| 摘要 |
The light absorption spectrum of carbon isotopes 12CO2 and 13CO2 is measured highly accurately within a short period of time to determine a carbon isotopic abundance ratio highly accurately and reliably. Laser light emitted from a laser diode, which has been slightly modulated with a frequency f and swept in wavelength, passes through a specimen cell and is applied to a photodetector, which produces an electric signal converted from the detected laser light. 2f components of 12CO2 and 13CO2 of the light absorption spectrum are detected by a lock-in amplifier, and 3f components of 12CO2 and 13CO2 of the light absorption spectrum are detected by a lock-in amplifier. Spectral intensities of 12CO2 and 13CO2, which correspond to zero-cross points of the 3f components, are determined from peak values at three points of each of the 2f components, and a carbon isotopic abundance ratio of 12CO2 and 13CO2 is determined from a ratio of the spectral intensities.
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