RAY & PARTICLES | TECHNO·SCIENTIFIC APPLICATIONS
Electro·magnetic radiation is a combination of oscillating electric and magnetic fields propagating through space which carry energy from one place to the other. Contrary to other kinds of waves [like soundwaves] electro·magnetic radiation can propagate through vacuum since an electric field variating in time generates a magnetic field and, the other way round, the temporal variation of a magnetic field generates an electric field. Thus, you can visualise electro·magnetic radiation as two fields constantly generating each another.
Maxwell's equations also predict its propagation velocity through vacuum [299.792 km/s] and its direction [always perpendicular to the oscillation within the electric and magnetic fields which, in turn, are perpendicular to each other].
Depending on the wavelength, electro·magnetic radiation receives different denominations, ranging from the energetic gamma·rays [with a wavelength of several picometres] to radio·waves [with a wavelength of kilometres], and passing through the visible light [with a wavelength within the range of decimals of a micrometre]. The complete range of wavelengths is called the electro·magnetic spectrum.
. . . . . . . . . . . . . . . . . . . . . . .
:: the visible spectrum
Visible light is a tiny interval ranging from the violet wavelength [around 400 nanometres] to the red wavelength [around 700 nm, being a nanometre 10 to the -9 metres].
When a ray of light changes its medium of propagation it disperses in different ways for each colour [that is, for each wavelength]. The typical example to illustrate this property is the white light decomposition produced when a white beams goes through a prism.
visible light spectrum
. . . . . . . . . . . . . . . . . . . . . . .
:: infrared spectrum
: tele·communications
Telecommunication is the transmission of signals over a distance for the purpose of communication. In modern times, this process almost always involves the sending of electro·magnetic waves by electronic transmitters. The basic elements of a telecommunication system are:
· a transmitter that takes information and converts it to a signal for transmission
· a transmission medium over which the signal is transmitted
· a receiver that receives and converts the signal back into usable information
An antenna or aerial is an arrangement of aerial electrical conductors designed to transmit or receive radio·waves. Physically, it's an arrangement of conductors that generate a radiating electromagnetic field in response to an applied alternating voltage and its associated alternating electric current, or can be placed in an electro·magnetic field so that the field will induce an alternating current in the antenna and a voltage between its terminals. The electro·magnetic radiation propagates in the same frequency as the alternating voltage.
In tele·communications the waves are classified based on an international agreement of frequencies determined by their applications:
· radio·waves | William Herz
The first implemented communication system through radio·waves was designed by the Italian Guglielmo Marconi, who in 1901 carried out the first radio·electric transatlantic transmission giving birth to wireless telegraphy. Other inventors, like Ørsted, Faraday, Hertz, Tesla and Edison had previously carried out studies and experiments in this field, which served as a base for Marconi's work.
Depending on its frequency, electro·magnetic waves cannot propagate through certain media. That is why radio transmissions don't work underwater and mobile phones get out of range when inside a metal box.
: television
The principle is the same, though in this case the radio signal receiver is a television set. In 1894 German student Paul Nipkow developed and patented the first electro·mechanic television system [Nipkow's disc].
Anyway, it wasn't until 1907 when the amplification tubes technology was developed and his design was finally applicable. In 1911, Boris Rosing and his student Vladimir Kosma Zworykin created a television system that scanned images through a mirrored·drum and transmitted "crude images" through an electronic Braun tube [the cathode·ray tube] into a receiver. It wasn't yet possible to get moving images because the scan sensibility "wasn't enough and the selenium cell always lagged behind”.
The final solution was first described by the Hungarian inventor Kálmán Tihanyi in 1926, refined and patented in 1928. On the 25th of March 1925, Scottish inventor John Logie Baird offered the first public demonstration of a working television system to the members of the Royal Institution; and on the 26th of January 1926, to a reporter in his laboratory in London. Contrary to previous electronic systems with a resolution of many hundreds of lines, the image vertically scanned by Baird had only 30 lines!, just enough to reproduce a recognisable human face. In 1927, Baird transmitted a signal along a phoneline over the 438 miles between London and Glasgow. In 1928, his company carried out the first transatlantic television signal transmission between London and New York.
