Isotope analysis by infrared laser absorption spectroscopy

Abstract

The feasibility of IR laser spectroscopy as a technique for the measurement of small abundances of stable and radioactive isotopes has been examined. Theoretical considerations and first experimental results with two laser systems are presented: 1) Coincidences between emission lines of a CO2-laser and absorption lines of13C-substituted ethylene can be used to determine the13C-concentration of C2H4. 2) A tunable PbS-diode laser emitting in the 4.3 μm-spectral region of the rotation-vibration bands of CO2 can be used to determine abundances of12C,13C,16O,17O and18O in small samples of CO2. With optimized performance, sensitivities up to 10−9–10−10 seem possible, and for higher abundances an accuracy of 10−3. This should allow geophysical isotope studies to be performed and it is hoped that the technique will eventually be applicable to measuring the activity of long-lived radioisotopes.