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Dial-a-Yield Nukes: Regular or Extra-Crispy

Article #125 • Written by Alan Bellows

In regards to nuclear weaponry, a kiloton is equivalent to the explosive destructive power 1,000 metric tons of TNT. Most tactical nuclear weapons in operational deployment today have yields measured in tens or hundreds of kilotons, which tends to make them overkill for any kind of tactical use.

Consider, for example, the fact that Hiroshima was leveled by a 13 kiloton weapon, resulting in an estimated 80,000 deaths. By comparison, the modern W80 nuclear warhead-- one of the most common in U.S. active deployment-- has a maximum yield of about 150 kilotons. This weapon is so powerful that it can completely wipe out a typical medium-sized city, but at the flick of a switch, the warhead's potency can be reduced to as little as five kilotons. This handy feature is called Dial-a-Yield, and it allows nuclear stockpiles to take advantage of the one-size-fits-all approach.

In some cases, weapon yields are adjusted prior to use by replacing portions of the fissile material with lead tampers, thereby reducing the potency. One such weapon was Tsar Bomba, the most powerful bomb ever exploded, which was dialed down to 50 megatons from its maximum of 100 megatons by replacing a fission stage with lead. But modern nuclear missiles can be remotely adjusted to the desired destructive power, even while the weapon is in flight.

The key to this feature is a method known as "boosting." Early on in atomic weapons development, nuclear weapon scientists realized that injecting a bit of tritium gas into the center of a nuclear device could increase its destructive power tremendously. Tritium is a radioactive isotope of hydrogen, and although cosmic rays create very small quantities of tritium in the atmosphere, the only way to create usable quantities of the gas is inside nuclear reactors, by using neutron activation of lithium-6.

Nuclear boosting was first tested in 1951 in a U.S. fission bomb test codenamed "Item." The test weapon was originally a 20 kiloton device, modified to include tritium in its core. When detonated, researchers found that the boosting method increased the bomb's yield from 20 kilotons to 45.5 kilotons, more than doubling the destructive power. The amount of tritium used was only a few milliliters.

This principle was later improved upon and integrated into nuclear weapons by leaving a vacuum-sealed hollow in the center of the fissile material, and including a valve which could be opened to release tritium into the core. This allowed one weapon to offer a wide range of power, offering a small-scale "tactical" solution in the same package as a large-scale city-flattening missile... all at the twist of a knob. Eventually an electronic control was added to allow this valve to be opened remotely.

The drawback to using tritium gas in this way is that production and storage of tritium are serious problems. Tritium can only be produced inside nuclear fission reactors, so its supply is extremely limited. Moreover, its half-life is only 12.5 years, which causes tritium-boosted weapons to rapidly degrade in destructive potential while in storage. In fact some nuclear warheads cannot reach a supercritical reaction without a certain amount of radioactive tritium, which means that these weapons don't have much of a shelf-life.

Most modern nuclear weapon engineers now consider Dial-a-Yield boosting to be a design flaw due to the extreme undersupply of tritium gas, and tritium's fleeting radioactivity. But history has shown us that humans are far too clever to be outdone by nature, and soon we'll have even more efficient ways of killing lots and lots of people.

Article written by Alan Bellows, published on 25 February 2006. Alan is the founder/designer/head writer/managing editor of Damn Interesting.

Article design and artwork by Alan Bellows.
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19 Comments
Berkana
Posted 26 February 2006 at 02:31 am

In other words, they made mini H-bombs, and dialed the levels of Hydrogen (FYI for those who don't know: tritium is an isotope of hydrogen: it is hydrogen with two extra neutrons). I see.

That would certainly illustrate why there appears to be so much promise in fusion technology. Fusing a wee bit of hydrogen seems to give out a lot more energy than fissing a whole lot of uranium.


AKALucifer
Posted 26 February 2006 at 05:48 am

Ahhhh isotopes.


indra c
Posted 26 February 2006 at 12:50 pm

Alan wrote : "But history has shown us that humans are far too clever to be outdone by nature, and soon we'll have even more efficient ways of killing lots and lots of people"

...HAIL SATAN !


APA7HY
Posted 26 February 2006 at 06:39 pm

This age is gravebound.


Secret Ninja
Posted 26 February 2006 at 07:28 pm

In past generations, everyone has died.

We will just die much more gloriously.


davida
Posted 26 February 2006 at 09:17 pm

I've always been interested in "anti-nuclear" technology...you know, a missle is coming in and we blow it up with something that combines with the atoms to make...say....water or something like that. We've demonstrated we can hit a missle (ala..Patriot missles) but it would reassuring to know, we could "defuse" a nuclear weapon with chemistry. If you can't tell....I know little about science, but I also have kids, so I can continue to wish for this type of peace weapon.


