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  1. #1

    Default Περί ακτινοβολίας

    Electromagnetic Radiation
    Main article: Electromagnetic Radiation

    Electromagnetic radiation (sometimes abbreviated EMR) takes the form of self-propagating waves in a vacuum or in matter. EM radiation has an electric and magnetic field component which oscillate in phase perpendicular to each other and to the direction of energy propagation. Electromagnetic radiation is classified into types according to the frequency of the wave, these types include (in order of increasing frequency): radio waves, microwaves, terahertz radiation, infrared radiation, visible light, ultraviolet radiation, X-rays and gamma rays. Of these, radio waves have the longest wavelengths and Gamma rays have the shortest. A small window of frequencies, called visible spectrum or light, is sensed by the eye of various organisms, with variations of the limits of this narrow spectrum. EM radiation carries energy and momentum, which may be imparted when it interacts with matter.
    http://en.wikipedia.org/wiki/Radiati...etic_Radiation


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  2. #2

    Default από τα Βοροσιλικάτα με αγάπη

    Radioactive decay
    Radioactive decay is the process in which an unstable atomic nucleus spontaneously loses energy by emitting ionizing particles and radiation. This decay, or loss of energy, results in an atom of one type, called the parent nuclide transforming to an atom of a different type, named the daughter nuclide. For example: a carbon-14 atom (the "parent") emits radiation and transforms to a nitrogen-14 atom (the "daughter"). This is a stochastic process on the atomic level, in that it is impossible to predict when a given atom will decay, but given a large number of similar atoms the decay rate, on average, is predictable.
    http://en.wikipedia.org/wiki/Radioactive_decay

    Particle decay is the spontaneous process of one elementary particle transforming into other elementary particles. During this process, an elementary particle becomes a different particle with less mass and an intermediate particle such as W boson in muon decay. The intermediate particle then transforms into other particles. If the particles created are not stable, the decay process can continue.

    The process of particle decay is distinct from radioactive decay, in which an unstable atomic nucleus is transformed into a smaller nucleus accompanied by the emission of particles or radiation.
    http://en.wikipedia.org/wiki/Particle_decay



    Tritium illumination is the use of gaseous tritium, a radioactive isotope of hydrogen, to create visible light. Tritium regularly emits electrons through beta decay, and when they interact with a phosphor material, fluorescent light is created.
    http://en.wikipedia.org/wiki/Self-powered_lighting

    The tritium in a gaseous tritium light source undergoes beta decay, releasing electrons which cause the phosphor layer to fluoresce.

    During manufacture, a length of borosilicate glass tube which has had the inside surface coated with a phosphor-containing material is filled with the radioactive tritium. The tube is then fused with a CO2 laser at the desired length. Borosilicate is preferred because it is a type of glass noted for its strength and resistance to breakage. In the tube, the tritium gives off a steady stream of electrons due to beta decay. These particles excite the phosphor, causing it to emit a low, steady glow. One could use any beta particle-emitting substance, but in practice tritium is preferred because it is not very hazardous.
    http://en.wikipedia.org/wiki/Self-po...hind_the_light

  3. #3

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    In physics, radiation describes any process in which energy emitted by one body travels through a medium or through space, ultimately to be absorbed by another body. Non-physicists often associate the word with ionizing radiation (e.g., as occurring in nuclear weapons, nuclear reactors, and radioactive substances), but it can also refer to electromagnetic radiation (i.e., radio waves, infrared light, visible light, ultraviolet light, and X-rays) which can also be ionizing radiation,
    http://en.wikipedia.org/wiki/Radiati...etic_Radiation



    Ionizing radiation consists of subatomic particles or electromagnetic waves that are energetic enough to detach electrons from atoms or molecules, ionizing them. The occurrence of ionization depends on the energy of the impinging individual particles or waves, and not on their number. An intense flood of particles or waves will not cause ionization if these particles or waves do not carry enough energy to be ionizing. Roughly speaking, particles or photons with energies above a few electron volts (eV) are ionizing.

    Examples of ionizing particles are energetic alpha particles, beta particles, and neutrons. The ability of electromagnetic waves (photons) to ionize an atom or molecule depends on their wavelength. Radiation on the short wavelength end of the electromagnetic spectrum — ultraviolet, x-rays, and gamma rays — is ionizing.

