# Smallest (by mass) nuclear weapon **URL:** \ **Category:** Factual Questions\ **Created:** [September 12, 2012, 8:08am UTC](https://boards.straightdope.com/t/smallest-by-mass-nuclear-weapon/634481 "2012-09-12T08:08:41Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![kombatminipig](https://avatars.discourse-cdn.com/v4/letter/k/b5ac83/32.png) [@kombatminipig](https://boards.straightdope.com/u/kombatminipig)\ **Post date:** [September 12, 2012, 8:08am UTC](https://boards.straightdope.com/t/smallest-by-mass-nuclear-weapon/634481/1 "2012-09-12T08:08:41Z")
Full disclosure: this is research for a book, so no need to call the feds. Question is simple, what is the smallest feasible (by mass) thermonuclear warhead that could theoretically be constructed? The device itself can be of any size, but the main plot point is that the fissionable material needs to be light enough to be transported in a suit case. ---
**Author:** ![Der\_Trihs](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/der_trihs/32/233_2.png) [@Der\_Trihs](https://boards.straightdope.com/u/Der_Trihs)\ **Post date:** [September 12, 2012, 8:27am UTC](https://boards.straightdope.com/t/smallest-by-mass-nuclear-weapon/634481/2 "2012-09-12T08:27:28Z")
Theoretically? At one point there was talk of nuclear bullets using californium, before it became obvious each would cost billions. ---
**Author:** ![Ranchoth](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ranchoth/32/1066_2.png) [@Ranchoth](https://boards.straightdope.com/u/Ranchoth)\ **Post date:** [September 12, 2012, 8:36am UTC](https://boards.straightdope.com/t/smallest-by-mass-nuclear-weapon/634481/3 "2012-09-12T08:36:50Z")
> [@kombatminipig](#): > > Full disclosure: this is research for a book, so no need to call the feds. > > Question is simple, what is the smallest feasible (by mass) thermonuclear warhead that could theoretically be constructed? The device itself can be of any size, but the main plot point is that the fissionable material needs to be light enough to be transported in a suit case. Just a point; does it need to be a _thermonuclear_ warhead, or would a simple fission warhead suffice? And what kind of yield are you aiming for? (Also, for the record, the [W54 warhead](http://en.wikipedia.org/wiki/W54), which was actually built and used in several different weapons, had a weight of about 50 lbs., and was about 11"x5". ---
**Author:** ![Blakeyrat](https://avatars.discourse-cdn.com/v4/letter/b/ecd19e/32.png) [@Blakeyrat](https://boards.straightdope.com/u/Blakeyrat)\ **Post date:** [September 12, 2012, 6:35pm UTC](https://boards.straightdope.com/t/smallest-by-mass-nuclear-weapon/634481/4 "2012-09-12T18:35:52Z")
> [@kombatminipig](#): > > Full disclosure: this is research for a book, so no need to call the feds. > > Question is simple, what is the smallest feasible (by mass) thermonuclear warhead that could theoretically be constructed? The device itself can be of any size, but the main plot point is that the fissionable material needs to be light enough to be transported in a suit case. Critical mass of Uranium-233 is 15 kg, which is approx. an 11 cm sphere. [From wiki.](http://en.wikipedia.org/wiki/Critical_mass) 11 cm sphere would be doable in a large suitcase, but I don’t know how big all the support infrastructure needed to make it actually work would add. ---
**Author:** ![Qwertol](https://avatars.discourse-cdn.com/v4/letter/q/e274bd/32.png) [@Qwertol](https://boards.straightdope.com/u/Qwertol)\ **Post date:** [September 12, 2012, 6:41pm UTC](https://boards.straightdope.com/t/smallest-by-mass-nuclear-weapon/634481/5 "2012-09-12T18:41:59Z")
> [@Blakeyrat](#): > > Critical mass of Uranium-233 is 15 kg, which is approx. an 11 cm sphere. [From wiki.](http://en.wikipedia.org/wiki/Critical_mass) > > 11 cm sphere would be doable in a large suitcase, but I don’t know how big all the support infrastructure needed to make it actually work would add. Isn’t critical mass smaller when you are using neutron reflectors? ---
