Discover

(Redirected from Nuclear weapons yield)

The explosive 'yield of a nuclear weapon' is the amount of energy, called the yield, discharged when a nuclear weapon is detonated, expressed usually in the equivalent mass of trinitrotoluene (TNT), either in kilotons (thousands of tons of TNT) or megatons (millions of tons of TNT), but sometimes also in terajoules (1 kiloton of TNT = 4.184 TJ). Because the precise amount of energy released by TNT is and was subject to measurement uncertainties, especially at the dawn of the nuclear age, the accepted convention is that one kt of TNT is simply defined to be $10^\{12\}$ calories equivalent, this being very roughly equal to the energy yield of 1,000 tons of TNT.

Contents

Examples of nuclear weapon yields

Yield limits

Calculating yields and controversy

See also

External links

Examples of nuclear weapon yields

In order of increasing yield (most yield figures are approximate):

★ Davy Crockett tactical nuclear weapon: variable yield 0.01–1 kt — mass only 23 kg (51 lb), lightest ever deployed by the United States (same warhead as Special Atomic Demolition Munition and GAR-11 Nuclear Falcon missile).

★ Hiroshima's "Little Boy" gravity bomb: 12–15 kt — gun type uranium-235 fission bomb (the first of the two nuclear weapons that have been used in warfare).

★ Nagasaki's "Fat Man" gravity bomb: 20–22 kt — implosion type Plutonium-239 fission bomb (the second of the two nuclear weapons used in warfare).

★ W76 warhead 100 kt (12 of these may be in a MIRVed Trident II missile; treaty limited to 8).

★ B61 nuclear bomb: Mod 7 (up to 350 kt), Mod 10 (4 yield options: 0.3 kt, 1.5 kt, 60 kt, and 170 kt), and Mod 11 (undisclosed yield).

★ W87 warhead: 300 kt (10 of these were in a MIRVed LG-118A Peacekeeper).

★ W88 warhead: 475 kt (12 of these may be in a Trident II missile; treaty limited to 8).

★ ''Ivy King'' device: 500 kt — second most powerful pure fission bomb [UK Orange Herald: 700kt]; 60 kg uranium; implosion type.

★ B83 nuclear bomb: variable, up to 1.2 Mt; most powerful U.S. weapon in active service.

★ B53 nuclear bomb: 9Mt, most powerful US warhead; no longer in active service, but 50 are retained as part of the "Hedge" portion of the Enduring Stockpile; similar to the W-53 warhead that has been used in the Titan II Missile, decommissioned in 1987.

★ ''Castle Bravo'' device: 15 Mt — most powerful US test.

★ EC17/Mk-17, the EC24/Mk-24, and the B41 (Mk-41) (most powerful US weapons ever: 25 Mt; the Mk-17 was also the largest by size and mass: ca. 20 tons; the Mk-41 had a mass of 4800 kg; gravity bombs carried by B-36 bomber (retired by 1957).

★ The entire Operation Castle nuclear test series: 48.2 Mt — the highest-yielding test series conducted by the U.S.



★ ''Tsar Bomba'' device: 50 Mt — USSR, most powerful explosive device ever, mass of 27 short tons (24 metric tons), in its "full" form (i.e. with a depleted uranium tamper instead of one made of lead) it would have been 100 Mt.

★ All nuclear testing: 510.4 Mt — total megatonnage expended during all nuclear testing.[1]
As a comparison, the blast yield of the GBU-43 Massive Ordnance Air Blast bomb (perhaps the most powerful non-nuclear weapon ever designed) is 0.011 kt, and that of the Oklahoma City bombing, using a truck-based fertilizer bomb, was 0.002 kt. Most artificial non-nuclear explosions are considerably smaller than even what are considered to be very small nuclear weapons.

Yield limits

The yield-to-weight ratio is the amount of weapon yield compared to the mass of the weapon. The theoretical maximum yield-to-weight ratio for fusion weapons is 6 Megatons per metric ton (6 Mt/t). [2] The practical achievable limit is somewhat lower. Though the United States did claim they had the capability of tipping a Titan II ICBM with a 35 Mt fusion bomb. If this is the case the yield to weight ratio would be about 9.5 Mt/t (kt/kg). For current US weapons 600 kt/t (2.5 TJ/kg) to 2.2 Mt/t (9.2 TJ/kg). By comparison, for the Davy Crockett it was 0.4 - 40 kt/t (0.002 - 0.167 TJ/kg), for Little Boy 4 kt/t, and for the Tsar Bomba 2 Mt/t (8 TJ/kg) (deliberately reduced from the possible maximum which was twice as much), and for the Mk-41 5.2 Mt/t.
The largest pure-fission bomb ever constructed had a 500 kt yield, which is probably in the range of the upper limit on such designs. Fusion boosting could likely raise the efficiency of such a weapon significantly, but eventually all fission-based weapons have an upper yield due to the difficulties of dealing with large critical masses. However there is no known upper yield limit for a fusion (e.g, hydrogen) bomb. In principle a fusion bomb could be many thousand megatons. Because of the maximum theoretical yield-to-weight ratio is about 6Mt/t, and the maximum achievable ratio about 5.2 MT/t, there is a practical limit on air delivery of the weapon.
For example, if the full payload of 250 t of the Antonov An-225 could be used, the limit would be 250 t
★ 5.2 Mt/t, or 1300 Mt. Likewise the maximum limit of a missile-delivered weapon is determined by the missile payload capacity. The large Russian SS-18 ICBM has a payload capacity of 7,200 kg, so the calculated maximum delivered yield would be 37.4 Mt. In fact the SS-18 mod 1 yield for a single warhead is about 24 Mt. [3] In more recent practice, large single warheads are seldom used, since smaller MIRV warheads are more destructive for a given total yield or payload capacity.

