X-ray photons are highly energetic and have enough energy to break up molecules and hence damage living cells. Table 1 Energy carried by each photonFrequency of electromagnetic wave (Hz)Wavelength (pm, 1pm = 10 -12 m)Thickness of material to halve number of photons (half value thickness) (mm)in electron-volts (eV)in joules (J)ConcreteLeadHuman tissueAluminium1keV1.602 × 10 -16 2.418 × 10 17 12400.00090.000120.00180.002210keV1.602 × 10 -15 2.418 × 10 18 1240.1470.0471.220.098100keV1.602 × 10 -14 2.418 × 10 19 12.417.30.11038.615.11MeV1.602 × 10 -13 2.418 × 10 20 1.2446.48.6093.341.810MeV1.602 × 10 -12 2.418 × 10 21 0.12413212.3298111 X-rays are highly penetrating and interact with matter through ionization via three processes, photoelectric effect, Compton scattering or pair production.
Due to their high penetration power the impact of X-rays can occur throughout a body, they are however less ionizing than alpha particles. X-rays are commonly produced in X-ray tubes by accelerating electrons through a potential difference (a voltage drop) and directing them onto a target material (i.e. tungsten).
A computed tomography (CT) scanner is a particular type of X-ray machine in which the X-ray tube produces a beam in the shape of a fan and moves around the patient in a circle. The X-rays are detected electronically and a computer uses the information to reconstruct an image of the region of the body exposed.
A synchrotron is a device that accelerates electrons in an evacuated ring (often several tens of meters in diameter), steering them with magnets. Industrial radiography can use X-ray or gamma sources for analysis to look for cracks in buildings, structures or pressure vessels.
A diagnostic X-ray should be performed to provide information that helps medical staff treat a patient’s condition appropriately. In general, this information is much more important to a person’s health than the small estimated risk (typically less than 0.01%) of the chance of developing cancer from the procedure.
Modern X-ray equipment has many features that if used properly can limit the area irradiated and the dose delivered to the minimum necessary for obtaining the diagnostic information. Unlike light, however, x-rays have higher energy and can pass through most objects, including the body.
To create a radiograph, a patient is positioned so that the part of the body being imaged is located between an x-ray source and an x-ray detector. Conversely, x-rays travel more easily through less radiologically dense tissues such as fat and muscle, as well as through air-filled cavities such as the lungs.
X-ray radiography: Detects bone fractures, certain tumors and other abnormal masses, pneumonia, some types of injuries, calcifications, foreign objects, dental problems, etc. CT's images are more detailed than plain radiographs and give doctors the ability to view structures within the body from many angles.
Fluoroscopy: Uses x-rays and a fluorescent screen to obtain real-time images of movement within the body or to view diagnostic processes, such as following the path of an injected or swallowed contrast agent. This technology is also used with a radiographic contrast agent to guide an internally threaded catheter during cardiac angioplasty, which is a minimally invasive procedure for opening clogged arteries that supply blood to the heart.
X-ray scans can diagnose possibly life-threatening conditions such as blocked blood vessels, bone cancer, and infections. An x-ray in a pregnant woman poses no known risks to the baby if the area of the body being imaged isn’t the abdomen or pelvis.
In general, if imaging of the abdomen and pelvis is needed, doctors prefer to use exams that do not use radiation, such as MRI or ultrasound. However, if neither of those can provide the answers needed, or there is an emergency or other time constraint, an x-ray may be an acceptable alternative imaging option.
Children are more sensitive to ionizing radiation and have a longer life expectancy and, thus, a higher relative risk for developing cancer than adults. Current research of x-ray technology focuses on ways to reduce radiation dose, improve image resolution, and enhance contrast materials and methods.
For detailed examples of research advancements for specific imaging procedures, click on the links below: Illustration of the relative abilities of three different types of ionizing radiation to penetrate solid matter.
The international symbol for types and levels of radiation that are unsafe for shielded humans. Other sources include X-rays from medical radiography examinations and muons, mesons, positrons, neutrons and other particles that constitute the secondary cosmic rays that are produced after primary cosmic rays interact with Earth's atmosphere.
Gamma rays, X-rays and the higher energy range of ultraviolet light constitute the ionizing part of the electromagnetic spectrum. The word “ionize” refers to the breaking of one or more electrons away from an atom, an action that requires the relatively high energies that these electromagnetic waves supply.
Further down the spectrum, the non-ionizing lower energies of the lower ultraviolet spectrum cannot ionize atoms, but can disrupt the inter-atomic bonds which form molecules, thereby breaking down molecules rather than atoms; a good example of this is sunburn caused by long- wavelength solar ultraviolet. This aspect leads to a system of measurements and physical units that are applicable to all types of radiation.
While an individual cell is made of trillions of atoms, only a small fraction of those will be ionized at low to moderate radiation powers. Particle radiation from radioactive material or cosmic rays almost invariably carries enough energy to be ionizing.