Dave
Posted 27 February 2006 at 09:27 am

There are a couple of reasons why something like that won't work. One reason is that anti-missile missiles almost never explode their target. The reason is that the target is moving at many thousands of miles an hour, and, even with excellent guidance devices, it's hard to hit a beachball sized object. Heck, it'd be extremely difficult to even get the explosives to detonate at the moment of impact. By the time the explosives started exploding, the target, traveling as fast as it is, would be well past. Rather, what most of them do is either shatter the warhead with a blast wave by detonating the explosives well ahead of the projected path of the target, or, more likely, crumple part of the warhead, depending upon atmospheric friction to do the rest of the destruction (Look at what a tiny crack did to the space shuttle.).

Even if the warhead could be exploded, there isn't anything that can be done to radioactive materials to make them non-radioactive (excepting, of course, running them through a nuclear reactor or nuclear explosion, and that usually causes more problems that it solves, even if it were possible in the atmosphere). About the best that can be done is to somehow bind them into a form which won't be widely dispersed or ingested (You really, really, really don't want to ingest/inhale most radioactive materials.).

Of course, Tritium, as a radioactive element, is not exceptionally harmful, unless you happen to ingest it. In most cases, it wouldn't be a big problem to let it dissipate in the upper atmosphere (which would be a lot better than having it fuse over your house). The tricky part is that the core of the bomb is usually constructed from
Plutonium [1] [2], and having Plutonium fragments/dust rain down on your house might not be a good idea (although it may be better than having it fission over your house). Actually, the best case might be to rupture the warhead, allowing the Tritium to leak out, and allowing the core ("pit") to impact the ground (without detonating, of course), where it could be recovered relatively intact (Hey, I did say relatively, as if smashing into the ground at many thousands of miles per hour would leave it intact.). Fortunately, it takes a very precise set of explosions to cause a nuclear device to detonate, and they will not explode by merely smashing into the ground or even being set on fire [3].

[1] "Hi guys!" (I always add a friendly greeting to the NSA guys who may be reading posts which contain certain keywords that may be of interest to them.)

[2] There are actually three materials which will sustain a fission chain reaction, but I'm not going to mention the other two.

[3] For those of you with long memories, the Air Force had an accident at one of their missile silos (in Oklahoma?) where the fuel leaked out of a missle, and then exploded. This drove the 5MT (?) warhead that had been on top of the missile through a 20 ton concrete blast door, and tossed it a few miles out into the countryside. Of course, it didn't detonate.

Dave


Dave
Posted 27 February 2006 at 09:31 am

Hmm, after thinking about this for a while, I'm kind of surprised that the dial-a-yield devices use Tritium gas. I remember that was used in some of the earliest prototype weapons, but I thought that the more recent weapons had switched to Lithium-Tritide (sort of like Lithium-Hydride, except made with the Tritium isotope). Wasn't it the use of a specific isotope of Lithium that caused the Castle Bravo test shot to be MUCH stronger than predicted?

"Hi guys!"

Dave


Avenger
Posted 27 February 2006 at 11:49 am

As for anti-missile weapons, all we need to do is break apart the missile; the Vulcan Phalanx can shoot down anti-ship missiles not because of the incredible amount of depleted uranium it puts downrange, but because it puts one hole in the incoming missile. Turbulence literally breaks the missile apart after that.

Patriot missiles have been used to shoot down chemical attacks; that's actually harder in some ways than taking down a nuclear payload -- you have to handle a deadly gas, gel, or aerosol, probably by burning it out of the sky. Nukes you just have to take apart; if the weapon hasn't achieved critical mass, you just remove enough mass.


Erin1988
Posted 27 February 2006 at 08:00 pm

Wasn't Tritium what the villian in Spider-Man 2 needed?

Spider-Man 2 wasn't as good as the first. Just thought I'd throw that in.


God of Biscuits
Posted 27 February 2006 at 10:42 pm

Erin1988, open your eyes. The Spider Man movies are meant to provide you with a pscho-spiritual shock that should, if delivered effectivly, open your eyes and ears to the facist government in which we live. Also, the last Spider Man sighting occured in 1894 just outside of Westminster Abby near London. Spider Man was reported to be scaling the walls in order to perch on the rooftop of the abbey because he wanted to sit and meditate under the fig tree that the was planted high atop the tallest spire by Winston Churchill in oder to reach enlightenment. Spider Man was spotted however, and shot to death by the angry East Berlin woman's shot put team, who were visiting the abbey on a field trip sponsored by none other than our facist dictator Bill Clinton. This was indeed a sad chapter in America's history.