Calculating yields and controversy

Yields of nuclear explosions can be very hard to calculate, even using numbers as rough as in the kiloton or megaton range (much less down to the resolution of individual terajoules). Even under very controlled conditions, precise yields can be very hard to determine, and for less controlled conditions the margins of error can be quite large. Yields can be calculated in a number of ways, including calculations based on blast size, blast brightness, seismographic data, and the strength of the shock wave. Enrico Fermi famously made a (very) rough calculation of the yield of the Trinity test by dropping small pieces of paper in the air and measuring at how far they were moved by the shock wave of the explosion.

A good approximation of the yield of the Trinity test device was obtained from simple dimensional analysis by the British physicist G. I. Taylor. Taylor noted that the radius ''R'' of the blast should initially depend only on the energy ''E'' of the explosion, the time ''t'' after the detonation, and the density ρ of the air. The only dimensionless number that can be constructed from these quantities is:

ho,{R}^{5}}}
Determining the value of ''c'' theoretically would require an understanding of the complicated fluid dynamics of the problem, but on general grounds Taylor expected it to be of order of magnitude 1 (experimentally it turns out to be about 1.03). Using the picture of the Trinity test shown here (which had been publicly released by the U.S. government and published in ''Life'' magazine), Taylor estimated that at ''t'' = 0.025 s the blast radius was 140 m. Taking ρ to be 1 kg/m³ and solving for ''E'', he obtained that the yield was about 9e13 J, or 22 kilotons. This very simple argument agrees within 10% with the official value of the bomb's yield, 20 kilotons, which at the time that Taylor published his result was considered highly-classified information. (See G. I. Taylor, ''Proc. Roy. Soc. London'' 'A201', pp. 159, 175 (1950).)
Where this data is not available, as in a number of cases, precise yields have been in dispute, especially when they are tied to questions of politics. The weapons used in the atomic bombings of Hiroshima and Nagasaki, for example, were highly individual and very idiosyncratic designs, and gauging their yield retrospectively has been quite difficult. The Hiroshima bomb, "Little Boy", is estimated to have been between 12 and 18 kt (a 20% margin of error), while the Nagasaki bomb, "Fat Man", is estimated to be between 18 and 23 kt (a 10% margin of error). Such apparently small changes in values can be important when trying to use the data from these bombings as reflective of how other bombs would behave in combat, and also result in differing assessments of how many "Hiroshima bombs" other weapons are equivalent to (for example, the Ivy Mike hydrogen bomb was equivalent to either 867 or 578 Hiroshima weapons — a rhetorically quite substantial difference — depending on whether one uses the high or low figure for the calculation). Other disputed yields have included the massive Tsar Bomba, whose yield was claimed between being "only" 50 Mt or at a maximum of 57 Mt by differing political figures, either as a way for hyping the power of the bomb or as an attempt to undercut it.
Nuclear testing yields, as in the Tsar Bomba example, can also be used as a way of reflecting upon technical expertise, and claiming higher yields or accusations of lower yields can be used as a way of promoting or disparaging the technical abilities of a nuclear program. When India claimed to have successfully detonated a hydrogen bomb in their 1998 Operation Shakti tests, many Western observers relied on analysis of seismographic data to determine whether the Indian tests reflected a successful hydrogen bomb detonation. Some have alleged that India's reported yields have been higher than their actual test yields, a move which would apparently be for political purposes (to claim more nuclear ability than their rival Pakistan, for example, or to demonstrate their military might to other potential rivals such as nearby China) if true.

See also

★ Effects of nuclear explosions — goes into detail about different effects at different yields

External links

★ "What was the yield of the Hiroshima bomb?" (excerpt from official report)

★ "General Principles of Nuclear Explosions", Chapter 1 in Samuel Glasstone and Phillip Dolan, eds., ''The Effects of Nuclear Weapons'', 3rd edn. (Washington D.C.: U.S. Department of Defense/U.S. Energy Research and Development Administration, 1977); provides information about the relationship of nuclear yields to other effects (radiation, damage, etc.).

★ "THE MAY 1998 POKHRAN TESTS: Scientific Aspects", discusses different methods used to determine the yields of the Indian 1998 tests.

★ Discusses some of the controversy over the Indian test yields

★ "What are the real yields of India's nuclear tests?" from Carey Sublette's NuclearWeaponArchive.org

★ High-Yield Nuclear Detonation Effects Simulator