: thermo radiation
This is a range of electro·magnetic radiation with a wavelength lower than a microwave [between 700 nm. and 1 millimetre, the longest colour wavelength in the visible spectrum]. It was discovered in 1800 by the astronomer William Herschel.
Due to its energetic properties, matter produces radiation. All living beings [mammals especially] emit a great part of this radiation in the infrared spectrum associated to their body temperature.
Infrared radiation is used by night·vision equipment when the amount of visible light is insufficient to see objects directly. The radiation is received and reflected on a screen, being brighter those objects of higher temperatures.
Infrared photography [of military origin] was basically used to detect camouflage; but nowadays it has several technical and scientific applications in archaeology, climatology and geology.
infrared images of a body in a sauna and of planet Earth
By the way, infrared radiation is also used at short distances to communicate computers with their printers or television sets with their remote controls...
: magnetic resonance imaging [MRI]
Magnetic Resonance Imaging uses radio electro·magnetic radiation and therefore, its relatively lower energy doesn't cause as much damage as ultraviolet radiation [x and y rays].
For the test, the patient lies inside a big cylindrical magnet that emits radio·waves 10.000 to 30.000 stronger than the Earth's magnetic field. The radiation affects the atoms in the body forcing the nucleai to change position. When returning to their original place, the nucleai produce their own radio·waves. The scanner identifies them and transfers them to a computer, where they're translated into an image. Since our bodies consist mostly of water [and water consists mostly of hydrogen atoms] hydrogen atomic nucleai are mostly used for this kind of scans.
Some tissues contain a small amount of hydrogen atoms [like bones], so they appear dark; while tissues with higher amounts of hydrogen [like fatty tissue] appear much brighter.
Computed Tomography can only create horizontal images, but MRI is capable of creating images from practically all possible angles.
. . . . . . . . . . . . . . . . . . . . . . .
:: ultraviolet spectrum
: medical applications
Plenty of time has passed since the ElectroCardioGram's invention [ECG], a test that registers the heart's electrical activity by placing a standard number of electrodes on strategic places of the body. The results are registered on a millimetered sheet of paper like this one:
By the late XIX century the famous X·rays add some spark to the representation of our inner structure, when the German physicist Wilhelm Conrad Roentgen discovered them by chance while studying the cathode rays inside a high voltage tube. It is a kind of penetrating electro·magnetic radiation with a wavelength ranging from 10nm to 0.0001 nm, even stronger than ultraviolet. The shorter a wavelength of a x·ray, the higher their energy and power penetration.
X·rays are always produced when bombarding a material object with high speed electrons. A big amount of the electrons' energy is lost as heat [infrared]; the rest produces x·rays when the target's atoms change as a result of the impact.
The implementation of electronic equipment in medicine provides ever increasing "dimensions" to our inner structure, allowing us to represent our tissues, bones, etc. with amazing accuracy. The following are just a few examples:
: computed tomography [CT scan]
It's a radiographic technique where a computer generates transversal images of the heart. The patient lies inside a large and narrow tube [the tomographer, very similar to the MR chamber] that contains an x·ray generator. In some cases, patients are injected a contrasting medium in their blood to get a clearer picture.
More recently, new technologies allow the technicians to align and join different images obtained by CT scan [always transversal cuts] to produce a threedimensional image that can be turned and studied from any angle.
: positron emission tomography [PET SCAN]
Particle physicists regularly produce collisions between electrons and their anti·particles [positrons] to probe matter and the fundamental forces at high energy levels. When an electron and a positron meet, they annihilate creating matter that, at high energy levels, can rematerialise into new particles and anti·particles.
At low energy levels, however, these annihilations between electrons and positrons are used to reveal how an organ works thanks to the technique known as Positron Emission Tompgraphy [PET scan]. The positrons come from a decayed radioactive nucleus injected to the patient in a special fluid. The positrons annihilate the electrons of the nearby atoms, but since the pair is in an almost stationary state when they meet, there isn't enough energy to create even the tinniest particle and anti·particle, so the resultant energy emerges as 2 gamma rays thriving away in opposite directions. These rays allow the technicians to reconstruct the contact surface between matter and anti·matter representing it in 2d and 3d.
