Abstract : Radiations from 11C and 18p produced in the 3He activation of carbon and oxygen were used to detect the presence of these elements. Using targets of known composition, the cross-sections for the 3He + C → 11C and 3He + O → 18F reactions were measured as a function of energy up to 5.5 MeV. The results show that the cross sections for both reactions are of the order of tens of mb at a 3He laboratory energy as low as 2 MeV. This corresponds to a sensitivity of the order of ppm for the carbon and oxygen analyses. The 3He + N → 13N reaction, which can serve as the detecting reaction for nitrogen, was found to have much lower cross-sections (1).