**Author:** ![Patch](https://avatars.discourse-cdn.com/v4/letter/p/a183cd/32.png) [@Patch](https://boards.straightdope.com/u/Patch)\ **Post date:** [September 12, 2012, 6:44pm UTC](https://boards.straightdope.com/t/smallest-by-mass-nuclear-weapon/634481/6 "2012-09-12T18:44:24Z")
> [@Blakeyrat](#): > > Critical mass of Uranium-233 is 15 kg, which is approx. an 11 cm sphere. [From wiki.](http://en.wikipedia.org/wiki/Critical_mass) > > 11 cm sphere would be doable in a large suitcase, but I don’t know how big all the support infrastructure needed to make it actually work would add. [The backpack nuke (or more accurately the Special Atomic Demolition Munition](http://en.wikipedia.org/wiki/Special_Atomic_Demolition_Munition)) on display at a museum in Albuquerque, New Mexico, is about the size of a large household trashcan mounted on a backpack frame. It weighed about 150 lbs. ---
**Author:** ![Gray\_Ghost](https://avatars.discourse-cdn.com/v4/letter/g/c0e974/32.png) [@Gray\_Ghost](https://boards.straightdope.com/u/Gray_Ghost)\ **Post date:** [September 12, 2012, 6:50pm UTC](https://boards.straightdope.com/t/smallest-by-mass-nuclear-weapon/634481/7 "2012-09-12T18:50:54Z")
I know I’ve cited to it before, but Cary Sublette’s [Nuclear Weapon Archive](http://nuclearweaponarchive.org/Nwfaq/Nfaq4-2.html#Nfaq4.2.2), might be of interest to you. From it, he calculates (at 4.2.3.1): > [@](#): > > Since volume increases with the cube of the radius, a thick layer of anything (explosive or reflector) surrounding the fissile core will add much more mass than that of the core itself. > > Referring to the Reflector Savings Table 4.1.7.3.2.2-3 we can see that for beryllium thicknesses of a few centimeters, the radius of a plutonium core is reduced by 40-60% of the reflector thickness. Since the density difference between these materials is on the order of 10:1, substantial mass savings can be achieved. At some point though increasing the thickness of the reflector begins to add more mass than it saves, this marks the point of minimum total mass for the reflector/core system. > > In general, minimum mass and minimum volume designs closely resemble each other. The use of a hollow core adds negligibly to the overall volume. > > The absolute minimum possible mass for a bomb is determined by the smallest critical mass that will produce a significant yield. Since the critical mass for alpha-phase plutonium is 10.5 kg, and an additional 20-25% of mass is needed to make a significant explosion, this implies 13 kg or so. A thin beryllium reflector will reduce this, but the necessary high explosive and packaging will add mass, so the true absolute minimum probably lies in the range of 10-15 kg. This is assuming you have Los Alamos to design it for you and Rocky Flats/Pantex to fabricate it for you. Parameters for a terrorist-designed weapon are covered later in the cite, and he estimates their mass at \>100 kg, 200kg for a plutonium device. EDIT: Oh, and per Ranchoth above, this is for a one stage fission weapon. Multi-stage devices aren’t dealt with. The parameters for the [W80](http://en.wikipedia.org/wiki/W80_(nuclear_warhead)) might be a good place to start. > [@](#): > > The W80 is physically quite small, the “physics package” itself is about the size of a conventional Mk.81 250 pounds (110 kg) bomb, 11.8 inches (30 cm) in diameter and 31.4 inches (80 cm) long, and only slightly heavier at about 290 pounds (130 kg). ---