Exposure to radiation causes damage to living tissue; high doses result in Acute radiation syndrome (AS), with skin burns, hair loss, internal organ failure and death, while any dose may result in an increased chance of cancer and genetic damage ; a particular form of cancer, thyroid cancer, often occurs when nuclear weapons and reactors are the radiation source because of the biological proclivities of the radioactive iodine fission product, iodine-131. However, calculating the exact risk and chance of cancer forming in cells caused by ionizing radiation is still not well understood and currently estimates are loosely determined by population based data from the atomic bombings of Hiroshima and Nagasaki and from follow-up of reactor accidents, such as the Chernobyl disaster.
The International Commission on Radiological Protection states that “The Commission is aware of uncertainties and lack of precision of the models and parameter values”, “Collective effective dose is not intended as a tool for epidemiological risk assessment, and it is inappropriate to use it in risk projections” and “in particular, the calculation of the number of cancer deaths based on collective effective doses from trivial individual doses should be avoided.” Ionizing UV therefore does not penetrate Earth's atmosphere to a significant degree, and is sometimes referred to as vacuum ultraviolet.
Although present in space, this part of the UV spectrum is not of biological importance, because it does not reach living organisms on Earth. Some of the ultraviolet spectrum that does reach the ground is non-ionizing, but is still biologically hazardous due to the ability of single photons of this energy to cause electronic excitation in biological molecules, and thus damage them by means of unwanted reactions.
An example is the formation of pyrimidine divers in DNA, which begins at wavelengths below 365 nm (3.4 eV), which is well below ionization energy. This property gives the ultraviolet spectrum some dangers of ionizing radiation in biological systems without actual ionization occurring.
In contrast, visible light and longer-wavelength electromagnetic radiation, such as infrared, microwaves, and radio waves, consists of photons with too little energy to cause damaging molecular excitation, and thus this radiation is far less hazardous per unit of energy. A smaller wavelength corresponds to a higher energy according to the equation E = HC / .
Generally, larger atoms are more likely to absorb an X-ray photon since they have greater energy differences between orbital electrons. X-ray machines are specifically designed to take advantage of the absorption difference between bone and soft tissue, allowing physicians to examine structure in the human body.
X-rays are also totally absorbed by the thickness of the earth's atmosphere, resulting in the prevention of the X-ray output of the sun, smaller in quantity than that of UV but nonetheless powerful, from reaching the surface. Gamma () radiation consists of photons with a wavelength less than 3×10 11 meters (greater than 10 19 Hz and 41.4 key).
Both alpha and beta particles have an electric charge and mass, and thus are quite likely to interact with other atoms in their path. However, as is the case with X-rays, materials with high atomic number such as lead or depleted uranium add a modest (typically 20% to 30%) amount of stopping power over an equal mass of less dense and lower atomic weight materials (such as water or concrete).
Even air is capable of absorbing gamma rays, halving the energy of such waves by passing through, on the average, 500 ft (150 m). They interact with matter strongly due to their charges and combined mass, and at their usual velocities only penetrate a few centimeters of air, or a few millimeters of low density material (such as the thin mica material which is specially placed in some Geiger counter tubes to allow alpha particles in).
Some very high energy alpha particles compose about 10% of cosmic rays, and these are capable of penetrating the body and even thin metal plates. This brings the radioisotope close enough to sensitive live tissue for the alpha radiation to damage cells.
Per unit of energy, alpha particles are at least 20 times more effective at cell-damage as gamma rays and X-rays. Examples of highly poisonous alpha-emitters are all isotopes of radium, radon, and polonium, due to the amount of decay that occur in these short half-life materials.
Beta radiation from radioactive decay can be stopped with a few centimeters of plastic or a few millimeters of metal. It occurs when a neutron decays into a proton in a nucleus, releasing the beta particle and an antineutrino.
The gamma radiation from positron annihilation consists of high energy photons, and is also ionizing. Neutrons are rare radiation particles; they are produced in large numbers only where chain reaction fission or fusion reactions are active; this happens for about 10 microseconds in a thermonuclear explosion, or continuously inside an operating nuclear reactor; production of the neutrons stops almost immediately in the reactor when it goes non-critical.
This process, called neutron activation, is the primary method used to produce radioactive sources for use in medical, academic, and industrial applications. Not all materials are capable of neutron activation; in water, for example, the most common isotopes of both types atoms present (hydrogen and oxygen) capture neutrons and become heavier but remain stable forms of those atoms.
The sodium in salt (as in seawater), on the other hand, need only absorb a single neutron to become Na-24, a very intense source of beta decay, with half-life of 15 hours. They typically require hydrogen rich shielding, such as concrete or water, to block them within distances of less than a meter.
A common source of neutron radiation occurs inside a nuclear reactor, where a meters-thick water layer is used as effective shielding. The sun continuously emits particles, primarily free protons, in the solar wind, and occasionally augments the flow hugely with coronal mass ejections (CME).
