Gas measuring apparatus

Abstract

A gas measuring apparatus includes a cell portion, a light source portion, a detection portion, and a control portion. The cell portion includes a space into which a sample gas containing breath containing a first isotope of carbon dioxide and a second isotope of carbon dioxide is introduced. The light source portion changes a wavelength of the light in a band of 4.345 μm or more and 4.384 μm or less. The detection portion performs an operation including first detection of an intensity of the light passing through the space and second detection of an intensity of the light passing through the space into which the sample gas is not introduced. The control portion calculates a ratio of an amount of the second isotope to an amount of the first isotope based on a result of the first detection and a result of the second detection.

What is claimed is: 
     
         1 . A method for measuring a sampling gas containing a first isotope of carbon dioxide and a second isotope of carbon dioxide, comprising:
 emitting a light operable to sweep a wavenumber within a range of 1 cm −1  toward the sampling gas, the range including a first wavenumber corresponding to one of absorption peak of the first isotope, a second wavenumber corresponding to one of absorption peak of the second isotope and a third wavenumber corresponding to absorption peak of the first isotope or the second isotope, absorption of the first isotope at the second wavenumber not corresponding to absorption peak and being lower than absorption of the second isotope, the wavenumber being not less than 2281 cm −1  and not more than 2301 cm −1 ;   measuring a first intensity of the light passing through the sampling gas within the range; and   calculating a ratio of an amount of the second isotope to an amount of the first isotope based on the first intensity.   
     
     
         2 . The method according to  claim 1 , wherein a semiconductor light-emitting element emits the light by energy relaxation of electrons in subbands in a plurality of quantum wells. 
     
     
         3 . The method according to  claim 1 , wherein
 the measuring further includes measuring a second intensity of the light passing through a reference gas within the range, and   the calculating is performed based on the first intensity and the second intensity.   
     
     
         4 . The method according to  claim 1 , wherein the ratio is calculated a plurality of times. 
     
     
         5 . The method according to  claim 3 , wherein the ratio is calculated a plurality of times. 
     
     
         6 . The method according to  claim 1 , wherein
 the first isotope is  12 CO 2 , and   the second isotope is  13 CO 2 .