PET scan is actually a combination of nuclear medicine and biochemical analysis that helps to visualise the bio·chemical changes inside the body, like the cardiac muscle's metabolism. The difference between this study and other nuclear tests is that the PET detects the metabolism inside the body tissues, while the others detect the amount of radioactive substance accumulated in the body tissues within a specific area to evaluate the state of that tissue.
: y·rays [gamma]
Gamma·ray photons are forms of electro·magnetic radiation of a specific frequency [the highest in the spectrum] produced by the interaction between subatomic particles, like electron·positron annihilation or radioactive decay. Most gamma·rays that interact with our lives come from nuclear reactions in outer space, but at a domestic level they're mostly used for the sterilisation of medical equipment [they can annihilate all kinds of bacteria].
Due to their tissue-penetration properties, they're also used for CT Scans and radiotherapy. However, as ionising radiation, they may cause molecular changes inducing cancer. Though it may sound strange, gamma·rays are also used to treat certain types of cancer through surgery: by concentrating multiple gamma·beams on a single tumour cancer cells can be exterminated. The beams possess different angles to focus radiation to the highest precision, thus minimising the damage to nearby tissue.
: astrophysical applications
You can get plenty information on objects' physical properties through the study of their electro·magnetic spectrum, either through the light they emit [dark body radiation] or the light they absorbe. This is the spectroscopy and it's widely used in astrophysics.
Ultraviolet astronomy uses a kind of electro·magnetic radiation of wavelengths ranging approximately from 400nm to 15 nm, right where the x·rays start. Ultraviolet radiation can be artificially produced using arch lamps; the natural ones come mostly from the sun. This kind of astronomy has been practised since the early 1960's using detectors attached to artificial satellites which provide data on stellar objects. One of these satellites is the International Ultraviolet Explorer launched in 1978.
Gamma·rays also allow us to study and create images of bodies which we cannot access through more conventional means. Like for instance… a micro·quasar!
. . . . . . . . . . . . . . . . . . . . . . .
:: soundwaves applications
Sonar [Sound Navigation And Ranging] is, basically, a navigation and localisation system very similar to the Radar, but instead of producing radio·frequency signals, it emits ultrasonic pulses. It's mostly used for underwater navigation, since electro·magnetic waves cannot propagate under water.
It's composed of a transmitter, an emitter, a receiver and an indicator. The transmitter emits a beam of ultrasonic pulses through the emitter. When these bump against an object, the pulses are reflected back and produce an echo signal that's captured by the receiver. The receiver amplifies the energy of the echo·waves and sends a signal to the indicator, which, finally, produces an image of the object.
Some animals possess a "natural sonar" system; the dolphins, for instance, use it to orientate themselves in turbulent waters, or to hunt safely. Bats also use it for orientation and to hunt in the dark: they emit short ultrasonic vibrations that bounce back after hitting some matter. Differences in the received echoes indicate them where the potential prey is.
: echography
Like the sonar system, in echographies an ultrasound device is used to generate and receive hundreds of high frequency soundwaves that cannot be perceived by the human ear. These waves are momentarily absorbed by the human tissues, bones and body fluids [all of them with different densities] and then bounce back to create an ultrasound image very much like a negative picture; black areas indicate liquid media [like amniotic fluid] and grey or white indicate higher density areas, like tissues or bones.
Ultrasound frequencies are measured in Megahertz and usually range from 3 to 7.5 MHz. Like in electro·magnetic radiation, the lower the frequency, the farther [or deeper] the soundwaves can penetrate body tissues.
Nowadays the ultrasound technique has been improved to the point of even producing colour or 3d images.
Electro·magnetic radiation is a combination of oscillating electric and magnetic fields propagating through space which carry energy from one place to the other. Contrary to other kinds of waves [like soundwaves] electro·magnetic radiation can propagate through vacuum since an electric field variating in time generates a magnetic field and, the other way round, the temporal variation of a magnetic field generates an electric field. Thus, you can visualise electro·magnetic radiation as two fields constantly generating each another.