Erin1988
Posted 28 February 2006 at 08:57 am

God of Biscuits said: "Erin1988, open your eyes. The Spider Man movies are meant to provide you with a pscho-spiritual shock that should, if delivered effectivly, open your eyes and ears to the facist government in which we live. Also, the last Spider Man sighting occured in 1894 just outside of Westminster Abby near London. Spider Man was reported to be scaling the walls in order to perch on the rooftop of the abbey because he wanted to sit and meditate under the fig tree that the was planted high atop the tallest spire by Winston Churchill in oder to reach enlightenment. Spider Man was spotted however, and shot to death by the angry East Berlin woman's shot put team, who were visiting the abbey on a field trip sponsored by none other than our facist dictator Bill Clinton. This was indeed a sad chapter in America's history."

Well, if that isn't damn interesting...I don't know what is!

One can only hope you are able to detect sarcasm.


Glenn
Posted 11 March 2006 at 12:48 pm

Dave...

[1] "Hi guys!" (I always add a friendly greeting to the NSA guys ...

I LIKE it!

... the Air Force had an accident at one of their missile silos (in Oklahoma?) where the fuel leaked out of a missle, and then exploded. This drove the 5MT (?) warhead that had been on top of the missile through a 20 ton concrete blast door, and tossed it a few miles out into the countryside.

It was in Arkansas, 1980. The warhead was tossed "only" 600 feet away. Your number for the weight of the blast door looks correct, unlike the number in this report:

http://www.milnet.com/cdiart.htm

"Hi guys!"


pseudosanity
Posted 07 April 2006 at 10:47 am

God of Biscuits said: "Erin1988, open your eyes. The Spider Man movies are meant to provide you with a pscho-spiritual shock that should, if delivered effectivly, open your eyes and ears to the facist government in which we live. Also, the last Spider Man sighting occured in 1894 just outside of Westminster Abby near London. Spider Man was reported to be scaling the walls in order to perch on the rooftop of the abbey because he wanted to sit and meditate under the fig tree that the was planted high atop the tallest spire by Winston Churchill in oder to reach enlightenment. Spider Man was spotted however, and shot to death by the angry East Berlin woman's shot put team, who were visiting the abbey on a field trip sponsored by none other than our facist dictator Bill Clinton. This was indeed a sad chapter in America's history."

Bill Clinton was our dictator in 1894? Smoke another one you angry, angry man.


Hugh G. Rection
Posted 10 December 2006 at 04:57 am

How many tones is 100 Megatons?


ldelo
Posted 09 February 2007 at 09:39 pm

FYI, it's not really true that boosted atomic weapons are a hydrogen bomb of any sort, mini or not.

Yes, the tritium undergoes a fusion reaction or fusion-like reaction in the core during compression, but that's not what boosts the yield. The yield from the boosting agent itself is so small relative to the weapon yield that it's virtually inconsequential.

What boosting *does* do is generate a burst of high energy neutrons, which in turn trigger fast fission in the fissile material. That in turn is where the real boost comes from. I may have some of the terms or details wrong, but that's basically it.

BTW, from what I've been able to determine, the bulk of the yield in the Tsar Bomba (50 mt) came from just such fast fission.

It is generally accepted that the Tsar Bomba was basically a smaller two or three stage device (at least the physics package) with tons and tons of unenriched uranium wrapped around it. The inner device went off, and the dense pulse of high energy neutrons triggered fast fission in all that uranium. Kablooey in a very big way.

Of course the Tsar Bomba and most earlier or larger or high yield devices are basically obsoleted. The reason large bombs were developed is because of the inaccuracy of the delivery systems. At the time, the best countries with ICBM capabilities could do was to get within a distance measured in significant fractions of a mile of their target.

The delivery systems could be made larger (to carry a larger warhed) but the accuracy was limited by the technology. So, the way around that is to make the delivery system large enough to deliver a large enough warhead that even a miss of say, a kilometer, was still a kill.

But with the accuracy of modern delivery systems and the efficacy of modern weapons systems overall, the need for such large, hard to deliver, expensive to build and maintain and secure weapons is not really necessary.


dterry
Posted 21 February 2007 at 06:47 pm

How many megatons does it take to generate one jigawatt of electricity?


allduerespect88
Posted 18 December 2008 at 02:05 am

12.twenty one jigawatts!!! Of course!!!


kc-guy
Posted 14 March 2009 at 10:19 pm

♫ Para bailar Tsar Bomba! ♫

Get it? Like that La Bamba Mexican wedding song Ritchie Valens popularized in 1958...it's a...neverming


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