**Author:** ![Tim\_T-Bonham.net](https://avatars.discourse-cdn.com/v4/letter/t/46a35a/32.png) [@Tim\_T-Bonham.net](https://boards.straightdope.com/u/Tim_T-Bonham.net)\ **Post date:** [September 12, 2012, 8:01pm UTC](https://boards.straightdope.com/t/smallest-by-mass-nuclear-weapon/634481/8 "2012-09-12T20:01:07Z")
> [@Blakeyrat](#): > > Critical mass of Uranium-233 is 15 kg, which is approx. an 11 cm sphere. [From wiki.](http://en.wikipedia.org/wiki/Critical_mass) > > 11 cm sphere would be doable in a large suitcase, but I don’t know how big all the support infrastructure needed to make it actually work would add. But what would happen when you try to carry that suitcase through the metal detector in the airport? ---
**Author:** ![Ranchoth](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ranchoth/32/1066_2.png) [@Ranchoth](https://boards.straightdope.com/u/Ranchoth)\ **Post date:** [September 13, 2012, 3:31am UTC](https://boards.straightdope.com/t/smallest-by-mass-nuclear-weapon/634481/9 "2012-09-13T03:31:28Z")
> [@t-bonham@scc.net](#): > > But what would happen when you try to carry that suitcase through the metal detector in the airport? …attach it to a nose ring, so you can sneak it past on the little tray? ---
**Author:** ![Patch](https://avatars.discourse-cdn.com/v4/letter/p/a183cd/32.png) [@Patch](https://boards.straightdope.com/u/Patch)\ **Post date:** [September 13, 2012, 5:09am UTC](https://boards.straightdope.com/t/smallest-by-mass-nuclear-weapon/634481/10 "2012-09-13T05:09:06Z")
> [@t-bonham@scc.net](#): > > But what would happen when you try to carry that suitcase through the metal detector in the airport? Tom Sizemore got one though claiming it was a garbage disposal. You might give that a try. ---
**Author:** ![MikeF](https://avatars.discourse-cdn.com/v4/letter/m/45deac/32.png) [@MikeF](https://boards.straightdope.com/u/MikeF)\ **Post date:** [September 13, 2012, 6:34pm UTC](https://boards.straightdope.com/t/smallest-by-mass-nuclear-weapon/634481/11 "2012-09-13T18:34:21Z")
The Holy Hand Grenade of Antioch was quite small but I don’t think it was nuclear. [![](https://i.ytimg.com/vi/xOrgLj9lOwk/hqdefault.jpg?sqp=-oaymwEmCOADEOgC8quKqQMa8AEB-AHeAoAC8AGKAgwIABABGGUgXyhSMA8=&rs=AOn4CLCbFWvhM8gk27b4qUoU12zCWgYlPw "Monty Python-Holy Hand Grenade") ](https://www.youtube.com/watch?v=xOrgLj9lOwk) ---
**Author:** ![billfish678](https://avatars.discourse-cdn.com/v4/letter/b/7bcc69/32.png) [@billfish678](https://boards.straightdope.com/u/billfish678)\ **Post date:** [September 13, 2012, 6:54pm UTC](https://boards.straightdope.com/t/smallest-by-mass-nuclear-weapon/634481/12 "2012-09-13T18:54:21Z")
As noted a decent neutron reflector does add significantly to the mass and volume required if you want a something like a functional nuclear weapon in the kilotons range rather than a fizzle in the hundreds of tons range. But it just occured to me you could (possibly) design a “backpack” nuke that normally wouldn’t work too well…unless you made a point of placing it a large body of water before setting it off. Pool party anyone? ---
**Author:** ![The\_Second\_Stone](https://avatars.discourse-cdn.com/v4/letter/t/bbe5ce/32.png) [@The\_Second\_Stone](https://boards.straightdope.com/u/The_Second_Stone)\ **Post date:** [September 13, 2012, 7:19pm UTC](https://boards.straightdope.com/t/smallest-by-mass-nuclear-weapon/634481/13 "2012-09-13T19:19:39Z")
> [@Der\_Trihs](#): > > Theoretically? At one point there was talk of nuclear bullets using californium, before it became obvious each would cost billions. I’ve heard Halfnium would also work similarly. ---
