Draft:Original research/Radiation

Radiation is an action or process of throwing or sending out a traveling ray in a line, beam, or stream of small relative cross section.

At right is an image of an impact crater on the surface of Venus. It is a likely example of meteor radiation damage.

Rays
Def. a beam of light or radiation is called a ray.

Def. an action or process of throwing or sending out a traveling ray in a line, beam, or stream of small cross section is called radiation.

The term radiation is often used to refer to the ray itself.

Def. the shooting forth of anything from a point or surface, like the diverging rays of light; as, the radiation of heat is called radiation.

Rays may have a temporal, spectral, or spatial distribution.

They may also be dependent on other variables as yet unknown.

A delta ray is characterized by very fast electrons produced in quantity by alpha particles or other fast energetic charged particles knocking orbiting electrons out of atoms. Collectively, these electrons are defined as delta radiation when they have sufficient energy to ionize further atoms through subsequent interactions on their own.

Epsilon radiation is tertiary radiation caused by secondary radiation (e.g., delta radiation). Epsilon rays are a form of particle radiation and are composed of electrons. The term is very rarely used today.

Radiation theory
Def. a theory of the science of the biological, chemical, physical, and logical laws (or principles) with respect to any radiation is called a theory of radiation.

Particle radiation consists of a stream of charged or neutral particles, from the size of subatomic elementary particles upwards of rocky and gaseous objects to even larger more loosely bound entities.

Strong forces
A "new type of neutron star model (Q stars) [is such that] high-density, electrically neutral baryonic matter is a coherent classical solution to an effective field theory of strong forces and is bound in the absence of gravity. [...] allows massive compact objects, [...] and has no macroscopic minimum mass."

"Compact objects in astronomy are usually analyzed in terms of theoretical characteristics of neutron stars or black holes that are based upon calculations of equations of state for matter at very high densities. At such high densities, the effects of strong forces cannot be neglected. There are several conventional approaches to describing nuclear forces, all of which find that for a baryon number greater than ~250, a nucleus will become energetically unbound. High-density hadronic matter is not stable in these theories until there are enough baryons for gravitational binding to form a neutron star, typically with a minimum mass ≳ 0.1 M⊙ and maximum mass ≲ 3 M⊙."

"Another possibility [called "baryon matter"] is that in the absence of gravity high-density baryonic matter is bound by purely strong forces. [...] nongravitationally bound bulk hadronic matter is consistent with nuclear physics data [...] and low-energy strong interaction data [...] The effective field theory approach has many successes in nuclear physics [...] suggesting that bulk hadronic matter is just as likely to be a correct description of matter at high densities as conventional, unbound hadronic matter."

"The idea behind baryon matter is that a macroscopic state may exist in which a smaller effective baryon mass inside some region makes the state energetically favored over free particles. [...] This state will appear in the limit of large baryon number as an electrically neutral coherent bound state of neutrons, protons, and electrons in β-decay equilibrium."

Meteors
Particle radiation upwards in size above that of atomic nuclei may be lumped together as meteor radiation.

Galaxy clusters
"Galaxies and clusters of galaxies are not uniformly distributed in the Universe, instead they collect into vast clusters and sheets and walls of galaxies interspersed with large voids in which very few galaxies seem to exist. The map above shows many of these superclusters including the Virgo supercluster - the minor supercluster of which our galaxy is just a minor member. The entire map is approximately 7 percent of the diameter of the entire visible Universe."

High-velocity galaxies
"The irregular galaxy NGC 1427A is a spectacular example of the resulting stellar rumble. Under the gravitational grasp of a large gang of galaxies, called the Fornax cluster, the small bluish galaxy is plunging headlong into the group at 600 kilometers per second or nearly 400 miles per second."

"Galaxy clusters, like the Fornax cluster, contain hundreds or even thousands of individual galaxies. Within the Fornax cluster, there is a considerable amount of gas lying between the galaxies. When the gas within NGC 1427A collides with the Fornax gas, it is compressed to the point that it starts to collapse under its own gravity. This leads to formation of the myriad of new stars seen across NGC 1427A, which give the galaxy an overall arrowhead shape that appears to point in the direction of the galaxy's high-velocity motion."

Hypervelocity stars
"To date, all of the reported hypervelocity stars (HVSs), which are believed to be ejected from the Galactic center, are blue and therefore almost certainly young.”

Def. a high-velocity star moving through space with an abnormally high velocity relative to the surrounding interstellar medium is called a runaway star.

Clouds
Def. a visible mass of


 * 1) water droplets suspended in the air ...
 * 2) dust,
 * 3) steam ...
 * 4) smoke ...
 * 5) a group or swarm is called a cloud.

Clouds have been observed on other planets and moons within the Solar System, but, due to their different temperature characteristics, they are composed of other substances such as methane, ammonia, and sulfuric acid.

Aerometeors
Def. a discrete unit of air, wind, or mist traveling or falling through or partially through an atmosphere is called an aerometeor.

Def. any of the high-speed, high-altitude air currents that circle the Earth in a westerly direction is called a jet stream.

Plasma meteors
A coronal cloud is a cloud, or cloud-like, natural astronomical entity, composed of plasma and usually associated with a star or other astronomical object where the temperature is such that X-rays are emitted. While small coronal clouds are above the photosphere of many different visual spectral type stars, others occupy parts of the interstellar medium (ISM), extending sometimes millions of kilometers into space, or thousands of light-years, depending on the size of the associated object such as a galaxy.

At left is a radiated object and its associated phenomena.

Ultra-violet studies of Mira by NASA's Galaxy Evolution Explorer (Galex) space telescope have revealed that it sheds a trail of material from the outer envelope, leaving a tail 13 light-years in length, formed over tens of thousands of years. It is thought that a hot bow-wave of compressed plasma/gas is the cause of the tail; the bow-wave is a result of the interaction of the stellar wind from Mira A with gas in interstellar space, through which Mira is moving at an extremely high speed of 130 kilometres/second (291,000 miles per hour). The tail consists of material stripped from the head of the bow-wave, which is also visible in ultra-violet observations. Mira's bow-shock will eventually evolve into a planetary nebula, the form of which will be considerably affected by the motion through the interstellar medium (ISM).

Gaseous meteors
Gaseous objects have at least one chemical element or compound present in the gaseous state. These gaseous components make up at least 50 % of the detectable portion of the gaseous object. Atmospheric astronomy determines whether gaseous objects have layers or spherical portions predominantly composed of gas.

Within these spherical portions may occur various gaseous meteors such as clouds, winds, or streams.

Liquid meteors
Liquid water precipitation falls from the atmosphere and reaches the ground, such as drizzle and rain. Suspended liquid water particles may form and remain suspended in the air (damp haze, cloud, fog, and mist), or may be lifted by the wind from the Earth’s surface (blowing spray) causing restrictions to visibility.

Rocky meteors
"A skydiver may have captured the first film ever of a meteorite plunging down at terminal velocity, also known as its “dark flight” stage."

"The footage was captured in 2012 by a helmet cam worn by Anders Helstrup as he and other members of the Oslo Parachute Club jumped from a small plane that took off from an airport in Hedmark, Norway."

“It can’t be anything else. The shape is typical of meteorites -- a fresh fracture surface on one side, while the other side is rounded.”

“It has never happened before that a meteorite has been filmed during dark flight; this is the first time in world history.”

"Having the rock in hand would certainly help. But despite triangulations and analyses, Helstrup and his recruits still haven’t found it."

Meteoroids
Def. a relatively small (sand- to boulder-sized) fragment of debris in a solar system is called a meteoroid.

"As of 2011 the International Astronomical Union officially defines a meteoroid as a solid object moving in interplanetary space, of a size considerably smaller than an asteroid and considerably larger than an atom".

The visible path of a meteoroid that enters the Earth's atmosphere (or another body's) atmosphere is called a meteor, or colloquially a shooting star or falling star. If a meteoroid reaches the ground and survives impact, then it is called a meteorite.

Beech and Steel, writing in Quarterly Journal of the Royal Astronomical Society, proposed a new definition where a meteoroid is between 100 µm and 10 m across. Following the discovery and naming of asteroids below 10 m in size (e.g., 2008 TC3), Rubin and Grossman refined the Beech and Steel definition of meteoroid to objects between 10 µm and 1 m in diameter. The [near-Earth object] NEO definition includes larger objects, up to 50 m in diameter, in this category. Very small meteoroids are known as micrometeoroids (see also interplanetary dust).

The composition of meteoroids can be determined as they pass through Earth's atmosphere from their trajectories and the light spectra of the resulting meteor. Their effects on radio signals also give information, especially useful for daytime meteors which are otherwise very difficult to observe.

The light spectra, combined with trajectory and light curve measurements, have yielded various compositions and densities, ranging from fragile snowball-like objects with density about a quarter that of ice, to nickel-iron rich dense rocks.

In meteoroid ablation spheres from deep-sea sediments, "[t]he silicate spheres are the most dominant group."

