Nuclear Weapons and Radiation - Misc Facts

This page holds a few misc. facts about nuclear weapons and radiation that may be surprising to many.

Suitcase Nukes | Weapons Engineering  | Radiation Facts | Nuclear Blast Effects | Historic Radiation Releases
Nuclear Physics Reference | References

Current Affairs Essays by John Moore (my blog) | Other Essays

Terrorist Related Information ("Suitcase Nukes")


The US produced, and for many years deployed "Atomic Demolition Munitions." The Medium Atomic Demolition Munition (MADM) produced 1-15 kilotons of yield, and weighed 400 pounds. The Special Atomic Demolition Munition (SADM)  yielded .01-1 kilotons and weighed only 163 pounds.  


The smallest nuclear weapon the US produced was the "Davy Crockett"  - a recoilless rifle round. It weighed about 51 pounds, was 16 inches long and 11 inches in diameter. It produced a variable yield of up to 1 kiloton.


An excellent discussion of this issue is here.


The Soviets supposedly produced "suitcase nukes" and there is no reason to doubt this assertion. Former Soviet General Ledbed has asserted that a number of these are not accounted for. There are reasons, however, to doubt his assertions given his political position. Interestingly, Ledbed was recently killed in a helicopter crash.


The Soviets supposedly produced "suitcase nukes" and there is a US DOE estimate that only 4kg of Plutonium is necessary to make a fission weapon. Some believe that only 1kg is needed.


North Korea's weapon's program is using an implosion design with Plutonium. This design may eventually lead to concealable nuclear weapons, which might be sold to terrorists or terrorist supporting countries for anonymous nuclear attacks.


Basic Nuclear Weapons Engineering

See Nuclear Weapons FAQ for primary reference material.


All known nuclear weapons require the fission of Uranium (235 or 233) or Plutonium 239. An "atomic bomb" (fission weapon) uses the fission energy directly, while a "hydrogen bomb" (thermonuclear weapon) uses fission to ignite a fusion reaction, achieving much higher energy release. In theory, there is no limit to the power of a fusion bomb. There has been speculation that it is possible to create useful fusion weapons without a uranium trigger, but no reliable unclassified information indicates that this is true, and there is a difficult physical principle to overcome.


Uranium consisting of unnaturally high amounts of isotopes 233 and 235 is called enriched uranium. Uranium is a common element on earth, but U-233 and U-235 constitute small percentages of it (<1%) and are always found mixed with the less useful U-238.


Fission is the process whereby an atom's nucleus splits, releasing a large amount of energy. In a simple fission weapon, fission occurs when a neutron is absorbed by a nucleus, causing it to be highly unstable, at which point the nucleus splits, releasing a large amount of energy and more neutrons. This only occurs easily in a few  isotopes (in Uranium, 235 or 233).


A chain reaction occurs because the fission of a nucleus releases additional neutrons, which can then cause fission in more nuclei.


Critical mass is the amount of fissile material needed for a chain reaction to become self-sustaining. This means that for each neutron released in the material, on average one more neutron will be released as a result. The critical mass is a factor not just of the type and amount of material, but also its instantaneous density and geometry. In other words, a mass of plutonium might not be critical until it is rapidly and highly compressed by high velocity  "implosion."


Fission weapons explode when the fissile material is suddenly placed in a configuration significantly greater than the critical mass - a state of supercriticality. If critical mass is reached too slowly, the weapon will explode with greatly reduced energy, possibly simply melting.


When a weapon has reached supercriticality, it still may not explode unless a neutron passes into the core. Since a high explosive implosion maintains criticality for only a few microseconds, a neutron flux generator may be required to guarantee this.


The easiest weapon to build uses a large amount (tens of kilograms) of enriched uranium. Because uranium releases neutrons at a very low rate, the weapon can use a relatively long "assembly time" to reach supercriticality. One design uses a sphere with a cylindrical hole in it, and a "gun" to fire a cylinder of uranium into that hole. Until the cylinder is inserted, both assemblies are well below critical mass, but when the cylinder is inserted, the mass rapidly rises to supercriticality. A neutron randomly released by the material during this process triggers the chain reaction. This weapon is so simple that the US used one against Nagasaki without ever testing the design. These weapons tend to be fairly large and inefficient, although the design was used in a US nuclear artillery shell.


A plutonium based weapon cannot use the "gun" approach, because plutonium releases too many neutrons, which would cause the chain reaction to start long before the mass was supercritical enough to cause a large explosion. Hence plutonium weapons require assembly by compressing a sphere or shell of plutonium very rapidly, using high velocity explosives. This neccessitates very high quality explosives, a very precise machining of all parts, and an electrical detonating system which can deliver very high energy pulses to a number of detonators with great timing precision. Hence plutonium based weapons are significantly harder to build. The US tested one at Trinity Site before deploying another against Nagasaki.


A uranium weapon can also use the implosion approach, to achieve greater efficiency. However, in this case it requires a neutron flux generator to assure that enough neutrons flood the core during the maximal period of compression that the chain reaction will start and the weapon will be efficient.


