All articles starting with R
22,461 articles
Radiation proctitis
Radiation proctitis, also called radiation proctopathy, is rectal mucosal injury from pelvic radiation therapy for prostate, rectal, cervical, or anal cancer; about 75% develop the acute form and roughly 1-20% the chronic bleeding form.
Radiation protection
Radiation protection, also known as radiological protection, is the science and practice of protecting people and the environment from ionizing radiation, organized around justification, optimization, and dose limitation.
Radiation reaction and energy balance in post-Newtonian theory
Radiation reaction in post-Newtonian theory is a dissipative force appearing at the 2.5PN order, linking lost energy and angular momentum to gravitational wave fluxes, observed in binary pulsars.
Radiation research
Radiation research studies radiation effects in physics, chemistry, biology, and medicine; Radiation Research (Radiat. Res., ISSN 0033-7587) is the Radiation Research Society's journal, published since 1954, distinct from the Japanese Journal of Radiation Research.
Radiation retinopathy
Radiation retinopathy, also called radiation-induced retinopathy, is a progressive occlusive retinal vasculopathy after ocular or periocular radiotherapy, most often plaque brachytherapy for uveal melanoma, causing ischemia, macular edema, and vision loss.
Radiation segmentectomy
Radiation segmentectomy is a liver-directed radioembolization technique that delivers ablative yttrium-90 microsphere doses to one or two hepatic segments, most often to treat solitary hepatocellular carcinoma.
Radiation shielding
Radiation shielding is the placement of attenuating material between a source of ionizing radiation and people or equipment, designed so dose rates beyond the shield are acceptable.
Radiation therapy
Radiation therapy (radiotherapy, irradiation): cancer treatment using high-energy x-rays, gamma rays, protons, or radioactive sources to damage tumor DNA. Delivered as external beam, brachytherapy, or systemic therapy; main risk is normal-tissue toxicity.
Radiation thermometry
Radiation thermometry measures an object's temperature without physical contact by analyzing its emitted thermal radiation; converting radiance temperature to true temperature requires knowing the surface's emissivity, the field's central problem.
Radiation trapping
Radiation trapping, also called resonance imprisonment, is the process in which an emitted photon is repeatedly absorbed and re-emitted by atoms of the same gas before escaping.
Radiation treatment planning
Radiation treatment planning, also called forward planning, is the process of designing a radiation therapy course: imaging the patient, outlining targets, and optimizing beam arrangements and doses.
Radiation-dominated era
The radiation-dominated era is the period of cosmic history, from the Big Bang until roughly 50,000 years after it, when radiation's energy density exceeded matter's and controlled the universe's expansion, ending at matter-radiation equality.
Radiation-induced brain injury
Radiation-induced brain injury (ICD-11 8E61.0), also called post-radiation brain injury or cerebral radionecrosis, is brain damage from therapeutic cranial irradiation, divided into acute, early-delayed, and late-delayed syndromes, causing cognitive impairment and necrosis in long-term survivors.
Radiation-induced colitis
Radiation-induced colitis (放射線誘発性大腸炎, ICD-11 DB33.41) is radiation-therapy-caused colonic mucosal inflammation, acute within 60 days or chronic after months to years, dose-dependent above roughly 45–70 Gy.
Radiation-induced Moyamoya syndrome
Radiation-induced moyamoya syndrome (RIMS): moyamoya vasculopathy after cranial radiotherapy, mainly in children irradiated for optic pathway glioma or craniopharyngioma; median latency about 40 months, dose- and NF-1-dependent risk, treated by revascularization.
Radiation-induced plexopathy
Radiation-induced plexopathy (RIBP, RILSP) is rare progressive damage to the brachial or lumbosacral nerve plexus after cancer radiotherapy, appearing months to decades later; typically painless, often bilateral, with fibrosis and no proven disease-modifying treatment.
Radiation-induced swelling
Radiation-induced swelling is the increase in volume of irradiated metals and alloys, caused by voids forming from radiation-produced vacancies; first reported in 1967 from Dounreay Fast Reactor cladding.
Radiation-induced valvular heart disease
Radiation-induced valvular heart disease is calcification and dysfunction of heart valves, usually aortic and mitral, caused by chest radiation therapy, appearing a median 23 years later.
Radiative cooling
Radiative cooling is a passive cooling method in which an object dumps heat to outer space by emitting infrared radiation through the atmosphere's 8–13 µm transparency window.
Radiative efficiency
Radiative efficiency is the fraction of accreted matter's rest-mass energy that a black hole converts into radiation, rising from about 0.06 for non-spinning holes to 0.42 for maximally spinning ones.
Radiative equilibrium
Radiative equilibrium is the state of a planetary atmosphere in which net radiative heating is zero at every level, first formulated by Karl Schwarzschild in 1906.
Radiative forcing
Radiative forcing, also called climate forcing, is the change in Earth's energy balance from an external driver such as carbon dioxide, measured in watts per square meter.
Radiative heat transfer
Radiative heat transfer is the exchange of energy by electromagnetic radiation, analyzed through geometry-based view factors for transparent media and the radiative transfer equation for participating media.
Radiative improved mode
The radiative improved mode (RI mode) is a tokamak plasma regime, discovered on ISX-B and studied on TEXTOR-94, where noble gas impurity injection improves energy confinement.
Radiative recombination
Radiative recombination is the capture of a free electron by an atomic ion into a bound state, with a photon carrying away the excess energy; it is the inverse of photoionization.
Radiative transfer
Radiative transfer, also called radiation transport, describes how radiation propagates through a medium that absorbs, emits, and scatters it; its governing equation underlies stellar atmospheres, atmospheric physics, and remote sensing.
Radiative zone
The radiative zone is the layer of the Sun's interior between the core and the convection zone, where energy travels outward as photons over more than 170,000 years.
Radiator
A radiator, also called an automobile or car radiator when fitted to vehicles, is a device that transfers heat from a hot fluid to its surroundings, used in buildings, vehicle engines, and spacecraft.
Radiator Building—Night, New York
Radiator Building—Night, New York is a 1927 oil painting by Georgia O'Keeffe showing the American Radiator Building in Midtown Manhattan as a black skyscraper lit by windows, steam, and searchlights.
Radiator panel (spacecraft)
A radiator panel is an external spacecraft surface that rejects waste heat by thermal radiation, connected to heat sources through heat pipes, pumped fluid loops, or thermal straps.