**Author:** ![Kevbo](https://avatars.discourse-cdn.com/v4/letter/k/e47774/32.png) [@Kevbo](https://boards.straightdope.com/u/Kevbo)\ **Post date:** [September 13, 2012, 10:26pm UTC](https://boards.straightdope.com/t/smallest-by-mass-nuclear-weapon/634481/14 "2012-09-13T22:26:02Z")
[King of the wild frontier](http://en.wikipedia.org/wiki/Davy_Crockett_(nuclear_device)) ---
**Author:** ![Bosda\_Di\_Chi\_of\_Tricor](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bosda_di_chi_of_tricor/32/16845_2.png) [@Bosda\_Di\_Chi\_of\_Tricor](https://boards.straightdope.com/u/Bosda_Di_Chi_of_Tricor)\ **Post date:** [September 13, 2012, 10:52pm UTC](https://boards.straightdope.com/t/smallest-by-mass-nuclear-weapon/634481/15 "2012-09-13T22:52:21Z")
> [@Kevbo](#): > > [King of the wild frontier](http://en.wikipedia.org/wiki/Davy_Crockett_(nuclear_device)) I _knew_ that would come up. How did we ever get that crazy?:eek::dubious: ---
**Author:** ![Gray\_Ghost](https://avatars.discourse-cdn.com/v4/letter/g/c0e974/32.png) [@Gray\_Ghost](https://boards.straightdope.com/u/Gray_Ghost)\ **Post date:** [September 13, 2012, 11:30pm UTC](https://boards.straightdope.com/t/smallest-by-mass-nuclear-weapon/634481/16 "2012-09-13T23:30:31Z")
> [@Bosda\_Di\_Chi\_of\_Tricor](#): > > I _knew_ that would come up. > > How did we ever get that crazy? Being outnumbered 5-1 + in tanks tends to make one come up with unusual solutions. Like the [neutron bomb](http://www.globalsecurity.org/wmd/intro/neutron-bomb.htm). The W-54 that Ranchoth mentioned up above, is the warhead at the heart of the Davy. As well as the SADM. I think it’s amazing that we haven’t been able to improve on its size in 50 years. So far as you and I know. I guess the old Soviet ‘nuclear briefcases’ that [Alexander Lebed](http://nuclearweaponarchive.org/News/Lebedbomb.html) and Stanislav Lunev went on and on about, [may have been smaller.](http://cns.miis.edu/stories/020923.htm), though probably not as small as that mockup that Rep. Curt Weldon was holding up. I can’t stop laughing, looking at the pictures of the Davy Crockett. It looks like something right out of the _[Fallout](http://fallout.wikia.com/wiki/Fallout_Wiki)_ series, like it should be on the cover of a Tom Swift book. I guess they [test-fired it](http://en.wikipedia.org/wiki/Little_Feller_(nuclear_tests)) at the end of U.S. atmospheric testing and it worked. You couldn’t get me within 10 miles of that thing launching. ---
**Author:** ![Big\_G](https://avatars.discourse-cdn.com/v4/letter/b/a88e4f/32.png) [@Big\_G](https://boards.straightdope.com/u/Big_G)\ **Post date:** [September 14, 2012, 4:47pm UTC](https://boards.straightdope.com/t/smallest-by-mass-nuclear-weapon/634481/17 "2012-09-14T16:47:13Z")
I happen to be reading “Project Orion” by George Dyson, about the development of a nuclear bomb powered spaceship in the 50’s and 60’s. One of the people involved was Ted Taylor, who had spent time at Los Alamos trying to see how large and small you can make fission bombs. In Chapter 6, he is quoted as saying “I was narrowing my focus, getting the quantities of plutonium that one could use to make nuclear explosions, down into less than a kilogram. Quite a bit less.” He also talks about a “…full implosion bomb that you could hold in one hand that was about six inches in diameter.” ---
**Author:** ![Big\_G](https://avatars.discourse-cdn.com/v4/letter/b/a88e4f/32.png) [@Big\_G](https://boards.straightdope.com/u/Big_G)\ **Post date:** [September 14, 2012, 5:01pm UTC](https://boards.straightdope.com/t/smallest-by-mass-nuclear-weapon/634481/18 "2012-09-14T17:01:13Z")
I got ahead of myself and posted before I read the whole thread, but I missed the edit window to add this: The beginning the the second quote from Ted Taylor that I excerpted above references the Davy that **Kevbo** brought up. ““I tried to find out what was the smallest bomb you could produce, and it was a lot smaller than Davy Crockett, but it was never built in those years,” says Ted. “But it certainly has been since then.”” (“Project Orion” by George Dyson, pg 55) ---