Uranium weapons require the production of enriched uranium (although it does not have to be as highly enriched as is used in some power reactors). This is a complex process because it requires the separation of isotopes of the same element (which means they have the same chemical behavior) and the isotopes have almost the same weight. Thus multiple stages of gas diffusion, centrifuges or electromagnetic (calutron) separation are required. This is inevitably a major industrial project, and is likely to be detectable by intelligence agencies. However, the centrifuge method can be  distributed, making it hard to spot. It is believed that Saddam Hussein intended to use this approach once he was rid of UN inspectors. Laser separation has also been used. In addition, there may be new technologies that make enrichment much easier to do or at least easier to conceal. Only a ton or so of natural uranium is required to produce enough entriched uranium for a weapon.


Plutonium weapons require the production of highly pure plutonium. Because plutonium is a not found in nature, it must be made in a nuclear reactor. Once made, however, it is relatively easy to extract because it is chemically different from the other elements in the mix, although the extraction process must take place in an environment made extremely radioactive by other elements mixed with the plutonium.


Fusion weapons can be  much more powerful than fission weapons, but require a subtle and difficult design. However, at least two different teams (Teller-Ulam and Sakarov) independently discovered the same approach. Since that time knowledge of fusion designs has spread through espionage and possibly technology trades. The details of fusion weapons will not be discussed here - see the Nuclear Weapons FAQ for vastly more information.

Radiation Risk - The Facts, not the Scare Stories

bulletMyth: Nuclear war would end human life on earth through radiation. Fact:If all of the nuclear weapons in stock at the height of the cold war were detonated, the average radiation dose per person is only 1/100th of a lethal dose, and well below doses which can be shown to have even long term effects (such as cancer).
bulletMyth: Chernobyl caused or will cause thousands of deaths. Fact:The Chernobyl disaster was the worst possible reactor disaster. It released an extremely large amount of radiation into the environment (see below). Even so, there have been no detectable increases in death rates even among the most highly exposed population (other than those who received extremely high doses fighting the fire, and many of whom died as a result). The radiation levels of the "highly radioactive" regions evacuated after the event are significantly lower than the natural radiation level in many parts of the world. Long term very sensitive genetic studies of animals in the most highly exposed region have found no abnormalities. There is no excess of three eared rabbits or 10 pound cockroaches around Chernobyl!
bulletMyth:Fallout caused deaths in Japanese nuclear bombings. Fact:There was no significant fallout in the vicinity of the Hiroshima and Nagasaki bombings. All radiation injuries were a result of immediate (first 1 minute) radiation.
bulletThe United States Transuranium and Uranium Registries (USTUR), operated by Washington State University, reports: "The health effects from plutonium, americium, and uranium intakes by humans, as determined with USTUR data can be summarized in two words, virtually none.  A study of the causes of death of USTUR organ donors has been completed.  The study showed that the vast majority of USTUR donors died from the same diseases that have caused the deaths of most of the U. S. population, heart disease, strokes, and cancers not necessarily associated with radiation exposure.  This is in spite of the fact that the USTUR donors are a biased population in that a number of donors volunteered for the program after having been diagnosed with cancer.  The average age at death of USTUR registrants is 63 years (range between 25 and 91 years).  The average age of USTUR registrants who are still living is 73 years (range between 30 and 93 years)."
bulletThe only human cases of significant fallout exposure to humans (as of 1964, and outside of the USSR)  were in the Marshall Islands, after a U.S. test (CROSSROADS, Bikini Atoll, 1946). The short term effects were skin burns, nausea, and other symptoms typical of exposure to high radiation doses. Even so, there was only one cancer (leukemia) likely caused by the radiation, 18 years after exposure of a 1 year old. Of the pregnancies in progress at time of exposure, there was one miscarriage (no evidence for or against radiation relationship). The rest produced healthy children. Not surprisingly, there were a large number of cases of thyroid problems, which lead to some reduced growth in children. A study of the 40,000 military members who participated found no scientific evidence of radiation induced cancers.  References are here. These results do not mean that fallout is harmless - far from it, but they show that even radiation intense enough to produce burns and nausea need  not create a significantly   increased risk of cancer.
bulletAlmost all radioactivity in fallout - even in a ground burst - comes from the fission products themselves or transmutation of parts of the weapon. Thus air bursts and ground bursts produce approximately the same amount of radioactive products. However, ground bursts cause much more of the radioactive debris to be deposited within a fallout pattern, rather than distributed (and accordingly diluted and decayed) across the entire planet.
bulletThere is evidence that radiation is beneficial and improves health (radiation hormesis) up to some surprisingly high levels..


