| 摘要 |
PROBLEM TO BE SOLVED: To accurately measure the light absorbing spectrum of<12> CO2 and<13> CO2 in a short period of time and obtain the existence ratio (isotope ratio) with high reliability for accuracy of stable carbon isotope. SOLUTION: A laser light emitted from a semiconductor laser 13 (LD) with a band of 2μm that is slightly modulated by frequency f and swept by wavelength is allowed to pass through an intake sample cell 2, and a photoelectric conversion signal is obtained by an optical detector 14. A 2f element of light absorbing element in the photoelectric conversion signal is detected by a lock-in amplifier 15, and a 3f element of light absorbing spectrum is also detected by a lock-in amplifier 16. Then, the intensity of 2f spectrum signal of<12> CO2 and<13> CO2 corresponding to zero-cross point of 3f element is obtained according to the peal values at upper and lower three points, and the ratio of carbon isotope is calculated according to the intensity ratio of obtained both spectrums.
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