The origin of these galactic cosmic rays is not yet well understood, but they seem to be remnants of supernovae and especially gamma-ray bursts (GB), which feature magnetic fields capable of the huge accelerations measured from these particles. They may also be generated by quasars, which are galaxy-wide jet phenomena similar to Grabs but known for their much larger size, and which seem to be a violent part of the universe's early history.
The kinetic energy of particles of non-ionizing radiation is too small to produce charged ions when passing through matter. For non-ionizing electromagnetic radiation (see types below), the associated particles (photons) have only sufficient energy to change the rotational, vibrational or electronic valence configurations of molecules and atoms.
Even “non-ionizing” radiation is capable of causing thermal-ionization if it deposits enough heat to raise temperatures to ionization energies. The lower frequencies of ultraviolet light may cause chemical changes and molecular damage similar to ionization, but is technically not ionizing.
The occurrence of ionization depends on the energy of the 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, unless they raise the temperature of a body to a point high enough to ionize small fractions of atoms or molecules by the process of thermal-ionization (this, however, requires relatively extreme radiation intensities).
More broadly, physicists use the term “light” to mean electromagnetic radiation of all wavelengths, whether visible or not. Infrared (IR) light is electromagnetic radiation with a wavelength between 0.7 and 300 micrometers, which corresponds to a frequency range between 430 and 1 The respectively.
This broad definition includes both UHF and EHF (millimeter waves), but various sources use different other limits. In addition, almost any wire carrying alternating current will radiate some energy away as radio waves; these are mostly termed interference.
In the related magnetosphere science, the lower frequency electromagnetic oscillations (pulsations occurring below ~3 Hz) are considered to lie in the UHF range, which is thus also defined differently from the ITU Radio Bands. A massive military ELF antenna in Michigan radiates very slow messages to otherwise unreachable receivers, such as submerged submarines.
The frequency at which the black-body radiation is at maximum is given by Wain's displacement law and is a function of the body's absolute temperature. It is responsible for the color of stars, which vary from infrared through red (2,500K), to yellow (5,800K), to white and to blue-white (15,000K) as the peak radiance passes through those points in the visible spectrum.
Herschel, like Ritter, used a prism to refract light from the Sun and detected the infrared (beyond the red part of the spectrum), through an increase in the temperature recorded by a thermometer. In 1801, the German physicist Johann Wilhelm Ritter made the discovery of ultraviolet by noting that the rays from a prism darkened silver chloride preparations more quickly than violet light.
Ritter noted that the UV rays were capable of causing chemical reactions. The first radio waves detected were not from a natural source, but were produced deliberately and artificially by the German scientist Heinrich Hertz in 1887, using electrical circuits calculated to produce oscillations in the radio frequency range, following formulas suggested by the equations of James Clerk Maxwell.
While experimenting with high voltages applied to an evacuated tube on 8 November 1895, he noticed a fluorescence on a nearby plate of coated glass. In 1896, Henri Becquerel found that rays emanating from certain minerals penetrated black paper and caused fogging of an unexposed photographic plate.
His doctoral student Marie Curie discovered that only certain chemical elements gave off these rays of energy. One type had short penetration (it was stopped by paper) and a positive charge, which Rutherford named alpha rays.
The other was more penetrating (able to expose film through paper but not metal) and had a negative charge, and this type Rutherford named beta. In 1900, the French scientist Paul Willard discovered a third neutrally charged and especially penetrating type of radiation from radium, and after he described it, Rutherford realized it must be yet a third type of radiation, which in 1903 Rutherford named gamma rays.
Cosmic ray radiations striking the Earth from outer space were finally definitively recognized and proven to exist in 1912, as the scientist Victor Hess carried an electrometer to various altitudes in a free balloon flight. A number of other high energy particulate radiations such as positrons, muons, and ions were discovered by cloud chamber examination of cosmic ray reactions shortly thereafter, and others types of particle radiation were produced artificially in particle accelerators, through the last half of the twentieth century.
This property of X-rays enables doctors to find broken bones and to locate cancers that might be growing in the body. Variations in the intensity of the radiation represent changes in the sound, pictures, or other information being transmitted.
Musicians have also experimented with gamma rays modification, or using nuclear radiation, to produce sound and music. Researchers use radioactive atoms to determine the age of materials that were once part of a living organism.
The age of such materials can be estimated by measuring the amount of radioactive carbon they contain in a process called radiocarbon dating. Similarly, using other radioactive elements, the age of rocks and other geological features (even some man-made objects) can be determined; this is called Radiometric dating.
Radiation is used to determine the composition of materials in a process called neutron activation analysis. In this process, scientists bombard a sample of a substance with particles called neutrons.
In 2011, the International Agency for Research on Cancer (ARC) of the World Health Organization (WHO) released a statement adding radio frequency electromagnetic fields (including microwave and millimeter waves) to their list of things which are possibly carcinogenic to humans. RWTH Aachen University's EMF-Portal website presents one of the biggest database about the effects of Electromagnetic radiation.
As of 12 July 2019 it has 28,547 publications and 6,369 summaries of individual scientific studies on the effects of electromagnetic fields.