More Technical Information

Blast Effects

bulletThe blast effect is primarily determined by the "overpressure" - given in english units in PSI.
bulletThis effect at any distance is proportional to the cube root of the weapons yield. Thus a 20 megaton bomb, which is large by today's standards, will affect only 10 times the radius of a 20 kiloton bomb - which was the yield at Hiroshima.
In Hiroshima, there was a 50% survival rate .12 miles (200 meters) from ground zero. The bomb went off at 1850 feet above ground zero with a yield of about 20kt. Concrete structures at ground zero survived.
In Hiroshima, there was only one known case of burst eardrums among the survivors.
A human being can withstand up to about 35PSI of peak overpressure from a nuclear blast (1% fatality rate).  Your mileage may vary. Thus a human will almost always survive the blast overpressure at approximately the following distances (slant range) from a blast according to the following table:


Distance From Blast to Survive Blast Wave
Yield Distance (mi) Distance (km) Comments
20 kT .35 .56 Hiroshima and Nagasaki
600 kT 1.1 1.8 Typical Strategic US Nuke
20 MT 3.5 5.6 Very Big Bomb
The blast wave can, however, pick people up and throw them. For a 165 pound standing person to be thrown at 20 feet per second, the following table shows the distance from the blast:


Distance From Blast to be Thrown at 20 fps
Yield Distance (mi) Distance (km)
20kT 1.06 1.75
600kT 4.1 6.6
20MT 16.8 27
Max Wind at Distance from Blast
Yield 1 mi
1.6 km
3 mi
4.8 km
10 mi
16 km
30 mi
48 km
20kT 200 mph
89 mps
47 mph
21 mps
5 mph
2 mps
600kT 1000 mph
447 mps
210 mph
94 mps
51 mps
5 mps
20MT off scale 1200 mph
536 mps
195 mph
87 mps
47 mph
21 mps

The greatest danger from the blast wave comes from destruction of structures and the conversion of objects into missiles. The following tables gives the destruction distance from various yields for a few kinds of structures:

Window Breakage
Yield Distance (mi) Distance (km)
20kT 3.2 5.1
600kT 10 16
20MT 32 51
Wood-frame Building Destruction
Yield Distance (mi) Distance (km)
20kT 1.5 1.9
600kT 4.8 7.7
20MT 15 19
Multi-story Brick
Yield Distance (mi) Distance (km)
20kT 1. 1.6
600kT 3.0 4.8
20MT 10 16
Multi-story Reinforced Concrete Offices
Yield Distance (mi) Distance (km)
20kT .5 .81
600kT 1.3 2.1
20MT 5 8.1
bulletA ground burst produces a crater. The following table shows crater sizes:
Crater Sizes
Yield Width
20kT 633 193 80 24
600kT 2112 643 211 64
20MT 7392 2253 792 241

Historic Radiation Releases

Historic Radiation Releases (MegaCuries)
Chernobyl 7.3            MCi
Hiroshima 1.4            MCi
Hanford (I-131 only) 0.74          MCi
Three Mile Island 0.000015 MCi

Nuclear Physics Reference

The negative effects of radiation can be divided into immediate effects (from very high dosages) and long term effects (from lower dosages). Long term effects are thought to be either the development of cancer, or genetic damage passed on to offspring. However, there is no evidence that low to moderate levels of radiation cause any long term damage in humans, and some evidence that it may be beneficial (radiation hormesis). Both long term effects would be a result of damage to DNA - most likely nuclear DNA (as opposed to mitochondrial DNA). However, the human cell experiences an average of 70 million (7x10^7) DNA damages per year. Only 5 of these are attributable to natural radiation. Even radiation much higher than natural radiation would produce a negligible percentage of the total DNA damage. The average natural human dose is 2.2 mSv per year (see below for units). The lethal dose is typically 3000 mSv - 5000 mSv.

Some elements of the following tables of miscellaneous conversion factors areexcerpted from Nuclear Weapons Frequently Asked Questions by Carey Sublette.

Units, Conversions and Physical Constants
Becquerel(Bq) 1 Disintegration/Sec  
Curie (ci) 3.7 1010 Disintegrations/Sec 3.7 1010 Bq
Rad .01 J/kg Radiation Exposure
Sievert (Sv) 100 REM (Grays*Q) Human Radiation Exposure
REM Rads*RBE Human Radiation Exposure
Gray(Gy) 1 J/kg  
Gamma/Xray Roentgen (R) .94 erg/g  
Plutonum 17 ci/g Half Life: 24000 Years
Depleted Uranium 3.6 10-7 ci/g  
Natural Uranium 7 10-7 ci/g contains .7% U235
Enriched Uranium 7 10-7 ci/g  
1 Kiloton (kt) 10^12 calories
4.19x10^12 Joules
2.62x10^25 MeV
fission of approx 57 g of material
1.16x10^t KWH<
1 eV 1.602177x10^12 erg
11606 degrees K
1 Bar 10^5 pascals (nt/m^2)
.98687 atmospheres
14.5038 PSI
Fission of U-235 or Pu-239 approx 17.5 kt/kg  
Fusion of pure deuterium 82.2 kt/kg  
Total mass conversion 21.47 Mt/kg  





Nuclear Weapons Archive and FAQ - This is an outstanding and comprehensive resource.: http://nuclearweaponarchive.org/.

A paper disputing Linear No Threshold Theory (originally found here.)

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