Maxwell's equations also predict its propagation velocity through vacuum [299.792 km/s] and its direction [always perpendicular to the oscillation within the electric and magnetic fields which, in turn, are perpendicular to each other].
Depending on the wavelength, electro·magnetic radiation receives different denominations, ranging from the energetic gamma·rays [with a wavelength of several picometres] to radio·waves [with a wavelength of kilometres], and passing through the visible light [with a wavelength within the range of decimals of a micrometre]. The complete range of wavelengths is called the electro·magnetic spectrum.
. . . . . . . . . . . . . . . . . . . . . . .
:: the visible spectrum
Visible light is a tiny interval ranging from the violet wavelength [around 400 nanometres] to the red wavelength [around 700 nm, being a nanometre 10 to the -9 metres].
When a ray of light changes its medium of propagation it disperses in different ways for each colour [that is, for each wavelength]. The typical example to illustrate this property is the white light decomposition produced when a white beams goes through a prism.
visible light spectrum
. . . . . . . . . . . . . . . . . . . . . . .
:: infrared spectrum
: tele·communications
Telecommunication is the transmission of signals over a distance for the purpose of communication. In modern times, this process almost always involves the sending of electro·magnetic waves by electronic transmitters. The basic elements of a telecommunication system are:
· a transmitter that takes information and converts it to a signal for transmission
· a transmission medium over which the signal is transmitted
· a receiver that receives and converts the signal back into usable information
An antenna or aerial is an arrangement of aerial electrical conductors designed to transmit or receive radio·waves. Physically, it's an arrangement of conductors that generate a radiating electromagnetic field in response to an applied alternating voltage and its associated alternating electric current, or can be placed in an electro·magnetic field so that the field will induce an alternating current in the antenna and a voltage between its terminals. The electro·magnetic radiation propagates in the same frequency as the alternating voltage.
In tele·communications the waves are classified based on an international agreement of frequencies determined by their applications:
| Range | Denomination | Application | |
| VLF | 10 kHz to 30 kHz | Very low frequency | Long range Radio |
| LF | 30 kHz to 300 kHz | Low frequency | Radio, navigation |
| MF | 300 kHz to 3 MHz | Medium frequency | Medium wl. Radio |
| HF | 3 MHz to 30 MHz | High frequency | Short wl. radio |
| VHF | 30 MHz to 300 MHz | Very high frequency | TV, radio |
| UHF | 300 MHz to 3 GHz | Ultra high frequency | TV, radar |
| SHF | 3 GHz to 30 GHz | Super high frequency | Radar |
| EHF | 30 GHz to 300 GHz | Extra high frequency | Radar |
· radio·waves | William Herz
The first implemented communication system through radio·waves was designed by the Italian Guglielmo Marconi, who in 1901 carried out the first radio·electric transatlantic transmission giving birth to wireless telegraphy. Other inventors, like Ørsted, Faraday, Hertz, Tesla and Edison had previously carried out studies and experiments in this field, which served as a base for Marconi's work.
Depending on its frequency, electro·magnetic waves cannot propagate through certain media. That is why radio transmissions don't work underwater and mobile phones get out of range when inside a metal box.
: television
The principle is the same, though in this case the radio signal receiver is a television set. In 1894 German student Paul Nipkow developed and patented the first electro·mechanic television system [Nipkow's disc].
Anyway, it wasn't until 1907 when the amplification tubes technology was developed and his design was finally applicable. In 1911, Boris Rosing and his student Vladimir Kosma Zworykin created a television system that scanned images through a mirrored·drum and transmitted "crude images" through an electronic Braun tube [the cathode·ray tube] into a receiver. It wasn't yet possible to get moving images because the scan sensibility "wasn't enough and the selenium cell always lagged behind”.
