Bhangmeter
Encyclopedia
A bhangmeter is a type of photometer
used on reconnaissance satellite
s that is intended to detect atmospheric nuclear detonations
.
The first satellites which incorporated bhangmeters were the Advanced Vela satellites
. An earlier generation of Vela satellites had been designed to detect nuclear explosions, but were not equipped with bhangmeters (they used X-ray
sensors instead to detect an intense single pulse of X-rays).
The silicon
photodiode
sensors are designed to detect the distinctive bright double pulse of light that is emitted from atmospheric nuclear weapons explosions. This signature is a short and intense flash lasting around 1 millisecond, followed by a second much more prolonged and less intense emission of light taking a fraction of a second to several seconds to build up. The effect occurs because the surface of the early fireball is quickly overtaken by the expanding atmospheric shock wave composed of ionised gas. Although it emits a considerable amount of light itself, it is opaque and prevents the far brighter fireball from shining through. As the shock wave expands, the amount of light it emits increases with its surface area. The effect is unambiguous below about 30 km altitude, but above this height a more ambiguous single pulse is produced.
The name of the detector is a playful pun
, which was bestowed upon it by Fred Reines, one of the scientists working on the project. The name is derived from the Indian word "bhang
", a locally grown variety of cannabis
which is smoked or drunk to induce intoxicating effects, the joke being that one would have to be on drugs to believe the bhangmeter detectors would work properly. This is a contrast to the similarly-pronounced "bangmeter" one might associate with detection of nuclear explosions.
Photometer
In its widest sense, a photometer is an instrument for measuring light intensity or optical properties of solutions or surfaces. Photometers are used to measure:*Illuminance*Irradiance*Light absorption*Scattering of light*Reflection of light*Fluorescence...
used on reconnaissance satellite
Spy satellite
A spy satellite is an Earth observation satellite or communications satellite deployed for military or intelligence applications....
s that is intended to detect atmospheric nuclear detonations
Nuclear explosion
A nuclear explosion occurs as a result of the rapid release of energy from an intentionally high-speed nuclear reaction. The driving reaction may be nuclear fission, nuclear fusion or a multistage cascading combination of the two, though to date all fusion based weapons have used a fission device...
.
The first satellites which incorporated bhangmeters were the Advanced Vela satellites
Vela (satellite)
Vela was the name of a group of satellites developed as the Vela Hotel element of Project Vela by the United States to monitor compliance with the 1963 Partial Test Ban Treaty by the Soviet Union, and other nuclear-capable states. It means vigil or "watch" in Spanish.Vela started out as a small...
. An earlier generation of Vela satellites had been designed to detect nuclear explosions, but were not equipped with bhangmeters (they used X-ray
X-ray
X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...
sensors instead to detect an intense single pulse of X-rays).
The silicon
Silicon
Silicon is a chemical element with the symbol Si and atomic number 14. A tetravalent metalloid, it is less reactive than its chemical analog carbon, the nonmetal directly above it in the periodic table, but more reactive than germanium, the metalloid directly below it in the table...
photodiode
Photodiode
A photodiode is a type of photodetector capable of converting light into either current or voltage, depending upon the mode of operation.The common, traditional solar cell used to generateelectric solar power is a large area photodiode....
sensors are designed to detect the distinctive bright double pulse of light that is emitted from atmospheric nuclear weapons explosions. This signature is a short and intense flash lasting around 1 millisecond, followed by a second much more prolonged and less intense emission of light taking a fraction of a second to several seconds to build up. The effect occurs because the surface of the early fireball is quickly overtaken by the expanding atmospheric shock wave composed of ionised gas. Although it emits a considerable amount of light itself, it is opaque and prevents the far brighter fireball from shining through. As the shock wave expands, the amount of light it emits increases with its surface area. The effect is unambiguous below about 30 km altitude, but above this height a more ambiguous single pulse is produced.
The name of the detector is a playful pun
Pun
The pun, also called paronomasia, is a form of word play which suggests two or more meanings, by exploiting multiple meanings of words, or of similar-sounding words, for an intended humorous or rhetorical effect. These ambiguities can arise from the intentional use and abuse of homophonic,...
, which was bestowed upon it by Fred Reines, one of the scientists working on the project. The name is derived from the Indian word "bhang
Bhang
Bhang is a preparation from the leaves and flowers of the female cannabis plant, smoked or consumed as a beverage in the Indian subcontinent.- India:...
", a locally grown variety of cannabis
Cannabis (drug)
Cannabis, also known as marijuana among many other names, refers to any number of preparations of the Cannabis plant intended for use as a psychoactive drug or for medicinal purposes. The English term marijuana comes from the Mexican Spanish word marihuana...
which is smoked or drunk to induce intoxicating effects, the joke being that one would have to be on drugs to believe the bhangmeter detectors would work properly. This is a contrast to the similarly-pronounced "bangmeter" one might associate with detection of nuclear explosions.