What is the weakest possible full nuclear weapon?

[chuck]

There are some information that Russians will equip some of their ICBMs with micro (in yield, not size) nukes with yield of equivalent to 50 tons of TNT. The idea was to allow the weapon to make a pinpoint strike with enough power to ensure target destruction, but still be weak enough so it can be said to be almost quasi-conventional and thus not provoke responses commensurate with a full nuclear strike. This raise the issue of what is the smallest practical yield for a nuclear weapon? The fact the nuclear weapons all require some sort of critical mass to initiate fission at early stage means there must be some minimum engineering limit to the power of a nuclear weapons. what is it? I use to think it was close to 1 kiloton, not 50 tons.

[Seasick]

Not sure how to do it. It would obviously be fission only. The US can hit a target close enough to the aim point to use conventional warheads. The WBush administration also is considering building small nukes like this. The small nuke thing will be canceled no matter who wins the the election this fall. I think for the US making more powerful conventional explosives would be easier.

[Werner]

I think the new explosive technology used (for example) in explosively formed projectiles has the potential to produce sufficient pressure densities in properly shaped subcritical quantities of fissile materials. This is termed a "prompt critical" configuration.

In fact, I can imagine a configuration where a "ripple" of plastic explosives maintains the critical density for some protracted time, until the radiation pressure overwhelms the concussive effect. Once criticality is achieved, a quantity of deuterium could amplify the nuclear reaction to whatever yield is desired.

It could also be done by using exotic fissile materials. For example, the quantity of neptunium-236 necessary is 7 kg, corresponding to a mass of 8.7 cm in size. An implosion device would require even less (perhaps as much as 10% less). The amount of uranium-235 required for criticality is 52 kg, corresponding to a sphere 17 cm in diameter.

Note that neutron and x-ray reflectors can reduce the amount of material necessary to start and propagate a chain reaction.

This is really not so much a physics problem as much as a computation, electrical engineering and machining problem.

[chuck]

Increase in physical density without lowering temperature is equivalent to increase in energy density. If you increase the physical density of fissile material using explosive compression, the final energy density of the fissile material can not exceed the original energy density of the explosive material, according to law of thermal dynamics. So given that energy density in chemical explosives are finite, there must be a limit to the magnitude of increase in fissile material's energy and physical density that can be extracted with each type of explosive, regardless of the amount of explosive involved. So fissile material can be compressed to a degree, but not indefinitely compressed, by clever tricks in computation, electric engineering or mechanical engineering. So there must still be a minimum theoretical limit to explosive yield of a fission device.

[chuck]

In any case, the availability to 50 ton yield nuclear weapons is scary. By creating types of nuclear weapon that are attractive to use in situations where previously no nuclear weapon usage would have been contemplated, it increases the slipperiness of any war involving nuclear armed powers, and increases the likelihood that hostility situation will get out of hand and trigger usages of much larger nuclear weapons.

[Werner]

It is my understanding that subkiloton warheads have existed for some time. There were exotic devices on the table at the end of the Reagan Administration which could be used as land mines or torpedo warheads, with the bulk of the explosive force "directional" away from the projector (how this is accomplished is beyond my understanding).

In 1992, Secretary Cohen testified about subkiloton nuclear explosions used for underground testing of communications equipment, but there is no indication of how this was accomplished.

The man-portable Special Atomic Demolition Munition (SADM) is supposed to be in the subkiloton range, as was the Davy Crockett gun's 51 pound W-54, which was rated at 0.18Kt, or 18 tons (discounting radiation effect).

[Dave Wooley]

What ever size of yield the by product of such a device will be radiation and fall out . The question should be by how much and how far. So in theory there is no such thing as a weak nuclear weapon
Dave Wooley

[Walt]

We carried MK 45 Torpedos with Astor loads (Low Yield Tach Nuke warhead) in late 60s and early 70s.. I understand that these were removed in late 70s and were given conventional warheads. Back then there were several different (Tactical Nuke Weapons) in the US inventory. I believe the SALT II agreements eliminated many of them.

