# What is the least powerful fission explosion possible? **URL:** \ **Category:** Factual Questions\ **Created:** [March 2, 2012, 10:19pm UTC](https://boards.straightdope.com/t/what-is-the-least-powerful-fission-explosion-possible/614592 "2012-03-02T22:19:28Z")\ **Posts on this page:** 19\ **Page:** 1
**Author:** ![Christopher\_Robin\_Davies](https://avatars.discourse-cdn.com/v4/letter/c/8dc957/32.png) [@Christopher\_Robin\_Davies](https://boards.straightdope.com/u/Christopher_Robin_Davies)\ **Post date:** [March 2, 2012, 10:19pm UTC](https://boards.straightdope.com/t/what-is-the-least-powerful-fission-explosion-possible/614592/1 "2012-03-02T22:19:28Z")
I know there is a concept in nuclear weapons called critical mass in which a certain amount of weapons-grade fissionable material is needed for a nuclear explosion. I know that such explosions are measured in terms of kilotons (or megatons) of TNT.l I do not know what is the smallest such explosion possible, and that is the question I am asking today. Thank you. ---
**Author:** ![Alka\_Seltzer](https://avatars.discourse-cdn.com/v4/letter/a/c89c15/32.png) [@Alka\_Seltzer](https://boards.straightdope.com/u/Alka_Seltzer)\ **Post date:** [March 2, 2012, 10:31pm UTC](https://boards.straightdope.com/t/what-is-the-least-powerful-fission-explosion-possible/614592/2 "2012-03-02T22:31:42Z")
According to the [Davy Crocke](http://en.wikipedia.org/wiki/Davy_Crockett_(nuclear_device))t article, the yield of that weapon was between 10 or 20 tons of TNT (0.01-0.02 kilotons). It says this is near the minimum practical yield for a fission weapon. ---
**Author:** ![Koxinga](https://avatars.discourse-cdn.com/v4/letter/k/4af34b/32.png) [@Koxinga](https://boards.straightdope.com/u/Koxinga)\ **Post date:** [March 2, 2012, 10:39pm UTC](https://boards.straightdope.com/t/what-is-the-least-powerful-fission-explosion-possible/614592/3 "2012-03-02T22:39:59Z")
Would that overlap with any of the strongest possible conventional explosives? Apologies for not checking out Wikipedia as I’m on mobile. ---
**Author:** ![Fear\_Itself](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/fear_itself/32/19637_2.png) [@Fear\_Itself](https://boards.straightdope.com/u/Fear_Itself)\ **Post date:** [March 2, 2012, 10:46pm UTC](https://boards.straightdope.com/t/what-is-the-least-powerful-fission-explosion-possible/614592/4 "2012-03-02T22:46:02Z")
> [@Koxinga](#): > > Would that overlap with any of the strongest possible conventional explosives? Apologies for not checking out Wikipedia as I’m on mobile. > **[Largest artificial non-nuclear explosions](https://en.wikipedia.org/wiki/List_of_the_largest_artificial_non-nuclear_explosions#Comparison_with_large_conventional_military_ordnance)** > > There have been many extremely large explosions, accidental and intentional, caused by modern high explosives, boiling liquid expanding vapour explosions (BLEVEs), older explosives such as gunpowder, volatile petroleum-based fuels such as petrol, and other chemical reactions. This list contains the largest known examples, sorted by date. An unambiguous ranking in order of severity is not possible; a 1994 study by historian Jay White of 130 large explosions suggested that they need to be ranked... > [@](#): > > The most powerful non-nuclear weapons ever designed are the United States’ [MOAB](http://en.wikipedia.org/wiki/MOAB) (standing for _Massive Ordnance Air Blast_, also nicknamed _Mother Of All Bombs_, tested in 2003) and the Russian [Father of All Bombs](http://en.wikipedia.org/wiki/Father_of_All_Bombs) (tested in 2007). The MOAB contains 18,700 lb (8.5 t) of the H6 explosive, which is 1.35 times as powerful as TNT, giving the bomb an approximate yield of 0.011 kt. The FOAB is about 4 times more powerful than the MOAB. ---
**Author:** ![md2000](https://avatars.discourse-cdn.com/v4/letter/m/73ab20/32.png) [@md2000](https://boards.straightdope.com/u/md2000)\ **Post date:** [March 2, 2012, 10:50pm UTC](https://boards.straightdope.com/t/what-is-the-least-powerful-fission-explosion-possible/614592/5 "2012-03-02T22:50:36Z")
I think it was uois SLotlin who killed himself with a screwdriver and a bunch of fission material. The theory is that it could have been a lot worse if he hadn’t acted quickly. > **[Louis Slotin](https://en.wikipedia.org/wiki/Louis_Slotin)** > > Louis Alexander Slotin (1 December 1910 – 30 May 1946) was a Canadian physicist and chemist who took part in the Manhattan Project. Born and raised in the North End of Winnipeg, Manitoba, Slotin earned both his Bachelor of Science and Master of Science degrees from the University of