#nuclear

• Actinide — A metallic and radioactive chemical element belonging to the actinide (or actinoid) series, a stabilized structural group of 15 heavy elements located in the periodic table from actinium (atomic number 89) to lawrencium (atomic number 103). All these elements belong to the 'f' block (5f series) of transition metals, characterized by high nuclear instability, high density, and electrochemical properties closely correlated with those of actinium.
• Actinides — Plural form for the neuter noun 'actinid'; a homogeneous structural group in the periodic table consisting of 15 metallic and radioactive chemical elements, with atomic numbers ranging from 89 (actinium) to 103 (lawrencium). Located in the 'f' block of transition elements in the 7th period, they exhibit similar chemical properties due to the progressive filling of the 5f electron subshell, being recognized for their high density, substantial nuclear instability, and capacity to undergo fission.
• Actinium — The original neological form, Latin spelling, and official international English name for the chemical element 'actiniu' (symbol Ac, atomic number 89). This structural term defines the heavy radioactive metal in the 'f' block of the periodic table, used within global scientific literature and IUPAC standards to describe the properties of isotopes involved in nuclear fission processes or advanced oncological medical research.
• Actinogenesis — A physical process, natural or artificial, through which rays or radiations are generated, produced, and emitted, particularly within the short-wave electromagnetic spectrum, such as ultraviolet radiation, X-rays, or gamma rays. This structural phenomenon constitutes a subject of study in nuclear physics and radiology, being essential for understanding the emission mechanisms of radiant sources, celestial bodies, or technological devices used in industrial medical imaging.
• Actinon — A historical and scientific term used to designate the radioactive isotope radon-219 (An), a structural intermediate product within the natural decay chain of actinium or uranium-235. It is a heavy, unstable noble gas with an extremely short half-life of approximately 3.96 seconds, emitting high-energy alpha particles before transforming into polonium-215, monitored in nuclear research laboratories for the study of radioactive emanations.
• Activity — A set of physical, intellectual, or physiological acts, manifestations, or processes carried out consciously and systematically by a human being, a collectivity, or a system, with a specific purpose; the dynamic functioning of an organ or mechanism. In physics, it represents the number of nuclear disintegrations produced in a radioactive substance per unit of time.
• IAEA — Official Romanian acronym for the International Atomic Energy Agency (known globally by its English acronym IAEA), an autonomous organization within the United Nations system, founded in 1957 with its headquarters in Vienna. Its structural role is to promote the peaceful, safe, and exclusively civilian use of nuclear energy, implementing rigorous monitoring and inspection mechanisms to prevent the proliferation of atomic weapons.
• Americium — A synthetic, highly radioactive chemical element of the actinide series, with atomic number 95 and symbol Am. This silver-colored structural transuranium metal, originally obtained by bombarding plutonium with neutrons, is utilized in precision industrial applications, such as household smoke detectors and alpha radiation sources for laboratory analyses.
• Amitosis — A form of direct cell division occurring through the simple cleavage, strangulation, or fragmentation of the nucleus and cytoplasm, without the individualization of chromosomes and without the formation of the mitotic apparatus (spindle). This physiological structural mechanism is considered a rudimentary method of multiplication, being specific to certain aged, specialized, or pathological cells in higher organisms, as well as many lower unicellular organisms.
• Antineutrino — The antiparticle corresponding to the neutrino, characterized by an extremely small (nearly zero) mass, a neutral electric charge, and half-integer spin, possessing an opposite helicity (right-handed) compared to that of the neutrino. This subatomic entity is predominantly emitted during beta-minus decay processes, interacting with matter exclusively through the weak nuclear force and gravity, which makes it extremely difficult to detect.
• Antineutron — The antiparticle corresponding to the neutron, possessing exactly the same mass and spin, but characterized by an opposite baryon number and a magnetic moment of opposite sign relative to the neutron. Although globally electrically neutral, its internal structure is composed of antiquarks (two down antiquarks and one up antiquark), determining its specific annihilation behavior upon contact with ordinary baryonic matter.
• Antiparticle — An elementary particle that has exactly the same mass, lifetime, and spin as a corresponding particle of ordinary matter, but whose electric charges, quantum numbers, and magnetic moments have opposite mathematical signs. Upon direct contact between a particle and an antiparticle, the structural phenomenon of mutual annihilation occurs, converting their entire mass into energy in the form of high-frequency photons.
• Anuclear — Not related to a cellular nucleus or situated outside nuclear structures; a term used in molecular biology to describe phenomena, biochemical processes, or cytoplasmic components that occur independently of the direct control or physical presence of the nucleus.
• Heavy water — A form of water in whose structure the light hydrogen atoms (protium) are completely or highly replaced by its heavy isotope named deuterium (D₂O). This structural chemical compound is characterized by a higher density than ordinary water and is widely used in the nuclear industry as a neutron moderator and cooling agent in CANDU-type power reactors.
• Astatine — A highly unstable radioactive chemical element of the halogen group, with atomic number 85 and symbol At; it is the rarest naturally occurring element in the Earth's crust, produced only transiently through the decay of uranium and thorium, and due to its extremely short half-life (a maximum of 8.1 hours for its most stable isotope), its physical properties are studied almost exclusively through artificial synthesis techniques in particle accelerators.
• At — The official chemical symbol for the element astatine, an extremely rare and unstable radioactive halogen with atomic number 85. In modern periodic tables, At represents the heaviest characterized element in the halogen group, whose physical and chemical properties are theoretically deduced or microscopically observed in high-energy nuclear physics laboratories due to its very short half-life.
• Atomic — Pertaining to atoms, belonging to atoms, or utilizing the energy released by the fission or fusion of atomic nuclei. In a military and geopolitical context, the term describes weapons of mass destruction based on nuclear reactions, whereas in computer science and databases, it defines an indivisible operation that executes completely or not at all, guaranteeing system integrity.
• Atomoelectric — Pertaining to the production of electrical energy through the use of nuclear energy released during the fission of atoms; based on nuclear power plants. The term describes industrial infrastructures, equipment, or grids designed to transform heat generated by atomic reactors into high-power electric current.
• Autoradiograph — An image, photographic film, or structural digital record obtained through the autoradiography technique, which highlights the spatial distribution of radioactive substances or isotope-labeled molecules (tracers) previously introduced into a biological tissue, cell, or metallurgical material. The term also denotes the apparatus or technical detection assembly utilized in the laboratory to capture and visualize alpha, beta, or gamma radiation emissions originating directly from the analyzed sample.
• Autoradiography — A biophysical method of investigation and structural imaging consisting of detecting and recording the spatial distribution of radioactive substances or isotope-labeled molecules (tracers), by directly exposing the biological or metallurgical sample onto a photographic emulsion or a digital sensor. This experimental process utilizes the self-emission of radiation (alpha, beta, or gamma) from the sample to expose the contact medium, serving as a fundamental technique in nucleic acid mapping, cellular metabolism studies, and protein localization.