Isotope analysis by infrared laser absorption spectroscopy

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.