See also: Carbon-14 (homonymy)
Its single mode of disintegration is done by emission of a Particule beta of 156 keV while being transmuted into nitrogen NR; with a radioactive Half-life 5730 years (± 40 years). Carbon-14 was a long time the only radioisotope of carbon to have applications. For this reason, it was called radiocarbon .
biological Carbon dating
The carbon-14 was discovered on February 27th, 1940 by Martin Kamen of the Radiation Laboratory and Samuel Ruben of the department of Chemistry of the the University of California, Berkeley.
As of 1934, in Yale, Franz Kurie suggests the existence of carbon-14. It observes indeed sometimes that the exposure of Azote to Neutron S rapids produces in a cloud chamber of Wilson a long fine trace instead of the short thicker trace left by a particle alpha. As of 1936, it is established that the fast neutrons react with nitrogen to give Bore while the slow neutrons react with nitrogen to form carbon-14. This corresponds to “discovered to the physical direction” of carbon-14 in opposition to its “discovery to the chemical direction”, i.e. its production in sufficient quantity to be able to measure a Activité.
Kamen and Ruben collaborate in interdisciplinary research on the biological tracer with an aim of determining the initial product of the fixing of carbon dioxide during photosynthesis. The use of the Carbone 11 as tracer is very difficult because of its radioactive short period (21 minutes). Ruben however tries to develop a technique of study of photosynthesis: it makes push a plant in the presence of carbon dioxide containing of carbon 11, kills it, then separates and analyzes its chemical components, before the radioactivity does not become undetectable, to find which components contain the tracer. The failure of this technique stimulates the search for another radioactive isotope at more radioactive long period, carbon-14.
One of the independent sources of financing of Radiation Laboratory is manufacture in its Cyclotron S of radioisotopes for biomedical research. With the end of the year 1939, Ernest Orlando Lawrence, director of Radiation Laboratory, is anxious competition of rare stable isotopes like carbon 13, nitrogen 15 or oxygenates it 18 which can replace radioisotopes like biological tracers. It offers to Kamen and Ruben an access unlimited to the cyclotrons of 37 and 60 inches to seek radioisotopes of higher radioactive half-lives for the principal elements present in the organic compounds: hydrogen, carbon, nitrogenize or oxygenate.
This systematic research campaign starts with carbon. Kamen and Ruben bombard graphite with deutons (cores of Deutérium). The weak activity that they measure on February 27th, 1940, of approximately four times the background noise, confirms the existence of carbon-14 with one radioactive half-life which appears quite higher (several thousands of years) than what the theory envisaged. This high radioactive half-life, and thus the weak activity of the carbon-14, explains why this one was not before discovered.
Kamen and Ruben note thereafter that the reaction of slow neutrons with nitrogen to give carbon-14 is definitely more productive than the reaction deuton-carbon 13 .
The application of carbon-14 as tracer biological remainder however limited by its production costs, the cyclotron being the only neutron source available.
After the Second world war, the development of the nuclear reactors, which use graphite like regulator, the massive production of carbon-14 authorizes, whose employment is spread in all the fields of biomedical research.
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