The final solution was first described by the Hungarian inventor Kálmán Tihanyi in 1926, refined and patented in 1928. On the 25th of March 1925, Scottish inventor John Logie Baird offered the first public demonstration of a working television system to the members of the Royal Institution; and on the 26th of January 1926, to a reporter in his laboratory in London. Contrary to previous electronic systems with a resolution of many hundreds of lines, the image vertically scanned by Baird had only 30 lines!, just enough to reproduce a recognisable human face. In 1927, Baird transmitted a signal along a phoneline over the 438 miles between London and Glasgow. In 1928, his company carried out the first transatlantic television signal transmission between London and New York.
: thermo radiation
This is a range of electro·magnetic radiation with a wavelength lower than a microwave [between 700 nm. and 1 millimetre, the longest colour wavelength in the visible spectrum]. It was discovered in 1800 by the astronomer William Herschel.
Due to its energetic properties, matter produces radiation. All living beings [mammals especially] emit a great part of this radiation in the infrared spectrum associated to their body temperature.
Infrared radiation is used by night·vision equipment when the amount of visible light is insufficient to see objects directly. The radiation is received and reflected on a screen, being brighter those objects of higher temperatures.
Infrared photography [of military origin] was basically used to detect camouflage; but nowadays it has several technical and scientific applications in archaeology, climatology and geology.
infrared images of a body in a sauna and of planet Earth
By the way, infrared radiation is also used at short distances to communicate computers with their printers or television sets with their remote controls...
: magnetic resonance imaging [MRI]
Magnetic Resonance Imaging uses radio electro·magnetic radiation and therefore, its relatively lower energy doesn't cause as much damage as ultraviolet radiation [x and y rays].
For the test, the patient lies inside a big cylindrical magnet that emits radio·waves 10.000 to 30.000 stronger than the Earth's magnetic field. The radiation affects the atoms in the body forcing the nucleai to change position. When returning to their original place, the nucleai produce their own radio·waves. The scanner identifies them and transfers them to a computer, where they're translated into an image. Since our bodies consist mostly of water [and water consists mostly of hydrogen atoms] hydrogen atomic nucleai are mostly used for this kind of scans.
Some tissues contain a small amount of hydrogen atoms [like bones], so they appear dark; while tissues with higher amounts of hydrogen [like fatty tissue] appear much brighter.
Computed Tomography can only create horizontal images, but MRI is capable of creating images from practically all possible angles.
. . . . . . . . . . . . . . . . . . . . . . .
:: ultraviolet spectrum
: medical applications
Plenty of time has passed since the ElectroCardioGram's invention [ECG], a test that registers the heart's electrical activity by placing a standard number of electrodes on strategic places of the body. The results are registered on a millimetered sheet of paper like this one:
By the late XIX century the famous X·rays add some spark to the representation of our inner structure, when the German physicist Wilhelm Conrad Roentgen discovered them by chance while studying the cathode rays inside a high voltage tube. It is a kind of penetrating electro·magnetic radiation with a wavelength ranging from 10nm to 0.0001 nm, even stronger than ultraviolet. The shorter a wavelength of a x·ray, the higher their energy and power penetration.
X·rays are always produced when bombarding a material object with high speed electrons. A big amount of the electrons' energy is lost as heat [infrared]; the rest produces x·rays when the target's atoms change as a result of the impact.
The implementation of electronic equipment in medicine provides ever increasing "dimensions" to our inner structure, allowing us to represent our tissues, bones, etc. with amazing accuracy. The following are just a few examples:
: computed tomography [CT scan]
It's a radiographic technique where a computer generates transversal images of the heart. The patient lies inside a large and narrow tube [the tomographer, very similar to the MR chamber] that contains an x·ray generator. In some cases, patients are injected a contrasting medium in their blood to get a clearer picture.
More recently, new technologies allow the technicians to align and join different images obtained by CT scan [always transversal cuts] to produce a threedimensional image that can be turned and studied from any angle.
: positron emission tomography [PET SCAN]
Particle physicists regularly produce collisions between electrons and their anti·particles [positrons] to probe matter and the fundamental forces at high energy levels. When an electron and a positron meet, they annihilate creating matter that, at high energy levels, can rematerialise into new particles and anti·particles.