From these trajectory measurements, meteoroids have been found to have many different orbits, some clustering in streams (see Meteor showers) often associated with a parent comet, others apparently sporadic. Debris from meteoroid streams may eventually be scattered into other orbits. ... Meteoroids travel around the Sun in a variety of orbits and at various velocities. The fastest ones move at about 26 miles per second (42 kilometers per second) through space in the vicinity of Earth's orbit. The Earth travels at about 18 miles per second (29 kilometers per second). Thus, when meteoroids meet the Earth's atmosphere head-on (which would only occur if the meteors were in a retrograde orbit), the combined speed may reach about 44 miles per second (71 kilometers per second). Meteoroids moving through the earth's orbital space average about 20 km/s.

Fireballs
A relatively small percentage of meteoroids hit the Earth's atmosphere and then pass out again: these are termed Earth-grazing fireballs (for example The Great Daylight 1972 Fireball).

For 2011 there are 4589 fireball records at the American Meteor Society.

"At 66 kilometers (41 miles) per second, they appear as fast streaks, faster by a hair than their sisters, the Eta Aquarids of May. And like the Eta Aquarids, the brightest of family tend to leave long-lasting trains. Fireballs are possible three days after maximum."

Bolides
Def. a fireball reaching magnitude &minus;14 or brighter is called a bolide.

Def. a fireball reaching an magnitude &minus;17 or brighter is called a superbolide.

Meteor showers
Meteors may occur in showers, which arise when the Earth passes through a trail of debris left by a comet, or as "random" or "sporadic" meteors, not associated with a specific single cause. A number of specific meteors have been observed, largely by members of the public and largely by accident.

Cryometeors
A megacryometeor is a very large chunk of ice sometimes called huge hailstones, but do not need to form in thunderstorms.

Lithometeors
Def. a suspension of dry dust in the atmosphere is called a lithometeor.

Def. the solid material thrown into the air by a volcanic eruption that settles on the surrounding areas is called tephra.

Micrometeors
A micrometeoroid is a tiny meteoroid; a small particle of rock in space, usually weighing less than a gram. A micrometeorite is such a particle that survives passage through the Earth's atmosphere and reaches the Earth's surface.

Micrometeoroids are extremely common in space. [These tiny] particles are a major contributor to space weathering processes. When they hit the surface of the Moon, or any airless body (Mercury, the asteroids, etc.), the resulting melting and vaporization causes darkening and other optical changes in the regolith.

Micrometeoroids have less stable orbits than meteoroids, due to their greater surface area to mass ratio.

Micrometeoroids pose a significant threat to space exploration. Their velocities relative to a spacecraft in orbit average 10 kilometers per second (22,500 mph), and resistance to micrometeoroid impact is a significant design challenge for spacecraft and space suit designers (See Thermal Micrometeoroid Garment). While the tiny sizes of most micrometeoroids limits the damage incurred, the high velocity impacts will constantly degrade the outer casing of spacecraft in a manner analogous to sandblasting. Long term exposure can threaten the functionality of spacecraft systems.

Hydrometeors
Def. precipitation products of the condensation of atmospheric water vapour are called hydrometeors.

Def. any or all of the forms of water particles, whether liquid or solid, that fall from the atmosphere are called precipitation.

Particles
The Comprehensive Suprathermal and Energetic Particle Analyzer (COSTEP) aboard SOHO "detects and classifies very energetic particle populations of solar, interplanetary, and galactic origin."

Ionizing radiation
While large objects may induce the gain or loss of charge from another object, ionizing radiation is usually thought of as on the order of or smaller than an atom.

Different types of ionizing radiation behave in different ways, so different shielding techniques are used.
 * 1) Particle radiation consists of a stream of charged or neutral particles, both charged ions and subatomic elementary particles. This includes solar wind, cosmic radiation, and neutron flux in nuclear reactors.
 * 2) Alpha particles (helium nuclei) are the least penetrating.  Even very energetic alpha particles can be stopped by a single sheet of paper.
 * 3) Beta particles (electrons) are more penetrating, but still can be absorbed by a few millimeters of aluminum. However, in cases where high energy beta particles are emitted  shielding must be accomplished with low density materials, e.g. plastic, wood, water or acrylic glass (Plexiglas, Lucite). This is to reduce generation of Bremsstrahlung X-rays.  In the case of beta+ radiation (positrons), the gamma radiation from the electron-positron annihilation reaction poses additional concern.
 * 4) Neutron radiation is not as readily absorbed as charged particle radiation, which makes this type highly penetrating. Neutrons are absorbed by nuclei of atoms in a nuclear reaction. This most-often creates a secondary radiation hazard, as the absorbing nuclei transmute to the next-heavier isotope, many of which are unstable.
 * 5) Cosmic radiation is not a common concern, as the Earth's atmosphere absorbs it and the magnetosphere acts as a shield, but it poses a problem for satellites and astronauts and frequent fliers are also at a slight risk. Cosmic radiation is extremely high energy, and is very penetrating.
 * 6) Electromagnetic radiation consists of emissions of electromagnetic waves, the properties of which depend on the wavelength.
 * 7) X-ray and gamma radiation are best absorbed by atoms with heavy nuclei; the heavier the nucleus, the better the absorption. In some special applications, depleted uranium is used, but lead is much more common; several centimeters are often required. Barium sulfate is used in some applications too. However, when cost is important, almost any material can be used, but it must be far thicker. Most nuclear reactors use thick concrete shields to create a bioshield with a thin water cooled layer of lead on the inside to protect the porous concrete from the coolant inside. The concrete is also made with heavy aggregates, such as Baryte, to aid in the shielding properties of the concrete.
 * 8) Ultraviolet (UV) radiation is ionizing but it is not penetrating, so it can be shielded by thin opaque layers such as sunscreen, clothing, and protective eyewear. Protection from UV is simpler than for the other forms of radiation above, so it is often considered separately.

In some cases, improper shielding can actually make the situation worse, when the radiation interacts with the shielding material and creates bremsstrahlung secondary radiation that absorbs in the organisms more readily.

Cosmic rays


Cosmic rays are energetic charged subatomic particles, originating in outer space.

At right is an image indicating the range of cosmic-ray energies. The flux for the lowest energies (yellow zone) is mainly attributed to solar cosmic rays, intermediate energies (blue) to galactic cosmic rays, and highest energies (purple) to extragalactic cosmic rays. "Cosmic rays arise from galactic source accelerators."

Cosmic rays may be upwards of a ZeV (1021 eV).

About 89% of cosmic rays are simple protons or hydrogen nuclei, 10% are helium nuclei of alpha particles, and 1% are the nuclei of heavier elements. Solitary electrons constitute much of the remaining 1%.

Def. cosmic rays that originate from astrophysical sources are called primary cosmic rays.

Def. cosmic rays that are created when primary cosmic rays interact with interstellar matter are called secondary cosmic rays.

Def. low energy cosmic rays associated with solar flares are called solar cosmic rays.

Cosmic rays are not charge balanced; that is, positive ions heavily outnumber electrons. The positive ions are
 * 1) free protons,
 * 2) alpha particles (helium nuclei),
 * 3) lithium nuclei,
 * 4) beryllium nuclei, and
 * 5) boron nuclei.

Neutrals
Neutrals are usually neutral atoms, or molecules. But they also can be neutral subatomic particles such as the neutron, neutral pions, and the neutrino.

Subatomics
Subatomics involves one or more subatomic particles or radiation. The bare nuclei of atoms may qualify as a form of subatomics.

Def.
 * 1) particles that are constituents of the atom, or are smaller than an atom; such as proton, neutron, electron, etc or
 * 2) any length or mass that is smaller in scale than a the diameter of a hydrogen atom

are called subatomics, or subatomic, respectively.

As a bare uranium nucleus is smaller than a hydrogen atom in diameter, but much larger in mass, it qualifies as one of the subatomics. Here, subatomic is used to mean smaller than the diameter of a hydrogen atom.

Lithium nuclei
The "evidence for the overwhelming majority of the Li-atoms in photospheres has its origin not only in nuclear synthesis near the stellar centers, but also by active processes in stellar atmospheres. [...] the lithium [resonance] line [is] near 478 keV."

"Approximately 90% of lithium atoms originate from α - α reactions for the typical spectra of an accelerated particles on the Sun [...] During impulsive flares, interaction between the accelerated particles and the ambient medium occurs mainly at low altitudes, i.e., close to the footprints of loops."

Alphas
About 89% of cosmic rays are simple protons or hydrogen nuclei, 10% are helium nuclei or alpha particles, and 1% are the nuclei of heavier elements. Solitary electrons constitute much of the remaining 1%.

Helions
Def. a nucleus of a helium-3 atom" is called a helion.

Tritons
Energetic deuterons and tritons have been detected in solar flares.

Deuterons
"The flux [of deuterons in cosmic rays at a geomagnetic latitude of 7.6°N] is found to be 4 ± 1.3 M-2 sec-1 sterad-1".

