Isotopes of argon
Argon (Ar) has 24 known isotopes, from 30Ar to 53Ar and 1 isomer (32mAr), three of which are stable, 36Ar, 38Ar, and 40Ar. On Earth, 40Ar makes up 99.6% of natural argon. The longest-lived radioactive isotopes are 39Ar with a half-life of 269 years, 42Ar with a half-life of 32.9 years, and 37Ar with a half-life of 35.04 days. All other isotopes have half-lives less than 2 hours, and most less than a minute. The least stable is 30Ar with a half-life shorter than 20 nanoseconds.
Naturally occurring 40K with a half-life of 1.248×109 (3) years, decays to stable 40Ar (10.72%) by electron capture and by positron emission, and also transforms to stable 40Ca (89.28%) via beta decay. These properties and ratios are used to determine the age of rocks through potassium-argon dating.
Despite trapping of 40Ar in many rocks, it can be released by melting, grinding, and diffusion. Almost all of the argon in the Earth's atmosphere is the product of potassium-40 decay, since 99.6% of Earth atmospheric argon is 40Ar, whereas in the Sun and presumably in primordial star-forming clouds, argon consists of < 15% 38Ar and mostly (85%) 36Ar. Similarly, the ratio of the three isotopes 36Ar: 38Ar: 40Ar in the atmospheres of the outer planets is measured to be 8400: 1600: 1
Argon
Argon is a chemical element with symbol Ar and atomic number 18. It is in group 18 of the periodic table and is a noble gas. Argon is the third most common gas in the Earth's atmosphere, at 0.934% (9,340 ppmv), making it over twice as abundant as the next most common atmospheric gas, water vapor (which averages about 4000 ppmv, but varies greatly), and 23 times as abundant as the next most common non-condensing atmospheric gas, carbon dioxide (400 ppmv), and more than 500 times as abundant as the next most common noble gas, neon (18 ppmv).
Nearly all of this argon is radiogenic argon-40 derived from the decay of potassium-40 in the Earth's crust. In the universe, argon-36 is by far the most common argon isotope, being the preferred argon isotope produced by stellar nucleosynthesis in supernovas. In addition, argon is the most prevalent of the noble gases in Earth's crust, with the element composing 0.00015% of this crust.
The name "argon" is derived from the Greek word αργον, neuter singular form of αργος meaning "lazy" or "inactive", as a reference to the fact that the element undergoes almost no chemical reactions. The complete octet (eight electrons) in the outer atomic shell makes argon stable and resistant to bonding with other elements. Its triple point temperature of 83.8058 K is a defining fixed point in the International Temperature Scale of 1990.
KH-5 Argon
KH-5 ARGON was a series of reconnaissance satellites produced by the United States from February 1961 to August 1964. The KH-5 operated similarly to the Corona series of satellites, as it ejected a canister of photographic film. At least 12 missions were attempted, but at least 7 resulted in failure. The satellite was manufactured by Lockheed. Launches used Thor-Agena rockets flying from Vandenberg Air Force Base, with the payload being integrated into the Agena.
Payload
Different versions of the satellite varied in mass from 1150 kilograms to 1500 kg. At least two missions deployed ELINT subsatellites. Ground resolution for the satellite was 140 meters, with a swath of 556 km. The onboard camera had a focal length of 76 mm. The purpose of the system, which produced relatively low-resolution images compared to other spy satellites, was to provide imagery for mapmaking purposes. This was one of the tasks that had originally been planned for the Samos series of satellites equipped with the (quickly cancelled) "E-4" cameras. Each satellite took photographs for less than a week before returning its film.
Argon (1908 automobile)
The Argon was made by Grannaway Engineering Co, Earls Court, London S.W. in 1908. It was a fairly large touring car using a 25 hp 6-cylinder Coventry-Simplex engine. It was priced at 750 pounds. In 1905, the company was said to be planning a car deemed the Grannaway, but it is not clear whether this ever came to fruition.
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