TNT equivalent
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. 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.
Value
A 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).[1]
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.[2]
The measured pure heat output of a gram of TNT is only 652 thermochemical calories ≈ 2728 J,[3] but this is not the important value for explosive blast effects calculations.
| 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
A megaton is a large amount of energy. The atomic bomb dropped on Hiroshima on August 6, 1945 exploded with an energy of about 20 kilotons of TNT (~8.4×1013 joules). Modern nuclear warheads range in yield from 100 kt to 20 Mt TNT equivalent. The largest bomb ever tested, the Tsar Bomba, had a yield of about 50 Mt.
About 1 Mt equivalent exploded on the ground or slightly above ground creates a crater about 0.5 km (0.3 mi) in diameter and levels practically everything in a few kilometer radius.[citation needed] It is enough to crush underground bunkers at a depth of about 300 metres (1000 ft).[4]
See also
References
- ^ NIST Guide for the Use of the International System of Units (SI): Appendix B8 - Factors for Units Listed Alphabetically
- ^ Cooper, Paul. Explosives Engineering, New York: Wiley-VCH, 1996, pp 406.
- ^ "Physics for Future Presidents, a textbook", 2001-2002, Richard A. Muller, Chapter 1. Energy, Power, and Explosions
- ^ Lisbeth Gronlund, David Wright, and Robert Nelson. Earth-Penetrating Weapons (May 2005)
- 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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