Baryons
In "dense nuclear matter, such as neutron stars [it] has recently been discovered that kaon condensation in nuclear matter at a density of a few times normal nuclear matter may significantly reduce the upper mass limit of neutron stars [...] This clearly has an impact on astronomical observations. By exploiting the electron fermi level, we are able to predict kaon production at reasonable baryon number densities [...] Experimental detection of [dibaryons, hyperons] is a subtle matter [...] there is strong theoretical evidence that such states [as the dibaryon] do exist in nature. [...] the lightest dibaryon [...] is energetically stable against strong decay to [ΛΛ baryons] by 88 MeV. [The H dibaryon] is bound by 250 MeV."

Radioactivity
Def. a spontaneous emission of an α ray, β ray, or γ ray by the disintegration of an atomic nucleus is called radioactivity.

Although alpha, beta, and gamma radiations were found most commonly, other types of decay were eventually discovered. Shortly after the discovery of the positron in cosmic ray products, it was realized that the same process that operates in classical beta decay can also produce positrons (positron emission). In an analogous process, instead of emitting positrons and neutrinos, some proton-rich nuclides were found to capture their own atomic electrons (electron capture), and emit only a neutrino (and usually also a gamma ray). Each of these types of decay involves the capture or emission of nuclear electrons or positrons, and acts to move a nucleus toward the ratio of neutrons to protons that has the least energy for a given total number of nucleons (neutrons plus protons).

Hadrons
Hadrons are subatomic particles of a type including baryons and mesons that can take part in the strong interaction and may be useful in astronomy.

A hadron, like an atomic nucleus, is a composite particle held together by the strong force Hadrons are categorized into two families: baryons (such as protons and neutrons) and mesons.

Radioactivity emissions
The nuclei of some atoms spontaneously disintegrate from one form of isotope to another until they reach a stable form. These atoms emit particles (alpha or beta) or electromagnetics (X-ray or gamma) which are different in charge, size, penetrating power and ionization energy.

In decay, or "positron emission", the weak interaction converts a nucleus into its next-lower neighbor on the periodic table while emitting an positron  and an electron neutrino :



^A_ZN \rightarrow ~ ^{A}_{Z-1}N' + e^+ + \nu_e. $$

decay cannot occur in an isolated proton because it requires energy due to the mass of the neutron being greater than the mass of the proton. decay can only happen inside nuclei when the value of the binding energy of the mother nucleus is less than that of the daughter nucleus. The difference between these energies goes into the reaction of converting a proton into a neutron, a positron and a neutrino and into the kinetic energy of these particles.

Positron emission or beta plus decay' (β+ decay) is a type of beta decay in which a proton is converted, via the weak force, to a neutron, releasing a positron and a neutrino.

Isotopes which undergo this decay and thereby emit positrons include carbon-11, potassium-40, nitrogen-13, oxygen-15, fluorine-18, and iodine-121. As an example, the following equation describes the beta plus decay of carbon-11 to boron-11, emitting a positron and a neutrino:



^{11}_{6}C \rightarrow ~ ^{11}_{5}B + e^+ + \nu_e + \gamma {(0.96 MeV)}. $$

Antimatter
Def. a subatomic particle corresponding to another particle with the same mass, spin and mean lifetime but with charge, parity, strangeness and other quantum numbers flipped in sign is called an antiparticle.

Def. matter that is composed of antiparticles of those that constitute normal matter is called antimatter.

Annihilations
The positron or antielectron is the antiparticle or the antimatter counterpart of the electron. The positron has an electric charge of +1e, a spin of ½, and has the same mass as an electron. When a low-energy positron collides with a low-energy electron, annihilation occurs, resulting in the production of two or more gamma ray photons.

Def. the process of a particle and its corresponding antiparticle combining to produce energy is called annihilation.

The figure at right shows a positron (e+) emitted from an atomic nucleus together with a neutrino (v). Subsequently, the positron moves randomly through the surrounding matter where it hits several different electrons (e-) until it finally loses enough energy that it interacts with a single electron. This process is called an "annihilation" and results in two diametrically emitted photons with a typical energy of 511 keV each. Under normal circumstances the photons are not emitted exactly diametrically (180 degrees). This is due to the remaining energy of the positron having conservation of momentum.

Electron–positron annihilation occurs when an electron and a positron (, the electron's antiparticle) collide. The result of the collision is the annihilation of the electron and positron, and the creation of gamma ray photons or, at higher energies, other particles:


 * + &rarr;  +

The process [does] satisfy a number of conservation laws, including:


 * Conservation of electric charge. The net charge before and after is zero.
 * Conservation of linear momentum and total energy. This forbids the creation of a single gamma ray. However, in quantum field theory this process is described; see examples of annihilation.
 * Conservation of angular momentum.

As with any two charged objects, electrons and positrons may also interact with each other without annihilating, in general by elastic scattering.

The creation of only one photon can occur for tightly bound atomic electrons. In the most common case, two photons are created, each with energy equal to the rest energy of the electron or positron (511 keV). It is also common for three to be created, since in some angular momentum states, this is necessary to conserve C parity. Any larger number of photons can be created, but the probability becomes lower with each additional photon. When either the electron or positron, or both, have appreciable kinetic energies, other heavier particles can also be produced (such as D mesons), since there is enough kinetic energy in the relative velocities to provide the rest energies of those particles. Photons and other light particles [may be produced], but they will emerge with higher energies.

At energies near and beyond the mass of the carriers of the weak force, the W and Z bosons, the strength of the weak force becomes comparable with electromagnetism. It becomes much easier to produce particles such as neutrinos that interact only weakly.

The heaviest particle pairs yet produced by electron–positron annihilation are – pairs. The heaviest single particle is the Z boson.

Annihilation radiation is not monoenergetic, unlike gamma rays produced by radioactive decay. The production mechanism of annihilation radiation introduces Doppler broadening. The annihilation peak produced in a gamma spectrum by annihilation radiation therefore has a higher full width at half maximum (FWHM) than other gamma rays in [the] spectrum. The difference is more apparent with high resolution detectors, such as Germanium detectors, than with low resolution detectors such as Sodium iodide Because of their well-defined energy (511 keV) and characteristic, Doppler-broadened shape, annihilation radiation can often be useful in defining the energy calibration of a gamma ray spectrum.

Positroniums
Def. an exotic atom consisting of a positron and an electron, but having no nucleus or an onium consisting of a positron (anti-electron) and an electron, as a particle–anti-particle bound pair is called positronium.

Being unstable, the two particles annihilate each other to produce two gamma ray photons after an average lifetime of 125 ps or three gamma ray photons after 142 ns in vacuum, depending on the relative spin states of the positron and electron.

The singlet state with antiparallel spins ([spin quantum number] S = 0, Ms = 0) is known as para-positronium (p-Ps) and denoted. It has a mean lifetime of 125 picoseconds and decays preferentially into two gamma quanta with energy of 511 keV each (in the center of mass frame). Detection of these photons allows for the reconstruction of the vertex of the decay ... Para-positronium can decay into any even number of photons (2, 4, 6, ...), but the probability quickly decreases as the number increases: the branching ratio for decay into 4 photons is $1.439$.

para-positronium lifetime (S = 0):
 * $$t_{0} = \frac{2 \hbar}{m_e c^2 \alpha^5} = 1.244 \times 10^{-10} \; \text{s}$$

The triplet state with parallel spins (S = 1, Ms = −1, 0, 1) is known as ortho-positronium (o-Ps) and denoted 3S1. The triplet state in vacuum has a mean lifetime of $142.05 ns$ and the leading mode of decay is three gamma quanta. Other modes of decay are negligible; for instance, the five photons mode has branching ratio of ~$1$.

ortho-positronium lifetime (S = 1):
 * $$t_{1} = \frac{\frac{1}{2} 9 h}{2 m_e c^2 \alpha^6 (\pi^2 - 9)} = 1.386 \times 10^{-7} \; \text{s}$$

Pair production
The reverse reaction, electron–positron creation, is a form of pair production governed by two-photon physics.

Two-photon physics, also called gamma-gamma physics, [studies] the interactions between two photons. If the energy in the center of mass system of the two photons is large enough, matter can be created.


 * &rarr; +

In nuclear physics, [the above reaction] occurs when a high-energy photon interacts with a nucleus. The photon must have enough energy [> 2*511 keV, or 1.022 MeV] to create an electron plus a positron. Without a nucleus to absorb momentum, a photon decaying into electron-positron pair (or other pairs for that matter [such as a muon and anti-muon or a tau and anti-tau] can never conserve energy and momentum simultaneously.

These interactions were first observed in Patrick Blackett's counter-controlled cloud chamber. In 2008 the Titan laser aimed at a 1-millimeter-thick gold target was used to generate positron–electron pairs in large numbers. . "The LLNL scientists created the positrons by shooting the lab's high-powered Titan laser onto a one-millimeter-thick piece of gold."