Manitoba, before obtaining his doctorate in physical chemistry at King's College London in 1936. Afterwards, he joined the University of Chicago as a research associate to help design a cyclotron. > In 1942, Slotin w... In _Sum of All Fears_ (the book, not the movie) by Tom Clancy, the author posits a poorly constructed A-bomb that fizzles, barely killing anyone beyond the confines of the Superbowl Stadium. A chain reaction happens when a critical mass of fissionable material is brought together. What constitutes a critical mass and how long it takes depends on a number of factors - the purity of the material (different isotopes are more or less susceptible to splitting and releasing energy and other particles) and how long the the mass stays together, considering part of the result of the release of a massive amount of heat in a short time is, of course, explosion. The fizzle in \*SoAF \* is a result of the fission material dispersing before enough neutrons were released and able to split enough fissible material. The first nuclear test by North Korea was also reported by some to have fizzled and failed to produce even a kiloton explosion. [2006 North Korean nuclear test - Wikipedia](http://en.wikipedia.org/wiki/2006_North_Korean_nuclear_test) versus 12 to 20KT for the first American bombs. So it depends… ---
**Author:** ![md2000](https://avatars.discourse-cdn.com/v4/letter/m/73ab20/32.png) [@md2000](https://boards.straightdope.com/u/md2000)\ **Post date:** [March 2, 2012, 10:55pm UTC](https://boards.straightdope.com/t/what-is-the-least-powerful-fission-explosion-possible/614592/6 "2012-03-02T22:55:07Z")
The Americans also had designs for artillery-based battelefield nukes, which presumably would be fairly low yield… Pls, the neutron bomb design was basically a nuke that fizzles, producing a flood of lethal neutrons rather than a large heat-and-shockwave explosion. The lethal effects would be felt for a longer distance, while the explosion would not be much more than a large conventional bomb. [Neutron bomb - Wikipedia](http://en.wikipedia.org/wiki/Neutron_bomb) - however, this article says the explosion would still be a kiloton range. ---
**Author:** ![Francis\_Vaughan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/francis_vaughan/32/3093_2.png) [@Francis\_Vaughan](https://boards.straightdope.com/u/Francis_Vaughan)\ **Post date:** [March 2, 2012, 11:38pm UTC](https://boards.straightdope.com/t/what-is-the-least-powerful-fission-explosion-possible/614592/7 "2012-03-02T23:38:27Z")
The problem with any device is self disassembly - once you reach critical mass the lump of fissile material will blow itself apart stopping the reaction. That is essentially what happened in the Slotin accident. The yield is so low that a fire cracker probably makes more noise. A weapon tries to maximise the yield with a whole range of techniques, the main one being explosive containment - where there is a conventional explosive whose job is to compress and contain the fissile mass for long enough that the reaction can proceed far enough to get a useful yield. The longer the better. The better you do this the higher the yield, and conversely the worse you do this the lower the yield all the way down to a device that does little more than blow itself apart. Because the reaction is exponential the time contained makes a huge difference. You could probably come up with a theoretical minimum yield based upon no confinement and a minimum fissile (i.e. just critical) mass so that only the inertia of the material is involved in keeping it together. As Slotin found, the neutron flux will kill you, but the explosive yield is essentially zero. ---
**Author:** ![dzero](https://avatars.discourse-cdn.com/v4/letter/d/5f9b8f/32.png) [@dzero](https://boards.straightdope.com/u/dzero)\ **Post date:** [March 3, 2012, 1:23am UTC](https://boards.straightdope.com/t/what-is-the-least-powerful-fission-explosion-possible/614592/8 "2012-03-03T01:23:30Z")
It seems that post #2 answered the question, but this might be interesting - [Regular or Extra Crispy.](http://www.damninteresting.com/dial-a-yield-nukes-regular-or-extra-crispy/) > [@](#): > > 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. ---
**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:** [March 3, 2012, 1:29am UTC](https://boards.straightdope.com/t/what-is-the-least-powerful-fission-explosion-possible/614592/9 "2012-03-03T01:29:19Z")
If by “smallest possible” you mean _theoretically_ possible instead of _practically_ possible, in theory you can make very small nuclear weapons using californium; before people realized just how impractical it is to make it in significant amounts there was speculation about nuclear bullets using californium for the warheads. ---
