A recommendation letter or letter of recommendation, also known as a letter of reference, reference letter or simply reference, is a document in which the writer assesses the qualities, characteristics, and capabilities of the person being recommended in terms of that individual's ability to perform a particular task or function.
This article is about stable isotope ratios. For the general category of stable nuclides, see Stable nuclide. The term stable isotope has a similar meaning to stable nuclide, but is preferably used when speaking of nuclides of a specific element.his article is about stable isotope ratios. For the general category of stable nuclides, see Stable nuclide. The term stable isotope has a similar meaning to stable nuclide, but is preferably used when speaking of nuclides of a specific element.
The stable form of carbon is carbon 12 and the radioactive isotope carbon 14 decays over time into carbon 12 and other particles. Carbon is naturally in all living organisms and is replenished in the tissues by eating other organisms or by breathing air that contains carbon.At any particular time all living organisms have approximately the same ratio of carbon 12 to carbon 14 in their tissues.he stable form of carbon is carbon 12 and the radioactive isotope carbon 14 decays over time into carbon 12 and other particles. Carbon is naturally in all living organisms and is replenished in the tissues by eating other organisms or by breathing air that contains carbon.