Neutrons
"Due to the very low energy of the colliding protons in the Sun, only states with no angular momentum (s-waves) contribute significantly. One can consider it as a head-on collision, so that angular momentum plays no role. Consequently, the total angular momentum is the sum of the spins, and the spins alone control the reaction. Because of Pauli's exclusion principle, the incoming protons must have opposite spins. On the other hand, in the only bound state of deuterium, the spins of the neutron and proton are aligned. Hence a spin flip must take place [...] The strength of the nuclear force which holds the neutron and the proton together depends on the spin of the particles. The force between an aligned proton and neutron is sufficient to give a bound state, but the interaction between two protons does not yield a bound state under any circumstances. Deuterium has only one bound state."

The "force acting between the protons and the neutrons [is] the strong force".

"A potential of 36 MeV is needed to get just one energy state."

The width of a bound proton and neutron is "2.02 x 10-13 cm".

Protons
The proton is a subatomic particle with the symbol or  and a positive electric charge of 1 elementary charge. One or more protons are present in the nucleus of each atom, along with neutrons. The number of protons in each atom is its atomic number.

Nucleon spin structure describes the partonic structure of proton intrinsic angular momentum (spin). The key question is how the nucleon's spin, whose magnitude is 1/2ħ, is carried by its [suggested] constituent partons (quarks and gluons). In the late 1980s, the European Muon Collaboration (EMC) conducted experiments that suggested the spin carried by quarks is not sufficient to account for the total spin of [protons]. This finding astonished particle physicists at that time, and the problem of where the missing spin lies is sometimes referred to as the "proton spin crisis".

Experimental research on these topics has been continued by the Spin Muon Collaboration (SMC) and the COMPASS experiment at CERN, experiments E154 and E155 at [SLAC National Accelerator Laboratory] SLAC, HERMES at DESY, experiments at [Thomas Jefferson National Accelerator Facility] JLab and RHIC, and others. Global analysis of data from all major experiments confirmed the original EMC discovery and showed that the quark spin [may] contribute about 30% to the total spin of the nucleon.

New measurements performed by European scientists reveal that the radius of the proton is 4 percent smaller than previously estimated.

The antiproton (, pronounced p-baer) is the antiparticle of the proton. Antiprotons are stable, but they are typically short-lived since any collision with a proton will cause both particles to be annihilated in a burst of energy.

Antiprotons have been detected in cosmic rays for over 25 years, first by balloon-borne experiments and more recently by satellite-based detectors. The standard picture for their presence in cosmic rays is that they are produced in collisions of cosmic ray protons with nuclei in the interstellar medium, via the reaction, where A represents a nucleus:


 * + A →  +  +  + A

The secondary antiprotons then propagate through the galaxy, confined by the galactic magnetic fields. Their energy spectrum is modified by collisions with other atoms in the interstellar medium. The antiproton cosmic ray energy spectrum is now measured reliably and is consistent with this standard picture of antiproton production by cosmic ray collisions.

Mesons
Mesons are hadronic subatomic particles, bound together by the strong interaction. Because mesons are composed of sub-particles, they have a physical size, with a radius roughly one femtometre, which is about $2/3$ the size of a proton or neutron.

Charged mesons decay (sometimes through intermediate particles) to form electrons and neutrinos. Uncharged mesons may decay to photons.

Mesons are not produced by radioactive decay, but appear in nature only as short-lived products of very high-energy interactions in matter In cosmic ray interactions, for example, such particles are ordinary protons and neutrons. Mesons are also frequently produced artificially in high-energy particle accelerators that collide protons, anti-protons, or other particles.

Mesons are subject to "both the weak and strong interactions. Mesons with net electric charge also participate in the electromagnetic interaction.

While no meson is stable, those of lower mass are nonetheless more stable than the most massive mesons, and are easier to observe and study in particle accelerators or in cosmic ray experiments. They are also typically less massive than baryons, meaning that they are more easily produced in experiments, and thus exhibit certain higher energy phenomena more readily than baryons composed of the same quarks would.

Potential mesons to be detected astronomically include: π, ρ, η, η′, φ, ω, J/ψ, ϒ, θ, K, B, D, and T.

Single π0 production occurs "in neutral current neutrino interactions with water by a 1.3 GeV wide band neutrino beam."

"The Gamma-Ray Spectrometer (GRS) on [Solar Maximum Mission] SMM has detected [...] at least two of the flares have spectral properties >40 MeV that require gamma rays from the decay of neutral pions. [Pion] production can occur early in the impulsive phase as defined by hard X-rays near 100 keV."

Gamma-ray "emission matches remarkably well both the position and shape of the inner [supernova remnant] SNR shocked plasma. Furthermore, the gamma-ray spectrum shows a prominent peak near 1 GeV with a clear decrement at energies below a few hundreds of MeV as expected from neutral pion decay."

Beta-particles
Beta particles are high-energy, high-speed electrons or positrons emitted by certain types of radioactive nuclei such as potassium-40. The beta particles emitted are a form of ionizing radiation also known as beta rays. The production of beta particles is termed beta decay. They are designated by the Greek letter beta (β).

Electrons
The electron is a subatomic particle with a negative charge, equal to -1.60217646x10-19 C. Current, or the rate of flow of charge, is defined such that one coulomb, so 1/-1.60217646x10-19, or 6.24150974x1018 electrons flowing past a point per second give a current of one ampere. The charge on an electron is often given as -e. note that charge is always considered positive, so the charge of an electron is always negative.

The electron has a mass of 9.10938188x10-31 kg, or about 1/1840 that of a proton. The mass of an electron is often written as me.

When working, these values can usually be safely approximated to:


 * -e = -1.60x10-19 C
 * me = 9.11x10-31kg

It has no known components or substructure; in other words, it is generally thought to be an elementary particle. The intrinsic angular momentum (spin) of the electron is a half-integer value in units of ħ, which means that it is a fermion.

Def. a quasiparticle produced as a result of electron spin-charge separation is called a chargon.

A chargon possesses the charge of an electron without a spin.

A spinon, in turn, possesses the spin of an electron without charge. The suggestion is that an elementary particle such as a positron may consist of at least two parts: spin and charge.

An electron may be a negative chargon plus a spinon.

Positrons
"The two conversions of protons into neutrons are assumed to take place inside the nucleus, and the extra positive charge is emitted as a positron."

Def. the antimatter equivalent of an electron, having the same mass but a positive charge is called a positron.

Tauons
"For ultrahigh energies the neutrino spectrum at the detector is influenced by neutrino-nucleon interactions and tauon decays during the passage through the interior of the earth."

Def. A lepton is a spin 1/2 particle a fermion that does not interact via the strong force. To date there are three known types of leptons. They are the electron, the muon ($$\mu$$), and the tauon ($$\tau$$) with their corresponding anti-particles that carry opposite charge ($$+$$ instead of $$-$$).

Muons
"TeV muons from γ ray primaries ... are rare because they are only produced by higher energy γ rays whose flux is suppressed by the decreasing flux at the source and by absorption on interstellar light."

The muon from the Greek letter mu (μ) used to represent it) is an elementary particle similar to the electron, with unitary negative electric charge (−1) and a spin of $1/2$. Together with the electron, the tau, and the three neutrinos, it is classified as a lepton. As is the case with other leptons, the muon is not believed to have any sub-structure at all (i.e., is not thought to be composed of any simpler particles).

The muon is an unstable subatomic particle with a mean lifetime of $2.2 us$. This comparatively long decay lifetime (the second longest known) is due to being mediated by the weak interaction. The only longer lifetime for an unstable subatomic particle is that for the free neutron, a baryon particle composed of quarks, which also decays via the weak force. Muon decay produces three particles, an electron plus two neutrinos of different types.

Like all elementary particles, the muon has a corresponding antiparticle of opposite charge (+1) but equal mass and spin: the antimuon (also called a positive muon). Muons are denoted by and antimuons by.

Neutrinos
A neutrino is an electrically neutral, weakly interacting elementary subatomic particle with half-integer spin. ... Neutrinos do not carry electric charge, which means that they are not affected by the electromagnetic forces that act on charged particles such as electrons and protons. Neutrinos are affected only by the weak sub-atomic force, of much shorter range than electromagnetism, and gravity, which is relatively weak on the subatomic scale. They are therefore able to travel great distances through matter without being affected by it.

"If neutrinos have negligible rest mass, the present density expected for relic neutrinos from the big bang is nν = 110 (Tγ/2.7 K)3 cm–3 for each two-component species. This is of order the photon density nγ, differing just by a factor 3/11 (i.e. a factor 3/4 because neutrinos are fermions rather than bosons, multiplied by 4/11, the factor by which the neutrinos are diluted when e+–e– annihilation boosts the photon density). This conclusion holds for non-zero masses, provided that mvc2 is far below the thermal energy (~ 5 MeV) at which neutrinos decoupled from other species and that the neutrinos are stable for the Hubble time. Comparison with the baryon density, related to Ω via nb = 1.5 x 10–5 Ωb h2 cm–3, shows that neutrinos outnumber baryons by such a big factor that they can be dynamically dominant over baryons even if their masses are only a few electron volts. In fact, a single species of neutrino would yield a contribution to Ω of Ωv = 0.01 h–2 (mv)eV, so if h = 0.5, only 25 eV is sufficient to provide the critical density."

