Nuclear Warheads; select-a-yield?

On another forum, some guy who thinks we should “kill 'em all” says our nuclear warheads can be set to a low yield. I’ve never heard of this. Is it possible? Is there some way of controlling the size of the explosion?

Whatever the answer, can you provide a cite? I looked but I’ll be darned if I can find anything on it.

Tells about the development of tactical nukes, and what weapons systems they were built into. For example, there was a class of nukes built as a large shell meant to be delivered via a howitzer. And there’s a tac-nuke warhead that can be mounted onto a tomahawk cruise missile.

Essentially, the size of a nuclear blast depends on how much fuel in the warhead is fissionable (or fusionable). A small amount of explosive would result in a smaller explosion.

I have seen the phrase “dial-a-yield” used with regard to nukes, the impression being that you can, just before launch, say “Hmmm, I’d like 123.87 kilotons today.”

I have no idea how such a mechanism actually works, but I could think of a few possibilities:
[ul][li]Less implosion force on the fissionable core - means less of the fuel undergoes fission.[/li][li]Add/remove fissionable material. This seems trickier, as you’d have to have the conventional explosive stage be adapted to this.[/li][li]Multi-bomb option. You could have, say, 3 fission bombs in one case and choose to detonate 1, 2, or all 3 of them. This seems wasteful, but may be an option in a mass production environment if you have plenty of plutonium to go around.[/ul][/li]
Example of a page with the phrase “dial-a-yield”
Does anyone have any more official info on this?

I’m not a nuclear weapons technician, nor do I play one on TV.

However, I believe the “dial a yeild” is Doug’s option two: Adding or subtracting fissile material.

The key here is the “basic” implosion device- a ball of Plutonium surrounded by a shell of explosives that compresses it to the point of chain reaction- is really just a “sparkplug” these days.

The neutrons and gammas the “primary” puts out, are used to “ignite” a “secondary”- a mass of Uranium, lithium, tritium and other materials. For various reasons, the ‘secondary’ can be many times more powerful than the ‘primary’. I’ve heard of some weapons even having a “third stage” for an even greater yeild.

It’s my understanding the “dial a yeild” is a matter of adding or subtracting something like various “modules” into the secondary.

It’s not a literal “dial” on the side that has an infinite range- I’m pretty sure it’s a matter of “low” (being just the primary, perhaps) “medium” (the primary and a small secondary module) and “high” (the primary and either a large secondary, or possibly more than one small secondary module.)

I gotta post this in a hurry because I’m late… but do a search on dial-a-yeild and I’ll bet you find the info you need.

Basically, as I understand it, at the moment of fission, you can inject tritium (the hydrogen in an H-bomb) into the imploding mass. The amount of tritium you inject controls how large the explosion will be. That’s WAY simplified, of course… if I have time later, I’ll do some research and give you a better answer, assuming someone else doesn’t first…:wink:

From this site they mention the following:

If you search around the site further you’ll find many other weapon descriptions that mention selectable yield as a feature. From this I assume that selectable yield warheads are a common feature of US nuclear weapons.

This page at the same site seems to indicate that how selectable yield warheads are made is still a deep, dark secret while they agreed to admit their existence.

The expression dial-a-yield leaves an impression that there is a continuous range like tuning a radio dial. The existence of a range of discrete choices is far more practical, giving a small, medium, large, extra large range. I suppose a hundredths of a kiloton precision dial is possible, but for weapons of mass destruction, which even a small nuke is, that type of precision is not critical.

As to how, it is a consequence of the precision, and dynamics of geometry in the design of nuclear weapons. By making changes in the timing of the primary, or trigger, or the precise placement, of components in the secondary the amount of material available to sustain a chain reaction, and the length of time during which that reaction can continue can be altered significantly. The energy release of nuclear weapons occurs as a doubling the energy over microsecond range periods of time. The last few microseconds make a lot of difference, and extending those few microseconds can make a very large change in energy. By making a design that incorporates one or more variable adjustments in those things, mostly electronic timing, small differences in configuration can make big differences in yield.

Even at the most efficient, nuclear weapons only convert a small portion of their components into explosive force. So, a deliberately designed inefficiency can give you a variable strength weapon. With nukes, big ones don’t cost much more than little ones, and two of any type represent more expense than one of any type, so, you design for one which can be used as if it were several different types.


" The worst policy is to attack cities. Attack cities only when there is no alternative." ~ Sun-tzu ~

Correct me if I’m wrong, but doesn’t the yield also affect the amount of fallout produced? As in, a lower-yield setting would produce more fallout? (Assuming that you’re not deliberately increasing the fallout in some way.)

Modern nuclear bombs increase their yield through the use of things like beryllium reflectors and tampers and tritium dampers. It’s not hard to imagine that you could adjust the configuration of all these things in order to modify the yield of the weapon.

Nuclear bombs can be made so small that they can wipe out a city block without doing much damage beyond that. Those are the type of weapons that would be used for deep ‘bunker busting’, or for destroying an entire shipyard, or massed armor and troops. I believe some of these smaller weapons were considered for army engineering work as well (i.e. blowing big holes in things to get troops through them).

