X-Ray Radiation
X-ray radiation is a form of electromagnetic radiation that occupies a specific segment of the electromagnetic spectrum with wavelengths ranging from 0.1 to 10 nanometers. This positions X-rays between gamma rays, which have even shorter wavelengths, and ultraviolet light, which has longer wavelengths. X-rays are produced both naturally, through sources like some radioactive elements and cosmic phenomena, and artificially, via devices such as x-ray tubes, where processes like bremsstrahlung generate the radiation.
X-rays are classified as ionizing radiation, which means they possess enough energy to dislodge electrons from atoms, potentially leading to cellular changes and increasing the risk of cancer with sufficient exposure. In medical settings, X-rays are valuable for imaging purposes, as they can penetrate soft tissues while being absorbed by denser materials like bone. To mitigate potential DNA damage during procedures, patients often wear protective lead aprons.
In addition to medical applications, X-rays are also utilized in various scientific fields to analyze materials and study the universe. Understanding phenomena such as Compton scattering and Rayleigh scattering highlights the intricate behaviors of X-rays when interacting with matter, further illustrating their complexity and significance in both health and science.
X-Ray Radiation
FIELDS OF STUDY: Electromagnetism; Atomic Physics; Nuclear Physics
ABSTRACT: X-ray radiation is a type of electromagnetic radiation with a wavelength between 0.1 and 10 nanometers. It falls between gamma rays (shorter wavelength, more energy) and ultraviolet rays (longer wavelength, less energy) on the electromagnetic spectrum. X-rays occur naturally both on Earth and in space. Artificially created x-rays are useful in physics and medicine, among other fields.
PRINCIPAL TERMS
- bremsstrahlung: the electromagnetic radiation released by charged subatomic particles when they hit another charged particle; the momentum lost in the collision is converted into energy transmitted as radiation.
- Compton scattering: the phenomenon that when electromagnetic radiation of very short wavelength (such as x-rays or gamma rays) hits an electron, it behaves like a particle hitting another particle and is deflected at an angle, which changes the wavelength of the radiation after the interaction.
- electromagnetic spectrum: the full range of electromagnetic radiation, sorted into segments with similar properties by wavelength; x-rays occupy one of these segments.
- non-ionizing radiation: electromagnetic radiation that lacks the energy necessary to knock electrons free when it hits an atom; all types of electromagnetic radiation with a longer wavelength (less energy) than ultraviolet is non-ionizing.
- photoabsorption: the absorption of the energy of electromagnetic radiation into matter; different substances absorb radiation at different rates.
- Rayleigh scattering: the scattering of electromagnetic radiation when it encounters particles much smaller than the radiation’s wavelength, as, for example, the scattering of visible light in the atmosphere.
- wavelength: the distance between crests (or troughs) of a wave; the length of one complete cycle. Longer wavelengths correspond to lower frequencies and less energy, and vice versa.
- revolution: describes circular motion wherein an object circles an internal axis (e.g. the moon spinning about its axis); contrast to rotation, wherein the axis is external (e.g. the moon orbiting the earth).
X-Rays and the Electromagnetic Spectrum
Every type of electromagnetic radiation (EMR) is categorized on the electromagnetic (EM) spectrum by wavelength. Wavelength—the distance between two peaks or two troughs of a wave—is inversely proportional to the frequency of and energy transmitted by the wave. The EM spectrum is arranged from short wavelengths (high frequency or energy) to very long wavelengths (low frequency or energy). X-ray light falls between gamma radiation and ultraviolet light on the EM spectrum.
Gamma radiation has a wavelength of less than 0.01 nanometers. (One nanometer is 1 × 10−9 meters.) It comes from gamma decay, a type of radioactive decay. In gamma decay, a high-energy particle called a photon is ejected from the nucleus of an atom.
X-rays have wavelengths between 0.1 and 10 nanometers. High-energy, short-wavelength x-rays are called "hard x-rays." These belong to the same part of the EM spectrum as gamma rays but come from electrons, not atomic nuclei. X-rays are naturally produced by some radioactive elements, radon gas, and superhot gases in space. They are also created by devices like x-ray vacuum tubes.
Ultraviolet (UV) radiation has wavelengths of 10 to 400 nanometers. The most familiar source of UV rays is the sun. UV rays can cause skin to tan, burn, or even develop cancer.
The longer-wavelength forms of EMR include visible light (comprising the colors seen by the human eye), infrared, radio and microwaves, and longwave radiation.
Ionizing versus Non-Ionizing Radiation
X-rays and gamma rays are often what come to mind when people talk about the dangers of radiation exposure. Both are types of ionizing radiation. Indeed, UV light and all higher-energy EMR is ionizing. This means it has enough energy that when it strikes an atom, it can knock electrons loose, altering the way the atom interacts with other nearby atoms. If ionizing radiation penetrates DNA, it can cause errors in cell replication that lead to cancer. Therefore, all ionizing radiation can cause cancer with enough exposure, though the risk varies greatly by type of radiation and type of exposure. Non-ionizing radiation—EMR with wavelengths longer than ultraviolet—can still be dangerous (for instance, infrared can cause burns), but it will not alter DNA structure.
Medical X-Rays
X-rays have short enough wavelengths to pass through many types of matter without much distortion yet can interact with certain materials, making them useful tools for probing the unseen. Photoabsorption refers to the transfer of energy from EMR photons to the electrons in a material upon impact. Bone has a higher photoabsorption rate than skin and soft tissues do. Thus, x-rays pass through the human body mostly unobstructed except when they hit bone or other calcium-heavy areas. This is how medical x-rays work. To protect sensitive tissues from DNA damage, patients wear lead-lined aprons during medical x-ray scans because lead is impervious to x-rays.
X-rays of the kind used in x-ray machines are often produced by an x-ray tube, which uses the phenomenon of bremsstrahlung to generate the radiation. Bremsstrahlung, "braking radiation" in German, is the radiation released when charged subatomic particles like electrons slow down quickly after contact with atomic nuclei. X-ray tubes use electric fields to fire electrons into a metal at high speed, causing bremsstrahlung x-rays to be emitted.
X-Rays and the Subatomic World
Two important types of scattering may occur when x-rays encounter subatomic particles like those in the atmosphere. Rayleigh scattering occurs when EMR encounters particles much smaller than its wavelength, causing it to change course without losing energy or being absorbed. It is not a significant obstacle to x-rays due to x-rays’ short wavelengths. Compton scattering occurs when x-rays hit an electron. The electron is knocked free of its atom, and the x-ray loses a photon of energy and its wavelength increases. The discovery and description of Compton scattering using x-rays by American physicist Arthur H. Compton (1892–1962) in the 1920s proved that EMR can behave like a particle as well as a wave. This wave-particle duality of EMR is key to modern quantum mechanics, a branch of physics that studies subatomic particles.
Uses of X-Rays
X-rays are present in the cosmic rays that hit Earth from space, generated by super-hot gases like those in the sun. Sources of x-rays are relatively rare on Earth, though they can be produced by radioactive elements and radon gas. Most often, the x-rays that humans encounter come from humanmade devices like x-ray tubes used in medical detection or targeted cancer treatment or scanners used for airport security checkpoints. Scientists also use x-rays to study the chemical makeup of materials from crystals to stars and other celestial bodies.
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