"Neutrinos of nonzero mass would be dynamically important not only for the expanding universe as a whole but also for large bound systems such as clusters of galaxies. This is because they would now be moving slowly: if the universe had cooled homogeneously, primordial neutrinos would now be moving at around 200 (mv)-1eV km s–1. They would be influenced even by the weak (~ 10–5 c2) gravitational potential fluctuations of galaxies and clusters. If the three (or more) types of neutrinos have different masses, then the heaviest will obviously be gravitationally dominant, since the numbers of each species should be the same."

Electromagnetics
Electromagnetics is most familiar as light, or electromagnetic radiation.

Superluminals
"The existence of superluminal energy transfer has not been established so far, and one may ask why. There is the possibility that superluminal quanta just do not exist, the vacuum speed of light being the definitive upper bound. There is another explanation, the interaction of superluminal radiation with matter is very small, the quotient of tachyonic and electric fine-structure constants being q2/e2 ≈ 1.4 x 10-11 [5], and therefore superluminal quanta are hard to detect."

Cherenkovs
At right is an example of Cherenkov radiation. Cherenkov radiation (also spelled Čerenkov) is electromagnetic radiation emitted when a charged particle (such as an electron) passes through a dielectric medium at a speed greater than the phase velocity of light in that medium. Cherenkov radiation is an example of medium specific superluminals.

Entities
The electron is a subatomic particle with a negative charge, equal to -1.60217646x10-19 C. Current, or the rate of flow of charge, is defined such that one coulomb, so 1/-1.60217646x10-19, or 6.24150974x1018 electrons flowing past a point per second give a current of one ampere. The charge on an electron is often given as -e. note that charge is always considered positive, so the charge of an electron is always negative.

Objects
Electrons "provide remote-sensing observations of distant targets in the heliosphere - the Sun, the Moon, Jupiter, and various heliospheric structures."

The image at right is a painting by artist Giorgio Vasari (1511–1574). The main focus is on Cronus (Saturn) castrating Uranus (the Greek sky god). As both Uranus and Cronus are represented by men, this suggests that they were similar in nature. "[T]he ancients’ religions and mythology speak for their knowledge of Uranus; the dynasty of gods had Uranus followed by Saturn, and the latter by Jupiter. ... It is quite possible that the planet Uranus is the very planet known by this name to the ancients. The age of Uranus preceded the age of Saturn; it came to an end with the “removal” of Uranus by Saturn. Saturn is said to have emasculated his father Uranus."

Continua
Def. a continuous series or whole, no part of which is noticeably different from its adjacent parts, although the ends or extremes of it are very different from each other is called a continuum.

Above is the electromagnetic spectrum. When each wavelength has the same intensity and background, the entire spectrum is a continuum. More generally, the electromagnetic spectrum, is often termed as either continuous (with energy at all wavelengths) or discrete (energy at only certain wavelengths).

Emissions
Def. the act of sending or throwing out; the act of sending forth or putting into circulation is called emission.

In Draft:physics, emission is the process by which a higher energy quantum mechanical state of a particle becomes converted to a lower one through the emission of a photon, resulting in the production of light. The frequency of light emitted is a function of the energy of the transition. Since energy must be conserved, the energy difference between the two states equals the energy carried off by the photon. The energy states of the transitions can lead to emissions over a very large range of frequencies. For example, visible light is emitted by the coupling of electronic states in atoms and molecules (then the phenomenon is called fluorescence or phosphorescence). On the other hand, nuclear shell transitions can emit high energy gamma rays, while nuclear spin transitions emit low energy radio waves.

Absorptions
Def. the act or process of including so that a separate existence is no longer is called absorption.

"There are a number of ways to quantify how quickly and effectively radiation is absorbed.

The attenuation coefficient is a quantity that characterizes how easily a material or medium can be penetrated by a beam of light, sound, particles, or other energy or matter.

The range of a heavy charged particle is approximately proportional to the mass of the particle and the inverse of the density of the medium, and is a function of the initial velocity of the particle.

Def. the average energy loss of the particle per unit path length is called stopping power.

Bands
Spectral bands are part of optical spectra of polyatomic systems, including condensed materials, large molecules, etc. Each line corresponds to one level in the atom splits in the molecules. When the number of atoms is large, one gets a continuum of energy levels, the so called "spectral bands". They are often labeled in the same way as the monatomic lines.

Band spectra is the name given to a group of lines that are closely spaced and arranged in a regular sequence that appears to be a band. It is a colored band, separated by dark spaces on the two sides and arranged in a regular sequence. In one band, there are various sharp and wider color lines, that are closer on one side and wider on other. The intensity in each band falls off from definite limits and indistinct on the other side. In complete band spectra, there is a number lines in a band.

The band spectrum is the combination of many different spectral lines, resulting from rotational, vibrational and electronic transition.

Backgrounds
Background radiation is the ubiquitous ionizing radiation that the general population is exposed to, including natural and artificial sources. Both natural and artificial background radiation varies by location.

The worldwide average natural dose to humans is about 2.4 millisievert (mSv) per year.

The biggest source of natural background radiation is airborne radon, a radioactive gas that emanates from the ground. Radon and its isotopes, parent radionuclides, and decay products all contribute to an average inhaled dose of 1.26 mSv/a. Radon is unevenly distributed and variable with weather, such that much higher doses apply to many areas of the world, where it represents a significant health hazard. Concentrations over 500 times higher than the world average have been found inside buildings in Scandinavia, the United States, Iran, and the Czech Republic.

Terrestrial radiation usually only includes sources that remain external to the body. The major radionuclides of concern are potassium, uranium and thorium and their decay products, some of which, like radium and radon are intensely radioactive but occur in low concentrations.

An average human contains about 30 milligrams of potassium-40 (40K) and about 10 nanograms (10−8 g) of carbon-14 (14C), which has a decay half-life of 5,730 years. Excluding internal contamination by external radioactive material, the largest component of internal radiation exposure from biologically functional components of the human body is from potassium-40. The decay of about 4,000 nuclei of 40K per second makes potassium the largest source of radiation in terms of number of decaying atoms. The energy of beta particles produced by 40K is also about 10 times more powerful than the beta particles from 14C decay. 14C is present in the human body at a level of 3700 Bq with a biological half-life of 40 days. There are about 1,200 beta particles per second produced by the decay of 14C. However, a 14C atom is in the genetic information of about half the cells, while potassium is not a component of DNA. The decay of a 14C atom inside DNA in one person happens about 50 times per second, changing a carbon atom to one of nitrogen. The global average internal dose from radionuclides other than radon and its decay products is 0.29 mSv/a, of which 0.17 mSv/a comes from 40K, 0.12 mSv/a comes from the uranium and thorium series, and 12 μSv/a comes from 14C.

Background radiation may simply be any radiation that is pervasive, whether ionizing or not. A particular example of this is the cosmic microwave background radiation, a nearly uniform glow that fills the sky in the microwave part of the spectrum; stars, galaxies and other objects of interest in radio astronomy stand out against this background.

In a laboratory, background radiation refers to the measured value from any sources that affect an instrument when a radiation source sample is not being measured. This background rate, which must be established as a stable value by multiple measurements, usually before and after sample measurement, is subtracted from the rate measured when the sample is being measured.

Damages
Def. susceptibility of a material to physical or chemical changes induced by radiation is called radiation sensitivity.

The radiation effect depends on the type of the irradiating particles, their energy and the number of incident particles per unit volume.

Def. harmful changes in the properties of materials caused by interactions with ionizing radiation is called radiation damage.

Radiation damage is a term [usually] associated with ionizing radiation.

Radiation may affect materials and devices in deleterious ways:
 * 1) By causing the materials to become radioactive (mainly by neutron activation, or in [the] presence of high-energy gamma radiation by photodisintegration).
 * 2) By nuclear transmutation of the elements within the material including, for example, the production of Hydrogen and Helium which can in turn alter the mechanical properties of the materials and cause swelling and embrittlement.
 * 3) By radiolysis (breaking chemical bonds) within the material, which can weaken it, cause it to swell, polymerize, promote corrosion, cause belittlements, promote cracking or otherwise change its desirable mechanical, optical, or electronic properties.
 * 4) By formation of reactive compounds, affecting other materials (e.g. ozone cracking by ozone formed by ionization of air).
 * 5) By ionization, causing electrical breakdown, particularly in semiconductors employed in electronic equipment, with subsequent currents introducing operation errors or even permanently damaging the devices.

Exposure to radiation causes chemical changes in gases.

High-intensity ionizing radiation in air can produce a visible ionized air glow of telltale bluish-purplish color.

Like gases, liquids lack fixed internal structure; the effects of radiation is therefore mainly limited to radiolysis, altering the chemical composition of the liquids. As with gases, one of the primary mechanisms is formation of free radicals.

All liquids are subject to radiation damage, with few exotic exceptions; e.g. molten sodium, where there are no chemical bonds to be disrupted, and liquid hydrogen fluoride, which produces gaseous hydrogen and fluorine, which spontaneously react back to hydrogen fluoride.