[chuck]

...Davy Crockett gun's 51 pound W-54, which was rated at 0.18Kt, or 18 tons ...

0.18Kt is 180 tons.

[Werner]

...Davy Crockett gun's 51 pound W-54, which was rated at 0.18Kt, or 18 tons ...

0.18Kt is 180 tons.

I quoted the article at Globalsecurity. Wikipedia lists the W-54 as having different marks with yields from 10 tons to 250 tons (as fit to the Falcon AAM).

[chuck]

0.18 Kilotons is still 180 tons, not 18 tons.

[chuck]

I wonder if the extremely low yield weapons achieved their small yield by intentionally mistiming their detonation sequence, and thus intentionally achieving a fizzled explosion in a manner similar to the unintended North Korean test dud from 2006. The NK test registered only 250 tons according to some sources.

[Werner]

That would be a very uncertain and way of doing it, probably leading to random results. The easiest way is to use subcritical assemblies and moderate the explosion by varying the quality of neutron reflectors or the amount of fissile fuel.

If the whole warhead, fully equipped, weighs 70 pounds, the amount of fissile material must be under 10 pounds.

[Seasick]

Small nukes like this are a waste. Figuaring out a new form of high explosive and building it would undoubtly cost only a fraction.

[akojanov]

There are some information that Russians will equip some of their ICBMs with micro (in yield, not size) nukes with yield of equivalent to 50 tons of TNT. The idea was to allow the weapon to make a pinpoint strike with enough power to ensure target destruction, but still be weak enough so it can be said to be almost quasi-conventional and thus not provoke responses commensurate with a full nuclear strike. This raise the issue of what is the smallest practical yield for a nuclear weapon? The fact the nuclear weapons all require some sort of critical mass to initiate fission at early stage means there must be some minimum engineering limit to the power of a nuclear weapons. what is it? I use to think it was close to 1 kiloton, not 50 tons.

Hello!

I'm from Russia, Moscow . On military forums in Russia discussing this question. The common words: we (and you, of course!) have ways to produce the 7,62 mm nuclear bullet with 1k TNT eq, but price and another reasons (env. temp., storage precautions, fire speed, etc) make this project not real. If You interesting this - try search any information about Californium.

WBR, Alex Kojanov

PS. Sorry my English...

PPS. Russians come , is not?

[richter111]

Welcome aboard!

We have several Ukrainian, Russian and a Belarus or two I believe on board! Everyone is welcome..

(Except for Marty, but thats a whole different story! )

Ric

[JWintjes]

Back from the woods and one of the first things I have to do is agree with Chuck - scary indeed...

I find the operational implications of such weapons highly problematical. They not only lower the threshold for the employment of higher-yield weapons, one also wonders whether they are tactical or strategic, so to speak, assets. If the former, which level in the chain of command can authorize their employment? If the latter, is then the attack on such a weapon comparable to an attack on any other strategic asset - would hitting a SPG loaded with suitable shells be the same as taking out a boomer? In short, apart from the really interesting engineering question I seriously doubt the reasoning behind micronukes.

Jorit

[chuck]

Back from the woods and one of the first things I have to do is agree with Chuck - scary indeed...

Jorit

So Jorit, which do you think would be the means by which the world would be ended? A nuclear escalation started by careless use of mico-nukes, or an agreement between the two of us that sunders all known laws of nature?

Welcome back.

[JWintjes]

So Jorit, which do you think would be the means by which the world would be ended? A nuclear escalation started by careless use of mico-nukes, or an agreement between the two of us that sunders all known laws of nature?

Welcome back.

Uh, probably both - wait, it has already started......



Jorit

[Seasick]

Mini nukes are a security threat no matter how well protected. That was the opinion of the Reagan administration. They scrapped all the mini nukes in the arsenal and didn't replace them. Without a loon like Rumsfeld or McNamera at DoD I doubt that any more will be built.