Back in the 1960’s, the US Army was developing a small nuke called the “Davy Crockett”. This was small enough to be launched from a shoulder-held bazooka! I guess it was powerful enough to level a city block-these would be quite usefull in Afghanistan!

Chronos, I believe fallout is technically under control of weapon construction. I’m sure it isn’t quite as easy to control fallout as it may be to control kiloton yield of a bomb, but in the last thread I was in about nukes (in GD— I believe it was Scylla’s thread) I did link to a cite that had all matter of nuke explanations, including fallout scenarios.

Fallout can never be completely eliminated because even in fusion weapons the secondary stage is still a fission reaction (stage one—>conventional explosive with neutron radiation for stage two—>fission reaction to create pressure for—>stage three, fusion of small weight elements; these “stages” I list are the stage in explosion, not necessarily what nuke heads would call “a three stage nuke” which I believe only cover the numbre of nuclear reactions (like, say, fission-fusion-fission)). Getting the proper efficiency from the fission reaction will enable you to create a bomb where fallout is, IIRC, about 2% of what it would be in a “perfect” fallout weapon (say, a neutron bomb, all of which are supposedly dismantled); for all intents and purposes this is a clean bomb, provided the fallout isn’t in some way poisonous itself, as radiation levels will be almost zero.

Interestingly enough, they can use such ideas to make “dirty” bombs which can essentially create many different radioactive materials (the half-life, of course, is the important part) so that the area of explosion is hot (radioactive-wise) for an almost controlable amount of time.

[digs up cite]Ah, here we are. A very interesting read, if you find this sort of thing interesting. As far as the “fallout” weapons go, this little blurb should catch your interest, Chronos.

It lists the half-life of some of the new isotopes formed in such a reaction:

Cobalt-59     100%        Co-60      5.26 years
Gold-197      100%        Au-198     2.697 days
Tantalum-181   99.99%     Ta-182     115 days
Zinc-64        48.89%     Zn-65      244 days

so in the case of a cobalt jacketed clean nuke (where fission fallout itself is minimized) you could have a heavy fallout area that is safe to enter in a shorter period of time, depending on the spread, etc, etc, but is very hazardous to be in otherwise (like the best of both worlds). Very interesting stuff.

We should note, however, that

Possible, serious weapon design, but apparently not yet realized.

The Davey Crockett and it’s low-yield W-54 warhead have been retired for something like three decades now. It’s tiny little warhead, weighing around 51 pounds, yielded from as little as 10 tons, to as much as 20 tons. Pretty damn small by nuke standards, but more than I’d want the neighbor kid playing with on the 4th of July!

The two main nuclear weapons in the US stockpile, B61 (and variants)and B83 are variable yield designs. They use tritium boosting to control the output of the primary and, thus the ultimate output of the secondary which delivers the bulk of the energy. The tritium is added to the hollow pit of the primary, ether as a permanent capsule, or through a valved delivery which has several settings, form none to all-in. The more Tritium, the bigger the boom. Go to Google and search W80, B61 and B83.

The US Army withdrew its tactical nuclear weapons in the 80s and 90s. Systems that were designed for nuclear weapons or had variants that could utilize them such as the Davy Crockett, Honest John, Nike Hercules/Zeus, Lance, Pershing I & II missiles, artillery shells, demolition munitions, are gone.

The warheads are distinct from the delivery package. The Department of Energy handles the design and production of warheads (with service input). The using service then produces an adaption kit to install the warheads into a delivery system - missile, bomb, torpedo, etc… If a delivery system is withdrawn, the warhead can be re-purposed elsewhere. Having a “standardized” warhead design reduces development costs. Different Strategic Arms Limitation Treaties required the disassembly of significant numbers of the older warheads to reach negotiated limits.

Methods used to create delectable yields are classified. What you read on-line is speculative.

Zombie alert. This is from 2001.

Even though it’s a zombie, it’s nice that it was re-animated with a correct answer.
Tritium injection is the key. Since these warheads are “boosted fission,” they derive a large part of their yield from the additional fission of a U-238 tamper, caused by fast neutrons from D-T fusion in the “Pit.” If the amount of D-T is reduced to zero, the device becomes a pure fission weapon, resulting in a fraction of the possible yield.

And in the years since 2001 at least one great book covering this subject has been published:

Command and Control: Nuclear Weapons, the Damascus Accident, and the Illusion of Safety by Eric Schlosser

This book covers all kinds of nuclear weapon design concerns, discussion tritium injection, sealed pit bombs, various safety measures, and plenty of other topics. It’s an eye opener.

And the cover looks like a beat up old military manual. How cool is that?

And there are some excellent videos on the subject from the Harvard Kennedy School for Science and Technology:

Very interesting discussion of many aspects of the whole nuclear weapons industry.

Have you people never heard of wikipedia? Sure, it’s not to be cited in college research papers, but gives a pretty good idea of a concept.

This thread was started in 2001, at that time Wikipedia had barely been founded.