Radiation astronomy
When any effort to acquire a system of laws or knowledge focusing on an astr, aster, or astro, that is, any natural body in the sky especially at night, succeeds in discovering or exploring radiation even in its smallest measurement, radiation astronomy is the name of the effort and the result. Once an entity, source, or object has been detected as having radiation, it may be necessary to determine what the mechanism is. Usually this information provides understanding of the same entity, source, or object. The formation of radiation on Earth and its initial detection by hominins may be associated primarily with the available senses.

Sun
"Energetic photons, ions and electrons from the solar wind, together with galactic and extragalactic cosmic rays, constantly bombard surfaces of planets, planetary satellites, dust particles, comets and asteroids."

Coronal clouds
"Coronal clouds, type IIIg, form in space above a spot area and rain streamers upon it."

A variety of subatomic particle and γ-ray reactions have been observed during solar flares indicating fusion reactions occurring at or above the photosphere. "There are typically 375 gamma-ray flares per solar cycle ... each releasing on average about 1031 erg of kinetic energy in accelerated ions of energy ≥ 1 MeV per nucleon [27]."

"The solar-flare gamma-ray line emission testifies that fresh nuclei are synthesized in abundance in energetic solar events."

"[T]he gamma-ray lines at 478 and 429 keV [are] emitted in the reactions 4He(α,p)7Li and 4He(α,n)7Be, respectively".

Mercury
The mosaic image of the rocky-object Mercury at right shows what appears to be meteor damage over a large portion of the surface.

"The mosaic consists of 18 images taken at 42 s intervals during a 13 minute period when the spacecraft was 200,000 km (about 6 hours prior to closest approach) from the planet."

Mercury's surface is heavily cratered and similar in appearance to Earth's Moon Craters on Mercury range in diameter from small bowl-shaped cavities to multi-ringed impact basins hundreds of kilometers across. They appear in all states of degradation, from relatively fresh rayed craters to highly degraded crater remnants. Mercurian craters differ subtly from lunar craters in that the area blanketed by their ejecta is much smaller, a consequence of Mercury's stronger surface gravity.

Venus
In 1967, Venera-4 found the Venusian magnetic field is much weaker than that of Earth. This magnetic field is induced by an interaction between the ionosphere and the solar wind, Venus's small induced magnetosphere provides negligible protection to the atmosphere against cosmic radiation. This radiation may result in cloud-to-cloud lightning discharges.

Strong 300 km/h winds at the cloud tops circle the planet about every four to five earth days. Venusian winds move at up to 60 times the speed of the planet's rotation, while Earth's fastest winds are only 10% to 20% rotation speed.

While there is little or no water on Venus, there is a phenomenon which is quite similar to snow. The Magellan probe imaged a highly reflective substance at the tops of Venus's highest mountain peaks which bore a strong resemblance to terrestrial snow. This substance arguably formed from a similar process to snow, albeit at a far higher temperature. Too volatile to condense on the surface, it rose in gas form to cooler higher elevations, where it then fell as precipitation. The identity of this substance is not known with certainty, but speculation has ranged from elemental tellurium to lead sulfide (galena).

Earth
In the image at left is an aerial view of the Barringer Meteor Crater about 69 km east of Flagstaff, Arizona USA. Although similar to the aerial view of the Soudan crater, the Barringer Meteor Crater appears angular at the farthest ends rather than round.

Meteor Crater is a meteorite impact crater approximately 43 miles (69 km) east of Flagstaff, near Winslow in the northern Arizona desert of the United States. Because the US Department of the Interior Division of Names commonly recognizes names of natural features derived from the nearest post office, the feature acquired the name of "Meteor Crater" from the nearby post office named Meteor. The site was formerly known as the Canyon Diablo Crater, and fragments of the meteorite are officially called the Canyon Diablo Meteorite. Scientists refer to the crater as Barringer Crater in honor of Daniel Barringer, who was first to suggest that it was produced by meteorite impact.

From space the crater appears almost like a square. The image at right has a resolution of 2 meters per pixel, and illumination is from the right. Layers of exposed limestone and sandstone are visible just beneath the crater rim, as are large stone blocks excavated by the impact.

The Holsinger meteorite is the largest discovered fragment of the meteorite that created Meteor Crater and it is exhibited in the crater visitor center. "The Canyon Diablo meteorite comprises many fragments of the asteroid that impacted at Barringer Crater (Meteor Crater), Arizona, USA. Meteorites have been found around the crater rim, and are named for nearby Canyon Diablo, which lies about three to four miles west of the crater. There are fragments in the collections of museums around the world including the Field Museum of Natural History in Chicago. The biggest fragment ever found is the Holsinger Meteorite, weighing 639 kg, now on display in the Meteor Crater Visitor Center on the rim of the crater.

Moon
Meteorites have been found on the Moon

Lunar origin [of lunar meteors] is established by comparing the mineralogy, the chemical composition, and the isotopic composition between meteorites and samples from the Moon collected by Apollo missions.

Cosmic ray exposure history established with noble gas measurements have shown that all lunar meteorites were ejected from the Moon in the past 20 million years. Most left the Moon in the past 100,000 years.

In the image at left, twenty degrees of latitude of the Moon's disk is completely covered in the overlapping circles of craters. The illumination angles are from all directions, keeping almost all the crater floors in sunlight, but a set of merged crater floors right at the south pole are completely shadowed.

Mars
Martian meteors are thought to be from Mars because they have elemental and isotopic compositions that are similar to rocks and atmosphere gases analyzed by spacecraft on Mars.

The image at right is of the Mackinac Island meteorite, discovered on Mars by the NASA Opportunity rover on October 13, 2009.

At top left is the first meteorite of any type ever identified on another planet. The pitted, basketball-size object is mostly made of iron and nickel. Readings from spectrometers on the rover determined that composition. Opportunity used its panoramic camera to take the images used in this approximately true-color composite on the rover's 339th martian day, or sol (Jan. 6, 2005). This composite combines images taken through the panoramic camera's 600-nanometer (red), 530-nanometer (green), and 480-nanometer (blue) filters.

Comparison of the two meteorites shown here suggests that the left one is a much more recent fall.

Asteroids
Notation let the symbol EC denote Earth-crossing asteroids.

Notation: let the symbol MB denote the main belt of asteroids.

"From the dominant group, the asteroids evolve to intersect the Earth's orbit on a median time scale of about 60 Myr."

"The MB group is the most numerous group of MCs. ... 50 % of the MB Mars-crossers [MCs] become ECs within 59.9 Myr and [this] contribution ... dominates the production of ECs".

Vesta
In the full image of Vesta at right, the rocky-object appears to have suffered from meteor damage.

Vesta, minor-planet designation 4 Vesta, is one of the largest asteroids in the Solar System. It lost some 1% of its mass less than a billion years ago in a collision that left an enormous crater occupying much of its southern hemisphere. Debris from this event has fallen to Earth as howardite–eucrite–diogenite (HED) meteorites, a rich source of information about the asteroid.

Saturn
"[E]rosion from particles making up the icy rings of Saturn are forming rain water that falls on certain parts of the planet. ... tiny ice particles that compose the planet's distinctive rings are sometimes eroded away and then deposited in the planet's upper atmosphere. The droplets then create a kind of rain on the planet. ... charged water molecules rain down only on certain parts of the planet, which show up darker in infrared images. ... The magnetic connection creates a pathway for small ice particles in the rings to slough off into the planet's atmosphere, causing the "ring rain.""

"The most surprising element to us was that these dark regions on the planet are found to be linked — via magnetic field lines — to the solid portions of water-ice within Saturn's ring-plane".

"Saturn is the first planet to show significant interaction between its atmosphere and ring system ... The main effect of ring rain is that it acts to 'quench' the ionosphere of Saturn. In other words, this rain severely reduces the electron densities in regions in which it falls."

"It turns out that a major driver of Saturn's ionospheric environment and climate across vast reaches of the planet are ring particles located some 36,000 miles [60,000 kilometers] overhead ... The ring particles affect both what species of particles are in this part of the atmosphere and where it is warm or cool."

"Where Jupiter is glowing evenly across its equatorial regions, Saturn has dark bands where the water is falling in, darkening the ionosphere".

Titan
"As spring continues to unfold at Saturn, April showers on the planet's largest moon, Titan, have brought methane rain to its equatorial deserts ... Extensive rain from large cloud systems ... has apparently darkened the surface of the moon."

“It's amazing to be watching such familiar activity as rainstorms and seasonal changes in weather patterns on a distant, icy satellite".

"The Saturn system experienced equinox, when the sun lies directly over a planet's equator and seasons change, in August 2009. (A full Saturn “year” is almost 30 Earth years.)"

"Clouds on Titan are formed of methane as part of an Earth-like cycle that uses methane instead of water. On Titan, methane fills lakes on the surface, saturates clouds in the atmosphere, and falls as rain. Though there is evidence that liquids have flowed on the surface at Titan's equator in the past, liquid hydrocarbons, such as methane and ethane, had only been observed on the surface in lakes at polar latitudes. The vast expanses of dunes that dominate Titan's equatorial regions require a predominantly arid climate."