**Author:** ![billfish678](https://avatars.discourse-cdn.com/v4/letter/b/7bcc69/32.png) [@billfish678](https://boards.straightdope.com/u/billfish678)\ **Post date:** [September 14, 2012, 5:09pm UTC](https://boards.straightdope.com/t/smallest-by-mass-nuclear-weapon/634481/19 "2012-09-14T17:09:49Z")
> [@Big\_G](#): > > He also talks about a “…full implosion bomb that you could hold in one hand that was about six inches in diameter.” Oh, you can probably make a nuclear device pretty damn small. It just depends on what you want to call a “nuclear weapon”. A 10 kiloton blast yeild. Nuclear Weapon for sure. 1 kiloton? A 100 ton? One ton? A hundred pounds? Ten pounds? Note that for an Orion like project,even a crappy bomb that weighed, oh lets say 20 pounds, but had a one ton yield, would be vast improvement when it came propulsive efficiency over even the best chemical rockets. Thats roughly a hundred times more energy per mass. ---
**Author:** ![Gray\_Ghost](https://avatars.discourse-cdn.com/v4/letter/g/c0e974/32.png) [@Gray\_Ghost](https://boards.straightdope.com/u/Gray_Ghost)\ **Post date:** [September 14, 2012, 6:01pm UTC](https://boards.straightdope.com/t/smallest-by-mass-nuclear-weapon/634481/20 "2012-09-14T18:01:45Z")
> [@Big\_G](#): > > ..One of the people involved was Ted Taylor, who had spent time at Los Alamos trying to see how large and small you can make fission bombs. In Chapter 6, he is quoted as saying “I was narrowing my focus, getting the quantities of plutonium that one could use to make nuclear explosions, down into less than a kilogram. Quite a bit less.” He also talks about a “…full implosion bomb that you could hold in one hand that was about six inches in diameter.”… > > ““I tried to find out what was the smallest bomb you could produce, and it was a lot smaller than Davy Crockett, but it was never built in those years,” says Ted. “But it certainly has been since then.”” (“Project Orion” by George Dyson, pg 55) The [W48](http://en.wikipedia.org/wiki/W48), used in the 152 and 155mm nuclear artillery shells, was about the diameter you cite. Interestingly, the wiki for the W48 mentions a quote from Dr. Taylor that 105 mm nuclear artillery shells were possible. He certainly had style; I don’t know of any other man who [lit his cigarette from a nuclear explosion.](http://gpsinertial.blogspot.com/2010/09/how-to-light-cigarette-safely-with.html) Browsing around, I have seen figures for Pu-239 critical masses that were on the order of a kilogram. They required dissolution in water, and were the bottom of the extrapolated curves of critical mass, but that’s still quite a bit smaller than the 10.5 kg Sublette cites for the critical mass of a bare alpha-phase sphere in air. More exotic configurations have been proposed and experimented with, including the layering of thin foils of Pu-239 atop thicker slabs of D2O and then dunking the whole thing in liquid helium. Evidently, the critical mass for Pu-239 can get down into the sub-ounce range in such experiments. I wonder if, since water is such an effective moderator, and an effective moderator helps improve the likelihood of a neutron fissioning an actinide nucleus, how effective would ice be in a device design? If you dissolved Pu into water, and froze the lot, would that lower the required amount of Pu? I’m sure I’m missing something fundamental here. [Next page](https://boards.straightdope.com/t/smallest-by-mass-nuclear-weapon/634481.md?page=2)