours ago, sevenperforce said:

A nuclear fireball from a W54 doesn't have significantly more energy than a conventional high-explosive munition, but it DOES produce a massive burst of neutrons that would fry the troops inside a tank, even though the tank itself would survive.

Soviet tanks are known to have had anti-neutron applique armor long before ERWs were fielded. All tests demonstrated a depressing ineffectiveness of neutron bombs; even if a fatal dose was achieved, the crews were likely to turn into "walking dead" - the dose needed to kill a human on the spot is truly enormous, between 40 and 120 Sv.

Spoiler

A bad plan all around

 

In practice, neutron weapons became a rhetorical tool ("capitalist weapons"), and found their true use in missile defense. More importantly, all small thermonukes are neutron bombs due to inferior tamper design.

[kerbiloid]

There is a special unit for that.

https://store.steampowered.com/app/356270/Cuban_Missile_Crisis/?l=russian

Spoiler

 

10 minutes ago, DDE said:

even if a fatal dose was achieved, the crews were likely to turn into "walking dead" - the dose needed to kill a human on the spot is truly enormous, between 40 and 120 Sv.

And several weeks after getting a lethal but not smashing dose of several Sv, the humans feel healthy, as acute symptomes caused by immediate mass death of cells have passed, while the lethal hypoxia caused by absence of functioning bone marrow needs several months to develop.

So, the lethally irradiated but not fallen dead soldiers have from several weeks to several months to be used as a suicidal trooper, knowing that he is already dead, but effectively fighting.