"An arrow-shaped storm appeared in the equatorial regions on Sept. 27, 2010 -- the equivalent of early April in Titan's “year” -- and a broad band of clouds appeared the next month. ... A 193,000-square-mile (500,000-square-kilometer) region along the southern boundary of Titan’s Belet dune field, as well as smaller areas nearby, had become darker. ... this change in brightness is most likely the result of surface wetting by methane rain."

“These outbreaks may be the Titan equivalent of what creates Earth's tropical rainforest climates, even though the delayed reaction to the change of seasons and the apparently sudden shift is more reminiscent of Earth's behavior over the tropical oceans than over tropical land areas”.

At right is an image that shows clouds over the equatorial region of Titan.

"Methane clouds in the troposphere, the lowest part of the atmosphere, appear white here and are mostly near Titan's equator. The darkest areas are surface features that have a low albedo, meaning they do not reflect much light. Cassini observations of clouds like these provide evidence of a seasonal shift of Titan's weather systems to low latitudes following the August 2009 equinox in the Saturnian system. (During equinox, the sun lies directly over the equator. See PIA11667 to learn how the sun's illumination of the Saturnian system changed during the equinox transition to spring in the northern hemispheres and to fall in the southern hemispheres of the planet and its moons.)"

"In 2004, during Titan's late southern summer, extensive cloud systems were common in Titan's south polar region (see PIA06110, PIA06124 and PIA06241). Since 2005, southern polar systems have been observed infrequently, and one year after the equinox, extensive near-equatorial clouds have been seen. This image was taken on Oct. 18, 2010, a little more than one Earth year after the Saturnian equinox, which happens once in roughly 15 Earth years."

"The cloud patterns observed from late southern summer to early southern fall on Titan suggest that Titan's global atmospheric circulation is influenced by both the atmosphere and the surface. The temperature of the surface responds more rapidly to changes in illumination than does the thick atmosphere. Outbreaks such as the clouds seen here may be the Titan equivalent of what creates the Earth's tropical rainforest climates, even though the delayed reaction to the change of seasons and the apparently sudden shift is more reminiscent of the behavior over Earth's tropical oceans than over tropical land areas."

"A few clouds can be seen in Titan's southern latitudes here. See PIA12813 for a movie of clouds moving through the middle southern latitudes of Titan. Some clouds are also visible in the high northern latitudes here. See PIA12811 and PIA12812 for movies showing clouds near the moon's north pole. This view looks toward the Saturn-facing side of Titan (5,150 kilometers or 3,200 miles across). North is up. The image appears slightly grainy because it was re-projected to a scale of 6 kilometers (4 miles) per pixel. Scale in the original image was 15 kilometers (9 miles) per pixel. This view consists of an average of three images taken using a filter sensitive to near-infrared light centered at 938 nanometers, which allows for detection of Titan's surface and lower atmosphere, plus an image taken using a filter sensitive to visible light centered at 619 nanometers. The images were taken with the Cassini spacecraft's narrow-angle camera at a distance of approximately 2.5 million kilometers (1.6 million miles) from Titan and at a sun-Titan-spacecraft, or phase, angle of 56 degrees."

Recurrent novas
RS Ophiuchi (RS Oph) is a recurrent nova system approximately 5,000 light-years away in the constellation Ophiuchus. In its quiet phase it has an apparent magnitude of about 12.5. It erupted in 1898, 1933, 1958, 1967, 1985, and 2006 and reached about magnitude 5 on average. The recurrent nova is produced by a white dwarf star and a red giant circling about each other in a close orbit. About every 20 years, enough material from the red giant builds up on the surface of the white dwarf to produce a thermonuclear explosion. The white dwarf orbits close to the red giant, with an accretion disc concentrating the overflowing atmosphere of the red giant onto the white dwarf. If the white dwarf accretes enough mass to reach the Chandrasekhar limit, about 1.4 solar mass, it may explode as a Type Ia supernova.

Biology
An evolutionary radiation is an increase in taxonomic diversity or morphological disparity, due to adaptive change or the opening of ecospace. Radiations may affect one clade or many, and be rapid or gradual; where they are rapid, and driven by a single lineage's adaptation to their environment, they are termed adaptive radiations.

Perhaps the most familiar example of an evolutionary radiation is that of [Eutheria] placental mammals immediately after the extinction of the dinosaurs at the end of the Cretaceous, about 65 million years ago. At that time, the placental mammals were mostly small, insect-eating animals similar in size and shape to modern shrews. By the Eocene (58–37 million years ago), they had evolved into such diverse forms as bats, whales, and horses.

The Hawaiian lobelioids are a group of flowering plants in the [Campanula] bellflower family, Campanulaceae, all of which are endemic to the Hawaiian Islands. This is the largest plant radiation in the Hawaiian Islands, and indeed the largest on any island archipelago, with over 125 species.

Dose equivalents
The equivalent dose to a tissue is found by multiplying the absorbed dose, in gray, by a weighting factor (WR). The relation between absorbed dose D and equivalent dose H is thus:


 * $$H = W_R \cdot D$$.

The weighting factor (sometimes referred to as a quality factor) is determined by the radiation type and energy range.


 * $$H_T = \sum_R W_R \cdot D_{T,R}\ ,$$

where
 * HT is the equivalent dose absorbed by tissue T
 * DT,R is the absorbed dose in tissue T by radiation type R
 * WR is the weighting factor defined by the following table

Thus for example, an absorbed dose of 1 Gy by alpha particles will lead to an equivalent dose of 20 Sv. The maximum weight of 30 is obtained for neutrons with L = 100 keV/&mu;m.

Effective doses
The effective dose of radiation (E), absorbed by a person is obtained by averaging over all irradiated tissues with weighting factors adding up to 1:


 * $$E = \sum_T W_T \cdot H_T = \sum_T W_T \sum_R W_R \cdot D_{T,R}$$.

Grays
The gray (symbol: Gy) is the SI derived unit of absorbed radiation dose of ionizing radiation (for example, X-rays), and is defined as the absorption of one joule of ionizing radiation by one kilogram of matter (usually human tissue). The rad is equivalent to 0.01 Gy.

One gray is the absorption of one joule of energy, in the form of ionizing radiation, per kilogram of matter.


 * $$1 \ \mathrm{Gy} = 1\ \frac{\mathrm{J}}{\mathrm{kg}} = 1\ \mathrm{m}^2\cdot\mathrm{s}^{-2}$$

For X rays and gamma rays, these are the same units as the sievert (Sv). For alpha particles one sievert is twenty gray. To avoid any risk of confusion between the absorbed dose (by matter) and the equivalent dose (by biological tissues), one must use the corresponding special units, gray is used instead of the joule per kilogram for absorbed dose and the sievert instead of the joule per kilogram for the dose equivalent. The word "gray" is both the singular and plural spelling.

Chemistry
Many of the radiation effects on materials are produced by collision cascades and covered by radiation chemistry.

Radiation chemistry is a subdivision of nuclear chemistry which is the study of the chemical effects of radiation on matter; this is very different from radiochemistry as no radioactivity needs to be present in the material which is being chemically changed by the radiation.

Radiochemistry is the chemistry of radioactive materials, where radioactive isotopes of elements are used to study the properties and chemical reactions of non-radioactive isotopes (often within radiochemistry the absence of radioactivity leads to a substance being described as being inactive as the isotopes are stable). Much of radiochemistry deals with the use of radioactivity to study ordinary chemical reactions. This is very different from radiation chemistry since the radiation levels are kept too low to influence the chemistry.

Nuclear chemistry is the subfield of chemistry dealing with radioactivity, nuclear processes and nuclear properties. It is the chemistry of radioactive elements such as the actinides, radium and radon together with the chemistry associated with equipment (such as nuclear reactors) which are designed to perform nuclear processes. This includes the corrosion of surfaces and the behavior under conditions of both normal and abnormal operation (such as during an accident). An important area is the behavior of objects and materials after being placed into a nuclear waste storage or disposal site.

Geography
A geographical area is regarded as a natural environment.

A species flock may arise when a species penetrates a new geographical area and diversifies to occupy a variety of ecological niches; this process is known as adaptive radiation. The first species flock to be recognized as such was the 13 species of Darwin's finches on the Galápagos Islands described by Charles Darwin.

Solar radiation increases significantly as the atmosphere gets thinner with increasing altitude thereby absorbing less ultraviolet radiation. Snow cover reflecting the radiation can amplify the effects by up to 75% increasing the risks and damage from sunburn and snow blindness.

Ionization of the ionosphere depends primarily on the Sun and its activity. The amount of ionization in the ionosphere varies greatly with the amount of radiation received from the Sun. Thus there is a diurnal (time of day) effect and a seasonal effect. The local winter hemisphere is tipped away from the Sun, thus there is less received solar radiation. The activity of the Sun is associated with the sunspot cycle, with more radiation occurring with more sunspots. Radiation received also varies with geographical location (polar, auroral zones, mid-latitudes, and equatorial regions).

