| alpha particle | <physics> A radioactive particle made up of two protons and two neutrons, these particles are created by the decay of a radioactive material or by nuclear bombardment, and they are the same as the nucleus of a helium-4 atom. (09 Oct 1997) |
|---|---|
| alpha particles | Positively charged particles composed of two protons and two neutrons, i.e., helium nuclei, emitted during disintegration of very heavy isotopes; a beam of alpha particles or an alpha ray has very strong ionizing power, but weak penetrability. (12 Dec 1998) |
| alpha-phenoxyethylpenicillin potassium | A penicillin preparation that is stable in gastric acid and is rapidly but only partially absorbed from the gastrointestinal tract. Synonym: alpha-phenoxyethylpenicillin potassium, penicillin B. (05 Mar 2000) |
| alpha-phenoxypropylpenicillin potassium | A semisynthetic acid-stable penicillin that may be more effective than penicillin G. Synonym: alpha-phenoxypropylpenicillin potassium. (05 Mar 2000) |
| alpha-pinene oxide lyase | <enzyme> From nocardia sp. Strain p18.3; catalyses the cleavage of both rings of the bicyclic structure with the formation of 2-methyl-5-isopropylhexa-2,5-dienal Registry number: EC 4.1.2.- Synonym: alpha-pinene oxide lyase (decyclizing) (26 Jun 1999) |
| alpha-prodine hydrochloride | See: alphaprodine. (05 Mar 2000) |
| alpha radiation | <physics, radiobiology> The most easily absorbable type of radiation, it consists of a stream of alpha particles, doubly ionised helium nuclei which are electrically charged and produce intense ionisation in matter. Alpha radiation can be deflected in electromagnetic fields. (09 Oct 1997) |
| alpha ray | <physics> A radioactive particle made up of two protons and two neutrons, these particles are created by the decay of a radioactive material or by nuclear bombardment, and they are the same as the nucleus of a helium-4 atom. (09 Oct 1997) |
| alpha rhythm | Brain waves in the encephalogram which have a frequency of 8 to 13 per second. They are typical of the normal person awake and in a quiet resting state, and occur principally in the occipital region. (12 Dec 1998) |
| alpha-ribazole | 1-alpha-d-ribofuranosyl-5,6-dimethylbenzimidazole;the benzimidazole nucleoside in vitamin B12. (05 Mar 2000) |
| alpha-santonin-1,2-reductase | <enzyme> From pseudomonas cichorii s.; catalyses the reduction of the 1,2-double bond of santonin; NADH or NADPH dependent Registry number: EC 1.3.1.- Synonym: santonin 1,2-reductase (26 Jun 1999) |
| alpha-sarcin | A fungal toxin that acts on the large subunit of rRNA and inactivates the ribosome. (05 Mar 2000) |
| alpha-streptococci | Streptococci that form a green variety of reduced haemoglobin in the area of the colony on a blood agar medium. (05 Mar 2000) |
| alpha substance | A filamentous plasmatic material, beaded with granules, demonstrable by means of vital staining in the immature red blood cells. Synonym: alpha substance, filar mass, filar substance, substantia reticularis, substantia reticulofilamentosa. Synonym: reticular formation. (05 Mar 2000) |
| Alpha tests | A set of paper and pencil-administered mental tests first used in the United States Army in 1917-1918 to determine the mental ability of literate recruits; the set includes 8 different types of tests: i.e., directions, arithmetical problems, practical judgement, synonyms and antonyms, disarrayed sentences, number series completions, analogies, and information; they are designed especially for testing large groups of individuals simultaneously, and for rapid machine scoring; distinguished from the Army Beta tests, a complementary set for administration to recruits who could not read or write English, in which the instructions are given in signs and the test material is pictorial. See: Beta tests. Synonym: Army Alpha tests. (05 Mar 2000) |