**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:** [March 3, 2012, 2:17am UTC](https://boards.straightdope.com/t/what-is-the-least-powerful-fission-explosion-possible/614592/10 "2012-03-03T02:17:30Z")
[More grist for the mill](http://nuclearweaponarchive.org/Nwfaq/Nfaq4-2.html#Nfaq4.2.3). The nuclear weapon archive is a useful starting point for many questions on the design and effects of these weapons. I hope the following relevant quote from it is small enough to fall under fair use: > [@](#): > > 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. > > The W54 warhead used in the Davy Crockett had a minimum mass of about 23 kg, and had yields ranging from 10 tons up to 1 kt in various mods (probably achieved by varying the fissile content). The warhead was basically egg-shaped with the minor axis of 27.3 cm and a major axis of 40 cm. The W-54 probably represents a near minimum diameter for a spherical implosion device (the U.S. has conducted tests of a 25.4 cm implosion system however). > > The test devices for this design fired in Hardtack Phase II (shots Hamilton and Humboldt on 15 October and 29 October 1958) weighed only 16 kg, impressively close to the minimum mass estimated above. These devices were 28 cm by 30 cm, Humboldt used PBX-9404 as the explosive. > > 4.2.3.2 Minimum Fissile Content > > The contrasting approach to minimizing size is to make a small explosion in the most efficient way as possible. This means applying the same principles as high efficiency design, but simply reducing the amount of fissile material to reduce the yield. The mass of the implosion system, and the tamper/reflector in this case will result in greater overall mass and volume, even though the fissile material weight is reduced. > > Using an advanced flying plate design it is possible to compress a 1 kg plutonium mass sufficiently to produce a yield in the 100 ton range. This design has an important implication on the type of fissile material that can be used. The high compression implies fast insertion times, while the low mass implies a low Pu-240 content. Taken together this means that a much higher Pu-240 content than normal weapon grade plutonium could be used in this type of design without affecting performance. In fact ordinary reactor grade plutonium would be as effective as weapon grade material for this use. Fusion boosting could produce yields exceeding 1 kt with this system. ---
**Author:** ![bump](https://avatars.discourse-cdn.com/v4/letter/b/7c8e57/32.png) [@bump](https://boards.straightdope.com/u/bump)\ **Post date:** [March 3, 2012, 5:02pm UTC](https://boards.straightdope.com/t/what-is-the-least-powerful-fission-explosion-possible/614592/11 "2012-03-03T17:02:09Z")
> [@md2000](#): > > The Americans also had designs for artillery-based battelefield nukes, which presumably would be fairly low yield… Pls, the neutron bomb design was basically a nuke that fizzles, producing a flood of lethal neutrons rather than a large heat-and-shockwave explosion. The lethal effects would be felt for a longer distance, while the explosion would not be much more than a large conventional bomb. [Neutron bomb - Wikipedia](http://en.wikipedia.org/wiki/Neutron_bomb) - however, this article says the explosion would still be a kiloton range. It’s more of a bastardized fusion weapon that fuses tritium, IIRC, with the intention of creating an intense burst of radiation, but very little yield from the fusion reactions. In other words, the fission trigger works as usual, but the fusion stage is tritium instead of lithium deuteride, which changes the characteristics of the reaction dramatically. Nuclear weapon design is a series of tradeoffs- are the designers aiming for minimum fissile content, minimum weapon size, or something else like minimum yield? Each approach is different- minimum size weapons are frequently not very efficient, and minimum fissile content weapons are by nature, efficient, but can be larger and heavier for the same yield vs. a less efficient warhead of the same yield. 10-20 tons is like other posters have said, near the minimum realistic yield for fission weapons using the normal HEU and plutonium. ---
