| Non-thermal electromagnetic radiation is used almost exclusively by humans in the telecommunications and entertainment industries. All non-thermal emissions are generated electronically by oscillating electrons in conductors by modulating the voltage applied to a length of wire.
The frequency of the radiation is usually controlled by taking advantage of the natural oscillating frequencies of "tuned" circuits or quartz crystals. This method is used for generating all types of electromagnetic radiation, from microwave ovens to radar, and from TV signals to garage door openers. The environment in which we live is literally filled with the artificially generated non-thermal electromagnetic radiation from tens of thousands of transmitters around the world. These range from local cell phone signals to multichannel TV signals beamed down from geostationary satellites. If our eyes were able to detect radio waves, we would probably be blinded by the brilliance of our surroundings in every direction, in every place, day and night! The Earth is nearly a million times brighter than the Sun at radio wavelengths. This is because the Sun is mainly a thermal source of electromagnetic radiation and most of its radiation is in the visible part of the spectrum. On Earth we have learned how to build intense sources of non-thermal radiation. |
| Non-thermal electromagnetic X-ray radiation is widely used for medical as well as industrial applications. |
| A simple device to generate X-rays | X-rays are easily generated by accelerating a beam of electrons through a high voltage gradient and then colliding them into a metal plate as shown in the sketch to the left.
The X-rays that emerge have a range of energies, however the maximum energy (i.e. the shortest wavelength) is determined entirely by the voltage difference through which the beam of electrons is accelerated. For example a beam of electrons accelerated through a potential difference of 50keV, will produce X-rays photons up to but never exceeding 50keV. |
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| A major fraction of the energy in the electron beam is converted to heat in the anode, therefore high energy X-ray tubes are often water cooled to dissipate the excess heat. |
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The penetrating power of X-rays makes them ideal for medical diagnostics. However, X-ray photons have energies which can cause ionization and therefore are biologically hazardous if the absorbed dose is not kept below recommended minimums.
X-rays cannot be seen, but when they collide with atoms of phosphorous compounds embedded in a glass plate, the electrons in the compound are raised to higher energy levels causing the phosphorous plate to glow, the dark regions being zones of high X-ray absorption i.e. this forms a positive image. Alternately, the glass plate can be replaced by a photographic plate. The transmitted X-ray photons "expose" the film in the same way that light exposes an ordinary photograph. In this case, the regions of high X-ray absorption leave the film unexposed and they appear white on the film i.e. it is a negative image. |
| It is well known that cancer cells multiply rapidly because the genetic coding that regulates the cell's metabolic and reproductive processes has become scrambled. But, this scrambled genetic coding has also degraded the cell's ability to repair itself in the face of molecular damage.
Cancer treatments have been developed to take advantage of the cancer cell's degraded resistance to slight molecular damage. All methods utilize ionizing radiation. It is possible to "deliver" the ionizing radiation to the cancer site in many ways:
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Radio-isotopes are created by subjecting samples of various elements to the intense neutron flux
inside the core of a nuclear reactor. As the element gets bombarded by low energy neutrons, the nucleus of the element "catches" and holds (an) extra neutron in its nucleus. In this state the nucleus of the element is unstable...it has become a radioactive isotope..or radio-isotope for short. The radio-isotope can be chemically separated from the irradiated sample, concentrated, and shipped to the appropriate medical facility for therapeutic use. The radio-isotopes have such short half-lives that they must be used within hours of their delivery, otherwise they are useless. In a therapeutic "cocktail" the radio-isotope is chemically incorporated into a soluble molecule for which the targeted part of the body has a chemical affinity. The molecule is then easily absorbed into the blood stream and then deposited at the selected site in the body. The particle and electromagnetic radiation from the ingested isotope create slight cellular damage to both cancerous and normal cells. The normal cells quickly and easily repair themselves, whereas the absorbed dose is fatal to the less metabolically and genetically robust cancer cells. |
| Considerable concern has been expressed about the virtues and vices of nuclear power generation. Like most high-profile public debates, there is certainly no shortage of option.
The concerns generally centre on problems related to the accidental release of radioactive agents into the atmosphere and the long term storage of "spent" nuclear fuel. The fundamental question is essentially one of risk, "how much risk is acceptable?" and "how are the risks of nuclear power generation to be evaluated with respect to all other forms of personal and environmental risk that we conventionally accept without concern?" It is the particle and gamma ray emissions from radioactive isotopes (that are created by the nuclear industry) that have the potential to increase the absorbed radiation dose to which humans are exposed. Under normal conditions, and in a wide range of abnormal conditons, the threat of exposure by individuals, and the public in general, is extraordinarily low. The radioactive isotopes are created in serveral ways
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