National Geographic : 1958 Aug
Heart of the carbon laboratory: the counter tubes at the ends of the three lead-in pipes (three samples can be tested simultaneously in this multiple counter). They hide deep inside a cannonlike steel jacket filled with mercury and lead. Any cosmic ray that sneaks past this shield must penetrate the circle of Geiger counters (indicated by pencil). These turn off the main counters when extraneous radiation passes through. Tiny fingers of light flash on an electronic panel as carbon-14 atoms break down. Dials work like an electric meter, so the operator can read the total number of disintegrations at any time. Most laboratories run their tests at least 1,000 min utes; some continue two days. 245 Chemistry, Physics, and Electronics Combine Their Skills to Date Carbon Many visitors to a radiocarbon laboratory feel that they have stumbled onto a Rube Goldberg appa ratus. The technique calls for batteries of com plicated equipment. -Dating begins in the burning tube. There chunks of charcoal, bathed in a flow of oxygen, glow briskly at 2,000 ° F. Proper combustion leaves little ash. Carbon dioxide from the firing now courses through a tangle of pipes, flasks, and valves, where chemicals extract impurities (above). This Humble Oil & Refining Company geo chemist inspects a bank of tiny electric furnaces at Houston, Texas. Carbon dioxide is passing over heated metals-silver wire and copper chips-that remove oxides of nitrogen and sulphur and other contaminants. Substances vary widely in carbon content. It takes more bone than wood, for example, to pro duce the precise amount of gas needed for testing.