Etymology
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roentgen 

in physics, 1896, in Roentgen rays "X-rays," in recognition of German physicist Wilhem Conrad Röntgen (1845-1923), who discovered X-rays in 1895. As a unit of exposure to radiation, it is attested from 1922, proposed in French in 1921.

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radiography (n.)

1896, "science or process of making images of objects on a sensitive plate by means of x-rays," from radiograph, the word for such an image-making device; from radio-, combining form of radiation, + -graph. Radiograph was used earlier as "device to measure and record the intensity of sunshine" (1880).

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pulsar (n.)

"highly magnetized, rotating compact star that emits beams of electromagnetic radiation," 1968, from pulse (n.1), the form on analogy of quasar. When discovered in 1967 via radio telescope, they were thought perhaps to be signals from alien civilizations and astronomers informally dubbed them LGM for "Little Green Men."

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irradiate (v.)
c. 1600, "to cast beams of light upon," from Latin irradiatus, past participle of irradiare "shine forth, beam upon, illumine," from assimilated form of in- "into, in" (from PIE root *en "in") + radiare "to shine" (see radiate (v.)). Meaning "expose to radiation other than light" (originally X-rays) is from 1901. Related: Irradiated; irradiating.
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dew (n.)

"water vapor deposited from the atmosphere by condensation, especially during the night," Middle English deaw, deu, from Old English deaw, from Proto-Germanic *dawwaz (source also of Old Saxon dau, Old Frisian daw, Middle Dutch dau, Old High German tau, German Tau, Old Norse dögg "dew"), perhaps from PIE root *dheu- "to flow" (source also of Sanskrit dhavate "flows, runs").

Used figuratively of something refreshing (late Old English), or suggestive of morning and youthful freshness (1530s). As a verb, "to wet with or as with dew," Old English deawian.

The formation of dew is explained by the loss of heat by bodies on the earth's surface through radiation at night, by which means they and the air immediately about them are cooled below the dew-point ....Dew is thus deposited chiefly on bodies which are good radiators and poor conductors of heat, like grass; hence also it appears chiefly on calm and clear nights--that is, when the conditions are most favorable for radiation. It never appears on nights both cloudy and windy. In winter dew becomes hoar frost. [Century Dictionary]
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gamma 
third letter of the Greek alphabet, c. 1400, from Greek gamma, from Phoenician gimel, said to mean literally "camel" (see camel) and to be so called for a fancied resemblance of its shape to some part of a camel. Gamma rays (1903) originally were thought to be a third type of radiation, but later were found to be very short X-rays.
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beta (n.)

second letter of the Greek alphabet, c. 1300, from Greek, from Hebrew/Phoenician beth (see alphabet); used to designate the second of many things. Beta radiation is from 1899 (Rutherford). Beta particle is attested from 1904. Beta male, pejorative term for a risk-avoidant, non-confrontational man perceived as a follower or supporter rather than a leader, is by 2005, transferred from zoology (birds, primates), where it is attested by 1962 (compare alpha male under alpha).

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emanation (n.)

"act of flowing or issuing from an origin; emission; radiation; what issues, flows, or is given out from any substance or body;" 1560s, from Late Latin emanationem (nominative emanatio), noun of action from past-participle stem of Latin emanare "flow out, spring out of," figuratively "arise, proceed from," from assimilated form of ex "out" (see ex-) + manare "to flow," from PIE root *ma- (3) "damp."

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laser (n.)
1960, acronym for "light amplification by stimulated emission of radiation," on pattern of maser (1955). A corresponding verb, lase, was coined by 1962. Related: Lasered; lasering. Laser disc recorded from 1980. Earlier laser was the name of a type of gum-resin from North Africa used medicinally (1570s), from Latin; still earlier it was an Old English and Middle English name for some weed, probably cockle.
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beam (n.)

Old English beam originally "living tree," but by late 10c. also "rafter, post, ship's timber," from Proto-Germanic *baumaz "tree" (source also of Old Frisian bam "tree, gallows, beam," Middle Dutch boom, Old High German boum, German Baum "tree," and perhaps also (with unexplained sound changes) Old Norse baðmr, Gothic bagms), which is of uncertain etymology (according to Boutkan probably a substrate word). The shift from *-au- to -ea- is regular in Old English.

Meaning "ray of light" developed in Old English, probably because beam was used by Bede to render Latin columna (lucis), the Biblical "pillar of fire." Meaning "directed flow of radiation" is from 1906. To be on the beam "going in the right direction" (1941) originally was an aviator's term for "to follow the course indicated by a radio beam." Nautical sense of "one of the horizontal transverse timbers holding a ship together" is from early 13c., hence "greatest breadth of a ship," and slang broad in the beam, by 1894 of ships, of persons, "wide-hipped," by 1938.

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