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In the physical sciences, a particle is a small localized object to which can be ascribed several physical properties such as volume or mass. The word is rather general in meaning, and is refined as needed by various scientific fields.

or negligible, or if The term “particle� geometrical properis usually applied ties and structure differently to three are irrelevant, then class it can be considof sizes. The term ered a particle. For macroscopic partiexample, grains of cle, usually refers to sand on a beach particles much larger can be considered than atoms and particles because molecules. the size of one grain These are usually of sand (c. 1 mm) is abstracted as pointnegligible compared like particles, to the beach, and the even thoughthey features of individual have volumes, Whether objects grains of sand are shapes, structures, usually irrelevant to etc. Examples of can be considered particles depends on the problem at hand. macroscopic parthe scale of the conticles would include text; if an object’s dust, sand, pieces own size is small of debris during a car accident or even objects as big as the stars of a galaxy.


Another type, microscopic particles usually refers to particles of sizes ranging from atoms to molecules, such as carbon dioxide, nanoparticles, and colloidal particles. The smallest of particles are the subatomic particles, which refer to particles smaller than atoms. These would include particles such as the constituents of atoms

– protons, neutrons, and electron – as well as other types of particles which can only be produced in particle accelerators or cosmic rays.


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ucked have ever been pl to t me co a of part of the e the first pieces e collection was Th h. The particles ar rt Ea to ed samand return (NASA) Stardust ’s on ti ra st from outer space ni mi Ad goal utics and Space 1999. The primary ry ua br National Aerona Fe in ed s during its n which launch on-based sample rb ple return missio ca d an st nisdu t to collec sample-return ca st du ar St e of Stardust was Th 2. llowing r with Comet Wild Utah on Jan. 15, fo of s at closest encounte fl lt sa rt s of onto the dese with it thousand ng gi in br s, ter parachuted le mi ly three million em. a journey of near of the solar syst ge ed e th om fr s particle


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Nuclear Physics The overarching goal, which is pursued in several distinct ways, is to find and understand what physics may lie beyond the standard model. There are several powerful experimental reasons to expect new physics, including dark matter and neutrino mass. There are also theoretical hints that this new physics should be found at accessible energy scales. Furthermore, there may be unexpected and unpredicted surprises that will give us the most opportunity to learn about nature.

In nuclear physics and nuclear chemistry, nuclear fission refers to either a nuclear reaction or a radioactive decay process in which the nucleus of an atom splits into smaller parts (lighter nuclei), often producing free neutrons and photons (in the form of gamma rays), and re-

First Beam Collision

leasing a very large amount of energy, even by the energetic standards of radioactive decay. The two

nuclei produced are most often of comparable but slightly different sizes, typically with a mass ratio of products of about 3 to 2, for common fissile isotopes. Most fissions are binary fissions (producing two charged fragments), but occasionally (2 to 4 times per 1000 events), three positively charged fragments are produced, in a ternary fission. The smallest of these fragments in ternary processes ranges in


Cosmic dust is a type of dust composed of particles in space which are a few molecules to 0.1 Âľm in size. Cosmic dust can be further distinguished by its astronomical location; for example: intergalactic dust, interstellar dust, interplanetary dust (such as in the zodiacal cloud) and circumplanetary dust (such as in a planetary ring). In our own Solar System, interplanetary dust causes the zodiacal light. Sources include comet dust, asteroidal dust, dust from the Kuiper belt, and interstellar dust passing through our solar system. The terminology has no specific applica-


tion for describing materials found on the planet Earth, other than in the most general sense that all elements with an atomic number higher than helium are believed to be formed in the core of stars via stellar nucleosynthesis and supernova nucleosynthesis events. As such all elements that exist can be indiscriminately considered to be a form of “cosmic dust.” In October 2011, scientists reported that cosmic dust contains complex organic matter (“amorphous organic solids with a mixed aromaticaliphatic structure”) that could be created naturally, and rapidly, by stars.


Particle zine one