| RA | radioactive; ragocyte; ragweed antigen; rapidly adapting [receptors]; reactive arthritis; reciprocal... |
|---|---|
| RAIU | radioactive iodine uptake |
| RAMP | radioactive antigen microprecipitin; right atrial mean pressure |
| RAU | radioactive uptake |
| RI | radiation intensity; radioactive isotope; radioimmunology; recession index; recombinant inbred [stra... |
| impression material | Any substance or combination of substances used for making a negative reproduction or impression. (05 Mar 2000) |
|---|---|
| iodinated contrast material | A substance that contains iodine that can be injected, swallowed or given as an enema for the purpose of diagnostics. Iodinated contrast is radiopaque. This means that conventional X-rays will highlight the course of the contrast in the body. (27 Sep 1997) |
| type material | <zoology> A collective term for all type specimens. Zoologists should ensure that such material is transferred as quickly as possible to public institutions where their safety is guaranteed and they are accessible to other workers. (09 Jan 1998) |
| unconsolidated parent material | <ecology> Material from which a soil develops. (09 Oct 1997) |
| fertile material | <physics> In nuclear physics, this refers to a nuclide which converts to fissile material upon neutron capture and subsequent radioactive decay. Examples include Uranium-238 and Thorium-232. (09 Oct 1997) |
| fill material | Any material used for the primary purpose of replacing an aquatic area with dry land or of changing the bottom elevation of a waterbody. The term does not include any pollutant discharged into the water primarily to dispose of waste. (09 Oct 1997) |
| fissile material | <radiobiology> Material containing a large number of easily fissionable nuclei which give off multiple neutrons in the fission process. Usual meaning is that if a sufficiently large amount of fissile material is put together, a fission chain reaction can occur. Sometimes used synonymously with fissionable material, i.e., material that can be fissioned (though often under restricted circumstances, such as only with thermal (slow) neutrons). A more restricted meaning use of fissile material limits the concept to those materials which can be fissioned by neutrons of all energies (fast & slow). Examples include Uranium-235 and Plutonium-239. (09 Oct 1997) |
| air pollutants, radioactive | Pollutants, present in air, which exhibit radioactivity. (12 Dec 1998) |
| radioactive | Giving off radiation. (12 Dec 1998) |
| radioactive atom | <chemistry, physics> An atom with an unstable nucleus, which emits particulate or electromagnetic radiation (radioactive emission) to achieve greater stability. See: radionuclide, half-life, Becquerel. (05 Mar 2000) |
| radioactive constant | <physics, radiobiology> The fraction of the amount of a radionuclide that undergoes transition per unit time. Formally: Lamda=dP/dt Where dP is the probability of a given nucleus undergoing spontaneous nuclear transition in the time interval dt. (16 Dec 1997) |
| radioactive contamination | <radiobiology> Radioactive substance dispersed in material or places where it is undesirable. (16 Dec 1997) |
| radioactive cow | Colloquialism for radionuclide generator. See: cow. (05 Mar 2000) |
| radioactive decay | <physics> The process by which a spontaneous change in nuclear state takes place. This process is accompanied by the emission of energy in various specific combinations of electromagnetic and corpuscular radiation and neutrinos. (16 Dec 1997) |
| radioactive equilibrium | <radiobiology> That condition in which the activities of the members of a radioactive chain decrease exponentially in time with the half-life of the chain precursor. Such radioactive equilibrium is only possible when the half-life of the precursor is longer than that of any other chain member. If the precursor half-life is so long that the change in the precursor population during the period of interest can be ignored, all the activities become sensibly equal and the equilibrium is said to be secular, otherwise it is said to be transient. (16 Dec 1997) |