Isotopic analysis of carbon, nitrogen and oxygen by nuclear reactions

A description is given of two processes for simple determination, without preliminary chemical preparation, of the 13C/12C, 15N/14N, 15N/12C or 18O/16O isotopic concentration ratios in biological samples or in other materials. The carbon and nitrogen analyses are carried out by direct observation of the nuclear reactions 12C(p,γ)13N, 14N(p,γ)15O, 13C(p,γ)14N and 15N(p,αγ)12C, induced by low-energy protons. The determination of 12C by delayed measurement of the positrons emitted by nitrogen-13, which is particularly useful in certain cases, is taken into consideration. In the case of oxygen, the method is based on induction of the photo-nuclear reactions 16O(γ,n)15O and 18O(γ,p)17N. The activities from oxygen-15 and nitrogen-17, which emit positrons and delayed neutrons respectively, are measured with a device which can automatically analyse about 120 samples in two hours. The possibilities of the methods presented, some of which appear very useful for the systematic analysis of large series of solid or liquid samples, are discussed. (author)