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Isotopes of silicon
The isotopes of silicon are 23 nuclear species, with three stable isotopes, silicon-28, silicon-29, and silicon-30, occurring naturally and silicon-28 making up over 92 percent.
Isotopes of sodium
Isotopes of sodium are the nuclear species of sodium, all with 11 protons and varying neutrons. Only sodium-23 is stable; the heaviest, sodium-39, was discovered in 2022.
Isotopes of tellurium
Tellurium (atomic number 52) has eight naturally occurring isotopes, of which three are radioactive with such long half-lives that tellurium behaves as if stable in most settings.
Isotopes of uranium
Isotopes of uranium are varieties of the element that differ in neutron number. Natural uranium is almost all uranium-238, with fissile uranium-235 and synthetic isotopes like uranium-233 and uranium-236.
Isotopes of xenon
Naturally occurring xenon consists of nine isotopes with mass numbers 124 through 136, six of which are stable and three of which decay extremely slowly.
Isotopic abundance
Isotopic abundance is the relative number of atoms of a particular isotope among all atoms of an element, and it determines that element's atomic weight.
Isotopic fractionation
Isotopic fractionation is the partitioning of heavy versus light isotopes of an element between two phases or reaction products during physical, chemical, or biological processes.
Isotopic signature
An isotopic signature is the characteristic pattern of stable isotope ratios in a material, set by physical, chemical, and biological processes, used to trace origin and history.
Isotopic tracing
Isotopic tracing is an analytical method that tracks atoms and molecules by labeling them with detectable isotopes such as 13C or 2H, revealing metabolic pathways, reaction directionality, and flux.
Isotopically enriched silicon
Isotopically enriched silicon is silicon with silicon-28 raised above its natural abundance, mainly by removing silicon-29, whose nuclear spin causes quantum decoherence, making it an ideal host material for semiconductor quantum computing.
Isotopologue
An isotopologue is a molecular entity that differs from another only in its isotopic composition, meaning the number of isotopic substitutions, as in the series CH₄, CH₃D, and CH₂D₂.
Isotopomer
An isotopomer, short for isotopic isomer, is one of a set of isomers that share the same number of each isotopic atom but differ in label position.
Isotropic coordinates
Isotropic coordinates are coordinates for the Schwarzschild solution of general relativity in which the spatial metric is conformal to flat Euclidean space, with the horizon at radius m/2.
Isotropy
Isotropy is the property of being identical in all directions: a material, field, or space is isotropic when its properties do not depend on the direction measured, with anisotropy as its opposite.
Isoxazole
Isoxazole (1,2-oxazole) is a five-membered aromatic heterocycle, formula C₃H₃NO, with adjacent oxygen and nitrogen atoms, distinguished from oxazole by the 1,2 heteroatom placement and used as a drug scaffold and synthetic intermediate.
Isradipine
Isradipine is a dihydropyridine calcium channel blocker used to treat high blood pressure, alone or with thiazide diuretics; a large trial found it did not slow early Parkinson disease.
Israel E. Wachs
Israel E. Wachs is an American chemical engineer at Lehigh University known for pioneering operando spectroscopy of catalysts and elected to the National Academy of Engineering in 2026.
Israel Gelfand
Israel Gelfand (1913–2009) was a Soviet and American mathematician who founded the theory of commutative Banach algebras and built one of the twentieth century's most influential mathematical schools.
ISS-CREAM
ISS-CREAM (Cosmic Ray Energetics And Mass for the International Space Station) is a cosmic-ray detector mounted outside the ISS, launched in August 2017 to measure elemental composition and energy spectra of high-energy cosmic rays.
Issai Schur
Issai Schur (1875–1941) was a German mathematician and founder of the Berlin School of algebra, a pioneer of group representation theory known for Schur's lemma and the Schur multiplier.
Istituto Nazionale di Statistica
The Istituto Nazionale di Statistica (Istat), Italy's National Institute of Statistics, is a public research institute founded in 1926 that produces the country's official statistics from Rome.
Istituto Superiore per la Protezione e la Ricerca Ambientale
The Istituto Superiore per la Protezione e la Ricerca Ambientale (ISPRA) is Italy's national public research institute for environmental protection and research, established in 2008.
István Fáry
István Fáry (1922–1984) was a Hungarian mathematician and UC Berkeley professor of geometry and topology, known for Fáry's theorem on straight-line drawings of planar graphs and the Fáry–Milnor theorem on knots.
It from bit
"It from bit" is the thesis coined by American physicist John Archibald Wheeler in 1989 that every physical thing derives its significance from bits, the binary yes-or-no answers elicited by measurement.
itabirite
Itabirite is a laminated, metamorphosed banded iron formation in Minas Gerais, Brazil, named there in 1822, composed of quartz with hematite or magnetite and hosting most Brazilian iron ore.
Itaconic acid
Itaconic acid (methylenesuccinic acid) is an unsaturated dicarboxylic acid, C₅H₆O₄, made by fermenting sugars with the fungus Aspergillus terreus and used as a monomer for polymers, resins, and superabsorbents.
Itai Cohen
Itai Cohen is a soft-matter physicist and Professor of Physics at Cornell University whose group studies shear-thickening suspensions, origami metamaterials, insect flight, and micrometer-scale robots, holding the record for the smallest walking robot.
Italian National Institute for Nuclear Physics
The Italian National Institute for Nuclear Physics (Istituto Nazionale di Fisica Nucleare, INFN) is Italy's public research institute for nuclear, subnuclear, and astroparticle physics, founded in 1951.
Italian Physical Society
The Italian Physical Society (Società Italiana di Fisica, SIF) is the national learned society of Italian physicists, founded in 1897 in Bologna around the journal Il Nuovo Cimento.
Italian six-hour clock
The Italian six-hour clock is a clock dial with Roman numerals I to VI, used with Italian time reckoning, in which the hand circles four times a day.