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Kiloton

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Kiloton

"Kiloton" redirects here. For the similarly named weight measurements, see Tonne.

TNT equivalent is a method of quantifying the energy released in explosions. The "ton of TNT" is a unit of energy equal to 4.184 gigajoules, which is approximately the amount of energy released in the detonation of one metric ton of TNT. The "megaton of TNT" is a unit of energy equal to 4.184 petajoules.[1]

The kiloton and megaton of TNT have traditionally been used to rate the energy output, and hence destructive power, of nuclear weapons (see nuclear weapon yield). This unit is written into various nuclear weapon control treaties, and gives a sense of destructiveness as compared with ordinary explosives, like TNT. More recently, it has been used to describe the energy released in other highly destructive events, such as asteroid impacts. However, TNT is not the most energetic of conventional explosives. Dynamite, for example, has about 60% more energy density (approximately 7.5 MJ/kg, compared to about 4.7 MJ/kg for TNT).

Value

A gram of TNT releases 4100–4602 joules upon explosion. To define the tonne of TNT, this was arbitrarily standardized by letting 1 gram TNT = 4184 J (exactly).[2] This conveniently defined the energy liberated by one gram of TNT as exactly one kilocalorie.

This definition is a conventional one. The explosive's energy is normally calculated using the thermodynamic work energy of detonation, which for TNT has been accurately measured at 4686 J/g from large numbers of air blast experiments and theoretically calculated to be 4853 J/g.[3]

The measured pure heat output of a gram of TNT is only 2724 J,[4] but this is not the important value for explosive blast effect calculations.

Alternative TNT equivalency can be calculated depending upon when in the detonation the value is measured and which property is being compared.[5][6][7][8]

A kiloton of TNT can be visualized as a cube of TNT of 8.46 metres (27.8 ft) on a side.

Grams TNT Symbol Tons TNT Symbol Energy
gram of TNT g microton of TNT μt 4.184×103 J
kilogram of TNT kg milliton of TNT mt 4.184×106 J
megagram of TNT Mg ton of TNT t 4.184×109 J
gigagram of TNT Gg kiloton of TNT kt 4.184×1012 J
teragram of TNT Tg megaton of TNT Mt 4.184×1015 J
petagram of TNT Pg gigaton of TNT Gt 4.184×1018 J

Examples

  • Conventional bombs yield range from less than 1 ton to FOAB's 44 tonnes.
  • The MythBusters homemade diamonds episode used 2.5 tons of ANFO to make diamonds.
  • Minor Scale, a 1985 United States conventional explosion utilizing 4,744 tons of ANFO explosive to provide a scaled equivalent airblast of an 8 kiloton (33.44 TJ) nuclear device,[9] is believed to be the largest planned detonation of conventional explosives in history.
  • The Halifax Explosion in 1917 involved the accidental detonation of 3,000 tons of TNT.
  • The Little Boy atomic bomb dropped on Hiroshima on August 6, 1945 exploded with an energy of about 12.5 kilotons of TNT (52 TJ), and the Fat Man atomic bomb dropped on Nagasaki on August 9, 1945 exploded with an energy of about 22 kilotons of TNT (92 TJ). The nuclear weapons currently in the arsenal of the United States range in yield from 0.3 kt (1.3 TJ) to 1.2 Mt (5.0 PJ) equivalent, for the B83 strategic bomb.
  • During the Cold War, the United States developed hydrogen bombs with a maximum theoretical yield of 25 megatons of TNT (100 PJ); the Soviet Union developed a prototype weapon, nicknamed the Tsar Bomba, which was tested at 50 Mt (210 PJ), but had a maximum theoretical yield of 100 Mt (420 PJ).[10] The actual destructive potential of such weapons can vary greatly depending on conditions, such as the altitude at which they are detonated, the nature of the target they are detonated against, and the physical features of the landscape where they are detonated.
  • The energy contained in 1 megaton of TNT (4.2 PJ) is enough to power the average American household (in the year 2007) for 103,474 years.[11] For example, the 30 Mt (130 PJ) estimated upper limit blast power of the Tunguska event could power the aforementioned home for just over 3,104,226 years. To put that in perspective: the blast energy could power the entire United States for 3.27 days.[12]
  • Megathrust earthquakes record huge MW values, or total energy released. The 2004 Indian Ocean Earthquake released 9,560 gigatons of TNT (40,000 EJ) equivalent, but its ME (surface rupture energy, or potential for damage) was far smaller at 26.3 megatons of TNT (110 PJ).
  • The total energy of all explosives used in World War Two (including the Hiroshima and Nagasaki bombs) is estimated to have been 3 megatons of TNT.
  • The total global nuclear arsenal is about 30,000 nuclear warheads with a destructive capacity of 5,000 megatons or 5 gigatons (5,000 million tons) of TNT.
  • The approximate energy released when the largest fragment of Comet Shoemaker–Levy 9 impacted Jupiter was estimated to be equal to 6 million megatons (or 6 trillion tons) of TNT.
  • The maximum theoretical yield from 1 kg of matter by converting all of the mass into energy (by mass–energy equivalence, E = mc2) yields 89.8 petajoules or the equivalent of 21.5 megatons of TNT. No practical method of total conversion exists today, such as combining 500 grams of matter with 500 grams of antimatter. However, in the case of proton–antiproton annihilation, approximately 50% of the released energy will escape in the form of neutrinos, which are almost undetectable.[13] Electron-positron annihilation events emit their energy entirely as gamma rays.
  • The approximate energy released when the Chicxulub impact caused the mass extinction 65 million years ago was estimated to be equal to 100 teratons (i.e. 100 exagrams or approximately 220.462 quadrillion pounds) of TNT. That is roughly 8 billion times stronger than each of the bombs that hit Hiroshima and Nagasaki and the most energetic event on the history of Earth for billions of years, far more powerful than any volcanic eruption, earthquake or firestorm. Such an explosion annihilated everything within a thousand miles of the impact in a split second. Such energy could also power the whole Earth for several centuries.
  • The amount of energy given in the 2011 Tōhoku earthquake and tsunami was more than 200,000 times the surface energy and was calculated by the USGS at 3.9×1022 joules,[14] slightly less than the 2004 Indian Ocean quake. This is equivalent to 9,320 gigatons of TNT, or approximately 600 million times the energy of the Hiroshima bomb.
  • On a much grander scale, supernova explosions give off about 1044 joules of energy, which is about a hundred billion yottatons (ten octillion (1028) megatons) of TNT, equivalent to the explosive force of a quantity of TNT a trillion (1012) times the mass of the planet Earth.

See also

References

  • Guide for the Use of the International System of Units (SI)
  • Nuclear Weapons FAQ Part 1.3
  • Rhodes, Richard. The Making of the Atomic Bomb, New York: Simon and Schuster, 1986.
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