    Ionizing radiation comes from radioactive materials, x-ray tubes, particle accelerators, and is present in the environment. It is invisible and not directly detectable by human senses, so instruments such as geiger counters are usually required to detect its presence. In some cases it may lead to secondary emission of visible light upon interaction with matter, as in Cherenkov radiation and radioluminescence. It has many practical uses in medicine, research, construction, and other areas, but presents a health hazard if used improperly. Exposure to radiation causes damage to living tissue, resulting in skin burns, radiation sickness and death at high doses and cancer,[2] tumors and genetic damage at low doses.
    http://en.wikipedia.org/wiki/Ionizing_radiation

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  4. #4

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    Δεν υπάρχει λόγος ανησυχίας, δεν παλάβωσα (όχι περισσότερο δηλαδή...) απλά κάτι λέγαμε χθες με το Δημήτρη και τα άλλα παιδιά και με τις μπύρες στο χέρι και είπα να ρίξω και κανένα link για το αρχείο.



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  5. #5

    Default

    Α και για να μην ξεχαστούμε:


    Electromagnetic Radiation
    Main article: Electromagnetic Radiation
    Electromagnetic radiation (sometimes abbreviated EMR) takes the form of self-propagating waves in a vacuum or in matter. EM radiation has an electric and magnetic field component which oscillate in phase perpendicular to each other and to the direction of energy propagation. Electromagnetic radiation is classified into types according to the frequency of the wave, these types include (in order of increasing frequency): radio waves, microwaves, terahertz radiation, infrared radiation, visible light, ultraviolet radiation, X-rays and gamma rays. Of these, radio waves have the longest wavelengths and Gamma rays have the shortest. A small window of frequencies, called visible spectrum or light, is sensed by the eye of various organisms, with variations of the limits of this narrow spectrum. EM radiation carries energy and momentum, which may be imparted when it interacts with matter.
    http://en.wikipedia.org/wiki/Radiati...etic_Radiation


    Electromagnetic radiation (sometimes abbreviated EMR) is a ubiquitous phenomenon that takes the form of self-propagating waves in a vacuum or in matter. It consists of electric and magnetic field components which oscillate in phase perpendicular to each other and perpendicular to the direction of energy propagation. Electromagnetic radiation is classified into several types according to the frequency of its wave; these types include (in order of increasing frequency and decreasing wavelength): radio waves, microwaves, terahertz radiation, infrared radiation, visible light, ultraviolet radiation, X-rays and gamma rays. A small and somewhat variable window of frequencies is sensed by the eyes of various organisms; this is what we call the visible spectrum, or light.

    EM radiation carries energy and momentum that may be imparted to matter with which it interacts.
    http://en.wikipedia.org/wiki/Electromagnetic_Radiation



    EM radiation exhibits both wave properties and particle properties at the same time (see wave-particle duality). Both wave and particle characteristics have been confirmed in a large number of experiments. Wave characteristics are more apparent when EM radiation is measured over relatively large timescales and over large distances while particle characteristics are more evident when measuring small timescales and distances. For example, when electromagnetic radiation is absorbed by matter, particle-like properties will be more obvious when the average number of photons in the cube of the relevant wavelength is much smaller than 1. Upon absorption the quantum nature of the light leads to clearly non-uniform deposition of energy.
    http://en.wikipedia.org/wiki/Electro...ion#Properties


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    Last edited by Vassilis; 10-03-2009 at 09:31 AM.

  6. #6

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    Electromagnetic shielding

    How RF shielding workshttp://en.wikipedia.org/wiki/Electro...hielding_works

    Faraday cage
    The metal layers are grounded to dissipate any electric currents generated from the external electromagnetic fields, and thus block a large amount of the electromagnetic interference.
    http://en.wikipedia.org/wiki/Faraday_cage

    Magnetic shielding
    Equipment sometimes requires isolation from external magnetic fields. For static or slowly varying magnetic fields (below about 100 kHz) the Faraday shielding described above is ineffective. There exists a limited possibility of passively isolating a volume magnetically by using shields made of high magnetic permeability metal alloys such as Permalloy and Mu-metal[1]. These materials don't block the magnetic field, as with electric shielding, but rather draw the field into themselves, providing a path for the magnetic field lines around the shielded volume. The best shape for magnetic shields is thus a closed container
    http://en.wikipedia.org/wiki/Electro...etic_shielding


    Paramagnetism
    Paramagnetism is a form of magnetism which occurs only in the presence of an externally applied magnetic field. Paramagnetic materials are attracted to magnetic fields, hence have a relative magnetic permeability greater than one (or, equivalently, a positive magnetic susceptibility). The magnetic moment induced by the applied field is linear in the field strength and rather weak. It typically requires a sensitive analytical balance to detect the effect. Unlike ferromagnets, paramagnets do not retain any magnetization in the absence of an externally applied magnetic field, because thermal motion causes the spins to become randomly oriented without it. Thus the total magnetization will drop to zero when the applied field is removed. Even in the presence of the field there is only a small induced magnetization because only a small fraction of the spins will be oriented by the field. This fraction is proportional to the field strength and this explains the linear dependency.
    http://en.wikipedia.org/wiki/Magneti...#Paramagnetism

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