At low energy levels, however, these annihilations between electrons and positrons are used to reveal how an organ works thanks to the technique known as Positron Emission Tompgraphy [PET scan]. The positrons come from a decayed radioactive nucleus injected to the patient in a special fluid. The positrons annihilate the electrons of the nearby atoms, but since the pair is in an almost stationary state when they meet, there isn't enough energy to create even the tinniest particle and anti·particle, so the resultant energy emerges as 2 gamma rays thriving away in opposite directions. These rays allow the technicians to reconstruct the contact surface between matter and anti·matter representing it in 2d and 3d.
PET scan is actually a combination of nuclear medicine and biochemical analysis that helps to visualise the bio·chemical changes inside the body, like the cardiac muscle's metabolism. The difference between this study and other nuclear tests is that the PET detects the metabolism inside the body tissues, while the others detect the amount of radioactive substance accumulated in the body tissues within a specific area to evaluate the state of that tissue.
: y·rays [gamma]
Gamma·ray photons are forms of electro·magnetic radiation of a specific frequency [the highest in the spectrum] produced by the interaction between subatomic particles, like electron·positron annihilation or radioactive decay. Most gamma·rays that interact with our lives come from nuclear reactions in outer space, but at a domestic level they're mostly used for the sterilisation of medical equipment [they can annihilate all kinds of bacteria].
Due to their tissue-penetration properties, they're also used for CT Scans and radiotherapy. However, as ionising radiation, they may cause molecular changes inducing cancer. Though it may sound strange, gamma·rays are also used to treat certain types of cancer through surgery: by concentrating multiple gamma·beams on a single tumour cancer cells can be exterminated. The beams possess different angles to focus radiation to the highest precision, thus minimising the damage to nearby tissue.
: astrophysical applications
You can get plenty information on objects' physical properties through the study of their electro·magnetic spectrum, either through the light they emit [dark body radiation] or the light they absorbe. This is the spectroscopy and it's widely used in astrophysics.
Ultraviolet astronomy uses a kind of electro·magnetic radiation of wavelengths ranging approximately from 400nm to 15 nm, right where the x·rays start. Ultraviolet radiation can be artificially produced using arch lamps; the natural ones come mostly from the sun. This kind of astronomy has been practised since the early 1960's using detectors attached to artificial satellites which provide data on stellar objects. One of these satellites is the International Ultraviolet Explorer launched in 1978.
Gamma·rays also allow us to study and create images of bodies which we cannot access through more conventional means. Like for instance… a micro·quasar!
. . . . . . . . . . . . . . . . . . . . . . .
:: soundwaves applications
Sonar [Sound Navigation And Ranging] is, basically, a navigation and localisation system very similar to the Radar, but instead of producing radio·frequency signals, it emits ultrasonic pulses. It's mostly used for underwater navigation, since electro·magnetic waves cannot propagate under water.
It's composed of a transmitter, an emitter, a receiver and an indicator. The transmitter emits a beam of ultrasonic pulses through the emitter. When these bump against an object, the pulses are reflected back and produce an echo signal that's captured by the receiver. The receiver amplifies the energy of the echo·waves and sends a signal to the indicator, which, finally, produces an image of the object.
Some animals possess a "natural sonar" system; the dolphins, for instance, use it to orientate themselves in turbulent waters, or to hunt safely. Bats also use it for orientation and to hunt in the dark: they emit short ultrasonic vibrations that bounce back after hitting some matter. Differences in the received echoes indicate them where the potential prey is.
: echography
Like the sonar system, in echographies an ultrasound device is used to generate and receive hundreds of high frequency soundwaves that cannot be perceived by the human ear. These waves are momentarily absorbed by the human tissues, bones and body fluids [all of them with different densities] and then bounce back to create an ultrasound image very much like a negative picture; black areas indicate liquid media [like amniotic fluid] and grey or white indicate higher density areas, like tissues or bones.
Ultrasound frequencies are measured in Megahertz and usually range from 3 to 7.5 MHz. Like in electro·magnetic radiation, the lower the frequency, the farther [or deeper] the soundwaves can penetrate body tissues.
Nowadays the ultrasound technique has been improved to the point of even producing colour or 3d images.