**Author:** ![si\_blakely](https://avatars.discourse-cdn.com/v4/letter/s/d9b06d/32.png) [@si\_blakely](https://boards.straightdope.com/u/si_blakely)\ **Post date:** [March 4, 2012, 7:59am UTC](https://boards.straightdope.com/t/what-is-the-least-powerful-fission-explosion-possible/614592/12 "2012-03-04T07:59:53Z")
> [@md2000](#): > > In _Sum of All Fears_ (the book, not the movie) by Tom Clancy, the author posits a poorly constructed A-bomb that fizzles, barely killing anyone beyond the confines of the Superbowl Stadium. The weapon was a boosted fission device - the plutonium pit includes a small amount of tritium for a low level of fusion that increases the number of neutrons, improving fission. This tritium needs refreshing, as tritium decay produces Helium-3 that will absorb neutrons. The terrorists kill the nuclear engineer (East German) who designed the bomb and who had withheld this bit of information in an effort to stay alive - he just hadn’t mentioned that an additional step needed to be taken before deployment. Si ---
**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:** [March 4, 2012, 12:42pm UTC](https://boards.straightdope.com/t/what-is-the-least-powerful-fission-explosion-possible/614592/13 "2012-03-04T12:42:02Z")
> [@Alka\_Seltzer](#): > > According to the [Davy Crocke](http://en.wikipedia.org/wiki/Davy_Crockett_(nuclear_device))t article, the yield of that weapon was between 10 or 20 tons of TNT (0.01-0.02 kilotons). It says this is near the minimum practical yield for a fission weapon. “King Of The Wild Frontier” _indeed!_:eek: ---
**Author:** ![Christopher\_Robin\_Davies](https://avatars.discourse-cdn.com/v4/letter/c/8dc957/32.png) [@Christopher\_Robin\_Davies](https://boards.straightdope.com/u/Christopher_Robin_Davies)\ **Post date:** [March 4, 2012, 7:10pm UTC](https://boards.straightdope.com/t/what-is-the-least-powerful-fission-explosion-possible/614592/14 "2012-03-04T19:10:41Z")
> [@Der\_Trihs](#): > > If by “smallest possible” you mean _theoretically_ possible instead of _practically_ possible, in theory you can make very small nuclear weapons using californium; before people realized just how impractical it is to make it in significant amounts there was speculation about nuclear bullets using californium for the warheads. Thank you, theoretically possibleis just what I meant I am sorry I was not clearer. What is the smallest explosion youcould get with californium. ---
**Author:** ![sweeteviljesus](https://avatars.discourse-cdn.com/v4/letter/s/898d66/32.png) [@sweeteviljesus](https://boards.straightdope.com/u/sweeteviljesus)\ **Post date:** [March 13, 2012, 8:35pm UTC](https://boards.straightdope.com/t/what-is-the-least-powerful-fission-explosion-possible/614592/15 "2012-03-13T20:35:56Z")
> [@si\_blakely](#): > > The weapon was a boosted fission device - the plutonium pit includes a small amount of tritium for a low level of fusion that increases the number of neutrons, improving fission. This tritium needs refreshing, as tritium decay produces Helium-3 that will absorb neutrons. The terrorists kill the nuclear engineer (East German) who designed the bomb and who had withheld this bit of information in an effort to stay alive - he just hadn’t mentioned that an additional step needed to be taken before deployment. > > Si It was supposed to be a 400kt device that fizzled with a yield of 11kt. 400kt seems awfully high for a boosted fission weapon. ---
**Author:** ![alysdexia](https://avatars.discourse-cdn.com/v4/letter/a/e9a140/32.png) [@alysdexia](https://boards.straightdope.com/u/alysdexia)\ **Post date:** [October 1, 2015, 1:47pm UTC](https://boards.straightdope.com/t/what-is-the-least-powerful-fission-explosion-possible/614592/16 "2015-10-01T13:47:52Z")
> [@Alka\_Seltzer](#): > > According to the [Davy Crocke](http://en.wikipedia.org/wiki/Davy_Crockett_(nuclear_device))t article, the yield of that weapon was between 10 or 20 tons of TNT (0.01-0.02 kilotons). It says this is near the minimum practical yield for a fission weapon. The threshold between fizzle and shock should lie between the 1.2 t and 7.8 t of the Hamilton and Humboldt tests: > **[Operation Hardtack II](https://en.wikipedia.org/wiki/Operation_Hardtack_II)** > > Download coordinates as: > Operation Hardtack II was a series of 37 nuclear tests conducted by the United States in 1958 at the Nevada Test Site. These tests followed the Operation Argus series and preceded the Operation Nougat series. > With test moratoriums on the horizon, American weapons labs rushed out many new designs. A hard deadline for testing was set at midnight (0000 hrs), October 31, 1958, as negotiations were set to start that day, and the schedule shows it, with 29 tests executed in... [http://nuclearweaponarchive.org/Usa/Tests/Hardtack2.html](http://nuclearweaponarchive.org/Usa/Tests/Hardtack2.html) ---