Geology
Granite is a natural source of radiation, like most natural stones. However, some granites have been reported to have higher radioactivity thereby raising some concerns about their safety.

Some granites contain around 10 to 20 parts per million of uranium. By contrast, more mafic rocks such as tonalite, gabbro or diorite have 1 to 5 PPM uranium, and limestones and sedimentary rocks usually have equally low amounts. Many large granite plutons are the sources for palaeochannel-hosted or roll front uranium ore deposits, where the uranium washes into the sediments from the granite uplands and associated, often highly radioactive, pegmatites. Granite could be considered a potential natural radiological hazard as, for instance, villages located over granite may be susceptible to higher doses of radiation than other communities. Cellars and basements sunk into soils over granite can become a trap for radon gas, which is formed by the decay of uranium. Radon gas poses significant health concerns, and is the number two cause of lung cancer in the US behind smoking.

Thorium occurs in all granites as well. Conway granite has been noted for its relatively high thorium concentration of 56 (±6) PPM.

Ancient history
The ancient history period dates from around 8,000 to 3,000 b2k.

Meteorites and lunar rocks may contain a record of the ancient radiation history of various stars including our own solar system.

The Explorer 3 spacecraft was spin-stabilized and had an on-board tape recorder to provide a complete radiation history for each orbit.

The Plutonium Files: America's Secret Medical Experiments in the Cold War is a 1999 book by Eileen Welsome. It is a history of U.S. government-engineered radiation experiments on unwitting Americans, based on the Pulitzer Prize–winning series Welsome wrote for The Albuquerque Tribune.

With their closest relatives, the Maluridae (Australian fairy-wrens), Pardalotidae (pardalotes), and Acanthizidae (thornbills, Australian warblers, scrubwrens, etc.) [the honeyeaters] comprise the superfamily Meliphagoidea and originated early in the evolutionary history of the oscine passerine radiation.

Mathematics
The Sakuma–Hattori equation is a mathematical model for predicting the amount of thermal radiation, radiometric flux or radiometric power emitted from a perfect blackbody or received by a thermal radiation detector.

In its general form it looks like:
 * $$S(T) = \frac{C}{\exp\left(\frac{c_2}{\lambda _x T}\right)-1}$$

where:

The Stokes parameters are a set of values that describe the polarization state of electromagnetic radiation.

The relationship of the Stokes parameters to intensity and polarization ellipse parameters is shown in the equations below and the figure at right.


 * $$ \begin{align}

S_0 &= I \\ S_1 &= p I \cos 2\psi \cos 2\chi\\ S_2 &= p I \sin 2\psi \cos 2\chi\\ S_3 &= p I \sin 2\chi. \end{align} $$

Here $$p I$$, $$2\psi$$ and $$2\chi$$ are the spherical coordinates of the three-dimensional vector of cartesian coordinates$$(S_1, S_2, S_3)$$. $$I$$ is the total intensity of the beam, and $$p$$ is the degree of polarization. The factor of two before $$\psi$$ represents the fact that any polarization ellipse is indistinguishable from one rotated by 180°, while the factor of two before $$\chi$$ indicates that an ellipse is indistinguishable from one with the semi-axis lengths swapped accompanied by a 90° rotation. The four Stokes parameters are sometimes denoted I, Q, U and V, respectively.

If given the Stokes parameters one can solve for the spherical coordinates with the following equations:


 * $$ \begin{align}

I &= S_0 \\ p &= \frac{\sqrt{S_1^2 + S_2^2 + S_3^2}}{S_0} \\ 2\psi &= \mathrm{atan} \frac{S_2}{S_1}\\ 2\chi &= \mathrm{atan} \frac{S_3}{\sqrt{S_1^2+S_2^2}}.\\ \end{align}$$

Physics
A particle on the exact design trajectory (or design orbit) of the accelerator only experiences dipole field components, while particles with transverse position deviation $$\scriptstyle x(s)$$ are re-focused to the design orbit. For preliminary calculations, neglecting all fields components higher than quadrupolar, an inhomogenic Hill differential equation


 * $$ \frac{d^2}{ds^2}\,x(s) + k(s)\,x(s) = \frac{1}{R} \, \frac{\Delta p}{p} $$

can be used as an approximation, with
 * a non-constant focusing force $$\scriptstyle k(s)$$, including strong focusing and weak focusing effects
 * the relative deviation from the design beam impulse $$\scriptstyle \Delta p / p$$
 * the trajectory curvature radius $$\scriptstyle R$$, and
 * the design path length $$\scriptstyle s$$,

thus identifying the system as a parametric oscillator. Beam parameters for the accelerator can then be calculated using ray transfer matrix analysis; e.g., a quadrupolar field is analogous to a lens in geometrical optics, having similar properties regarding beam focusing (but obeying Earnshaw's theorem).

Roentgens
Def. the radiation exposure equal to the quantity of ionizing radiation that will produce one esu of charge in one cubic centimetre of dry air at 0 °C and a standard atmosphere is called a roentgen.

Using an air ionization energy of about 35 J/C, we have 1 Gy ≈ 111 R.

Technology
The RHPPC is a radiation hardened processor based on PowerPC 603e technology licensed from Motorola (now Freescale) and manufactured by Honeywell. The RHPPC is equivalent to the commercial PowerPC 603e processor with the minor exceptions of the phase locked loop (PLL) and the processor version register (PVR). The RHPPC processor is compatible with the PowerPC architecture (Book I-III), the PowerPC 603e programmers interface and is also supported by common PowerPC software tools and embedded operating systems, like VxWorks.

Demron is a radiation-blocking fabric made by Radiation Shield Technologies. The material is said to have radiation protection similar to lead shielding, while being lightweight and flexible. The composition of Demron is proprietary, but is described as a non-toxic polymer. According to its manufacturer, while Demron shields the wearer from radiation alone, it can be coupled with different protective materials to block chemical and biological threats as well. Demron is roughly three to four times more expensive than a conventional lead apron, but can be treated like a normal fabric for cleaning, storage and disposal. More recent uses for Demron include certified first responder hazmat suits as well as tactical vests. Demron is proven by the United States Department of Energy to significantly reduce high energy alpha and beta radiation, and reduce low energy gamma radiation. When several sheets of Demron are laminated together the result is a much more powerful shield, though Demron cannot completely block all gamma radiation.

Protection
Radiation protection, sometimes known as radiological protection, is the protection of people and the environment from the harmful effects of ionizing radiation, which includes both particle radiation and high energy electromagnetic radiation. [Ionizing radiation] causes microscopic damage to living tissue, resulting in skin burns and radiation sickness at high exposures and statistically elevated risks of cancer, tumors and genetic damage at low exposures. There are three factors that control the amount, or dose, of radiation received from a source. Radiation exposure can be managed by a combination of these factors:
 * 1) Time : Reducing the time of an exposure reduces the effective dose proportionally.  An example of reducing radiation doses by reducing the time of exposures might be improving operator training to reduce the time they take to handle a source.
 * 2) Distance : Increasing distance reduces dose due to the inverse square law.  Distance can be as simple as handling a source with forceps rather than fingers.
 * 3) Shielding : The term 'biological shield' refers to a mass of absorbing material placed around a reactor, or other radioactive source, to reduce the radiation to a level safe for humans.

Gloveboxes
A glovebox (or glove box) is a sealed container that is designed to allow one to manipulate objects where a separate atmosphere is desired. Built into the sides of the glovebox are gloves arranged in such a way that the user can place their hands into the gloves and perform tasks inside the box without breaking containment. Part or all of the box is usually transparent to allow the user to see what is being manipulated. Two types of gloveboxes exist: one allows a person to work with hazardous substances, such as radioactive materials or infectious disease agents; the other allows manipulation of substances that must be contained within a very high purity inert atmosphere, such as argon or nitrogen. It is also possible to use a glovebox for manipulation of items in a vacuum chamber. Gloveboxes used for hazardous materials generally are maintained at a lower pressure than the surrounding atmosphere, so that microscopic leaks result in air intake rather than hazard outflow. Gloveboxes used for hazardous materials generally incorporate HEPA filters into the exhaust, to keep the hazard contained.

Shield effectiveness
The effectiveness of a material as a biological shield is related to its cross-section for scattering and absorption, and to a first approximation is proportional to the total mass of material per unit area interposed along the line of sight between the radiation source and the region to be protected. Hence, shielding strength or "thickness" is conventionally measured in units of g/cm2. The radiation that manages to get through falls exponentially with the thickness of the shield. In X-ray facilities, the plaster on the rooms with the x-ray generator contains barium sulfate and the operators stay behind a leaded glass screen and wear lead aprons. Almost any material can act as a shield from gamma or x-rays if used in sufficient amounts.

Practical radiation protection tends to be a job of juggling the three factors to identify the most cost effective solution.

Hypotheses

 * 1) Radiation has a continuum of speeds.