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Cosmogenic Activation

The cosmogenic activation of materials is the production of radioactive isotopes due to the exposure to cosmic rays. On the Earth's surface, spallation induced by cosmic neutrons is responsible of most of the activation, but other reactions and cosmic ray components must be considered too in other conditions, like if materials are flown at high altitudes or stored deep underground. Cosmogenic activation is relevant in different contexts; for example, together with primordial or anthropogenic radioactivity, it s a background source in experiments devoted to the investigation of rare event phenomena, like the direct detection of dark matter particles or the nuclear double beta decay.

1.5K
26 Oct 2020

Topic Review

Cosmic-ray Sources - Black Holes

Cosmic rays were discovered over one hundred years ago but there are still unsolved problems. One of the hot problems is the origin of cosmic rays of the highest energies. Sources are still unclear and it is neither clear how particles gain ultra-high energies. Possible sources of cosmic rays at the highest energies are supermassive black holes. From this perspective we discuss in a popular form some recent developments in cosmic ray studies along with author’s recent results.The paper also offers materials for further reading.

961
21 Jan 2021

Topic Review

Corvus, Latin for "crow" or "raven," is a small but distinct constellation visible in the southern celestial hemisphere. Its shape is reminiscent of a bird in flight, featuring four bright stars that form the outline of a celestial crow. In ancient mythology, Corvus is associated with various tales, often depicted as a messenger bird serving the gods.

468
08 Mar 2024

Topic Review

COROT-7b (previously named COROT-Exo-7b) is an exoplanet orbiting around the star COROT-7, in the constellation Monoceros, at 489 light years from Earth. It was first detected photometrically by the French-led COROT mission and reported in February 2009. Until the announcement of Kepler-10b in January 2011, it was the smallest exoplanet to have its diameter measured, at 1.58 times that of the Earth (which would give it a volume 3.95 times Earth's), and the first potential extrasolar terrestrial planet to be found. The planet has a very short orbital period, revolving around its host star in about 20 hours. Combination of the planet's diameter derived from transit data with the planet's mass derived from radial velocity measurements, meant that the density of CoRoT-7b was about the same as that of Earth and, therefore, that CoRoT-7b was made of rock like Earth and was not a gas giant like Jupiter. The radial velocity observations of CoRoT-7 also detected a second super-Earth, CoRoT-7c, which has a mass 8.4 times that of Earth and orbits every 3.7 days at a distance of 6.9 million km (4.3 million miles).

1.3K
19 Oct 2022

Topic Review

A coronal cloud is the cloud of hot plasma gas surrounding a coronal mass ejection. It is usually made up of protons and electrons. When a coronal mass ejection occurs at the Earth's Sun, it is the coronal cloud that usually reaches Earth and causes damage to electrical equipment and space satellites, not the ejection or flare itself. The damage is mostly the result of the high amount of electricity moving through the atmosphere. A coronal cloud is released when a solar flare becomes a coronal mass ejection; the coronal cloud often contains more radioactive particles than the mass ejection itself. A coronal mass ejection occurs when a solar flare becomes so hot that it snaps and breaks in two, becoming a "rope" of heat and magnetism that stretches between two sunspots. The resulting coronal mass ejection can be compared to a horseshoe magnet, the sunspots being the poles and the oscillating magnetic connector the handle. Coronal mass ejections typically do not last very long, because they cool down as the coronal cloud of gas is released and begins to hurtle away from the Sun.

414
07 Oct 2022

Topic Review

A coronagraph is a telescopic attachment designed to block out the direct light from a star so that nearby objects – which otherwise would be hidden in the star's bright glare – can be resolved. Most coronagraphs are intended to view the corona of the Sun, but a new class of conceptually similar instruments (called stellar coronagraphs to distinguish them from solar coronagraphs) are being used to find extrasolar planets and circumstellar disks around nearby stars as well as host galaxies in quasars and other similar objects with active galactic nuclei (AGN).

559
23 Nov 2022

Topic Review

Corona Borealis

Corona Borealis, Latin for "Northern Crown," is a constellation in the northern celestial hemisphere, known for its distinctive semicircular shape resembling a crown. Its counterpart in the southern hemisphere, Corona Australis, shares a similar name and mythological association with crowns but lies on the opposite side of the celestial sphere.

390
08 Mar 2024

Topic Review

Corona Australis

Corona Australis, Latin for "Southern Crown," is a small constellation in the southern celestial hemisphere. Situated near the celestial equator, it represents a crown or wreath and is associated with various mythological interpretations across different cultures. Despite its modest size, Corona Australis contains several interesting celestial objects.

182
08 Mar 2024

Topic Review

A corona (meaning 'crown' in Latin derived from Ancient Greek 'κορώνη' (korōnè, “garland, wreath”)) is an aura of plasma that surrounds the Sun and other stars. The Sun's corona extends millions of kilometres into outer space and is most easily seen during a total solar eclipse, but it is also observable with a coronagraph. Spectroscopy measurements indicate strong ionization in the corona and a plasma temperature in excess of 1000000 kelvin, much hotter than the surface of the Sun. Light from the corona comes from three primary sources, from the same volume of space. The K-corona (K for kontinuierlich, "continuous" in German) is created by sunlight scattering off free electrons; Doppler broadening of the reflected photospheric absorption lines spreads them so greatly as to completely obscure them, giving the spectral appearance of a continuum with no absorption lines. The F-corona (F for Fraunhofer) is created by sunlight bouncing off dust particles, and is observable because its light contains the Fraunhofer absorption lines that are seen in raw sunlight; the F-corona extends to very high elongation angles from the Sun, where it is called the zodiacal light. The E-corona (E for emission) is due to spectral emission lines produced by ions that are present in the coronal plasma; it may be observed in broad or forbidden or hot spectral emission lines and is the main source of information about the corona's composition.

490
08 Nov 2022

Topic Review

Corium (Nuclear Reactor)

Corium, also called fuel-containing material (FCM) or lava-like fuel-containing material (LFCM), is a material that is created in the core of a nuclear reactor during a meltdown accident. It resembles natural lava in its consistency. It consists of a mixture of nuclear fuel, fission products, control rods, structural materials from the affected parts of the reactor, products of their chemical reaction with air, water and steam, and, in the event that the reactor vessel is breached, molten concrete from the floor of the reactor room.

738
28 Oct 2022

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