**Author:** ![Hail\_Ants](https://avatars.discourse-cdn.com/v4/letter/h/dc4da7/32.png) [@Hail\_Ants](https://boards.straightdope.com/u/Hail_Ants)\ **Post date:** [October 2, 2015, 12:09am UTC](https://boards.straightdope.com/t/what-is-the-least-powerful-fission-explosion-possible/614592/17 "2015-10-02T00:09:01Z")
> [@sweeteviljesus](#): > > It was supposed to be a 400kt device that fizzled with a yield of 11kt. 400kt seems awfully high for a boosted fission weapon. It was supposed to be a true three stage fission-fusion-fission H-bomb (and I thought the predicted yield was higher than 400kt). I remember in the book after the bomb goes off an American military scientist first on the scene takes a sample of fallout, puts it into an analyzing machine of some kind and says, \*“Whoa! Look at that Tritium count! This was a three-stager!” - For those who haven’t read the book: A key plot point after the bomb goes off is even though the reader is told the bomb fizzled (Clancy gives an awesome nanosecond-by-nanosecond description in the chapter _Three Shakes_) the US is still fooled into believing it was a larger detonation and therefore a Russian attack not a terrorists one. It’s finally figured out that the miscalculation was because when the enormous asphalt parking lot at the stadium was vaporized it made the yield look much larger to the satellites that first detect the detonation. ---
**Author:** ![CalMeacham](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/calmeacham/32/35_2.png) [@CalMeacham](https://boards.straightdope.com/u/CalMeacham)\ **Post date:** [October 2, 2015, 11:18am UTC](https://boards.straightdope.com/t/what-is-the-least-powerful-fission-explosion-possible/614592/18 "2015-10-02T11:18:45Z")
The disaster at Kyshtim/Chelyabinsk in the former Soviet Union was due to an explosion due to improperly cooled nuclear waste. It wasn’t a “fission explosion”, but it certainly was due to the heat generated by fission decay (although not a chain reaction). The explosion was estimated to be the equivalent of 70-100 tons of TNT. > **[Kyshtym disaster](https://en.wikipedia.org/wiki/Kyshtym_disaster)** > > The Kyshtym disaster, sometimes referred to as the Mayak disaster or Ozyorsk disaster in newer sources, was a radioactive contamination accident that occurred on 29 September 1957 at Mayak, a plutonium production site for nuclear weapons and nuclear fuel reprocessing plant located in the closed city of Chelyabinsk-40 (now Ozyorsk) in Chelyabinsk Oblast, Russian SFSR, Soviet Union. > The disaster is the second-worst nuclear incident by radioactivity released, after the Chernobyl disaster. It is t... The area ended up being dangerously radioactive, and still is (two other incidents also contributed to the radioactivity). Zhores Medvedev mentioned the situation in the 1970s, and was immediately accused of being an alarmist. But the incident, while well-known in Russia, was virtually unheard-of in the West. (The CIA knew about it, but the government clamped a lid down on disclosures, maybe not wanting to have people freaking out about nuclear power) So he put together a book, **Nuclear Disaster in the Urals** , in which he proved that some sort of event occurred there in 1957 from available news and journal reports. There are some folks who say that we narrowly avoided a similar disaster at the storage facility in Hanford, Washington. ---
**Author:** ![gnoitall](https://avatars.discourse-cdn.com/v4/letter/g/bb73d2/32.png) [@gnoitall](https://boards.straightdope.com/u/gnoitall)\ **Post date:** [October 2, 2015, 2:31pm UTC](https://boards.straightdope.com/t/what-is-the-least-powerful-fission-explosion-possible/614592/19 "2015-10-02T14:31:31Z")
> [@CalMeacham](#): > > The disaster at Kyshtim/Chelyabinsk in the former Soviet Union was due to an explosion due to improperly cooled nuclear waste. It wasn’t a “fission explosion”, but it certainly was due to the heat generated by fission decay (although not a chain reaction). The explosion was estimated to be the equivalent of 70-100 tons of TNT. > > [Kyshtym disaster - Wikipedia](https://en.wikipedia.org/wiki/Kyshtym_disaster) I doubt this case is germane to this question, since the explosion itself wasn’t nuclear in any sense. It was a chemical explosion caused by concentrated solvent, which happened to contain dissolved radioactive metals. The same solvents in the same concentrations, heated to the same temperature by any other means, would have exploded identically. This case is more like a hypothetical “dirty bomb”: conventional explosive seeded with radioactive compounds to generate a plume of radioactive fallout dispersed by a normal chemical explosion.