1 a measure of explosive power (of an atomic weapon) equal to that of one million tons of TNT
2 one million tons
Etymologymetric prefix mega- + ton
PronunciationIPA (US): /ˈmɛgəˌtʌn/
- a measure of the strength of an explosion or a bomb based on how many million tons of TNT would be needed to produce the same energy.
TNT equivalent is a method of quantifying the energy released in explosions. The tonne of TNT is used as a unit of energy, approximately equivalent to the energy released in the detonation of this amount of TNT.
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.
ValueA gram of TNT releases 980–1100 calories upon explosion. To define the tonne of TNT, this was arbitrarily standardized to 1000 thermochemical calories = 1 gram TNT = 4184 J (exactly). To put this into perspective, a gram of food carbohydrate has approximately 4 kcal of energy, versus 1 kcal for a gram of TNT.
This definition is a conventional one. Explosives' energy is normally calculated using the thermodynamic work energy of detonation, which for TNT has been accurately measured at 1120 calth/g from large numbers of air blast experiments and theoretically calculated to be 1160 calth/g.
The measured pure heat output of a gram of TNT is only 651 thermochemical calories ≈ 2724 J, but this is not the important value for explosive blast effect calculations.
- During the Cold War, the United States developed hydrogen bombs with a maximum theoretical yield of 25 Mt; the Soviet Union developed a prototype weapon, nick-named the Tsar Bomba, which was tested at 50 Mt, but had a maximum theoretical yield of 100 Mt. 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.
- Megathrust earthquakes record huge MW values, or total energy released. The 2004 Indian Ocean Earthquake released 9,560 gigatons of TNT equivalent, but its ME (surface rupture energy, or potential for damage) was far smaller at 26.3 megatons of TNT. The largest quake registered, the 1960 Chilean quake, released MW almost 60,000 gigatons of TNT equivalent.
- On a much grander scale, supernova explosions give off about 1044 joules of energy, which is about ten octillion (1028) megatons of TNT.
By E = mc2, when 1 kilogram of antimatter annihilates with 1 kilogram of matter the reaction produces 1.8 J, which is equal to 42.96 Mt.
- 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.
megaton in Polish: Równoważnik trotylowy wybuchu jądrowego
megaton in Bulgarian: Тротилов еквивалент
megaton in German: TNT-Äquivalent
megaton in Esperanto: TNT-ekvivalento
megaton in Hebrew: טון TNT
megaton in Japanese: TNT換算
megaton in Dutch: TNT-equivalent
megaton in Vietnamese: Đương lượng nổ
megaton in Chinese: 爆炸当量