Estimation of sensitivity of the IR spectroscopic method to detect water vapor radioactive isotopologues content

There are different sources of the H₂O radioactive isotopologues on the Earth.  They can arise under the cosmic rays exposure and lightning discharge, and then it penetrates with precipitation into the hydrologic system and soil. The man-caused sources of the H₂O radioactive isotopologues are more significant. Much quantity of tritium isotopologues HTO and T₂O are emitted during nuclear power station accidents and nuclear explosions.  For example, about 0.2-0.1 PBq of tritium fell into the environment [1]. The radioactive water as well as its evaporation is dangerous for all living beings, and therefore the monitoring of the H₂O radioactive isotopologues content in the water and air is very important.

   
    The most long-lived oxygen radioactive  isotopologues of water vapor are Н₂¹⁴О, Н₂¹⁵О and Н₂¹⁹О. The most long-lived hydrogen radioactive  isotopologues are the tritium  isotopologues HTO and T₂O (half-value period of tritium is 12.32 years). Therefore, they are the most perspective among the H₂O radioactive isotopologues for the IR spectra registration and their concentration detection. At present, there is a little quantity of measured absorption spectra of the H2O radioactive isotopologues, and our theoretical calculations of the absorption spectra can help to detect these substances in the radioactive water evaporation. In contrast to currently available methods based on sampling and beta-radiation detection, the IR spectroscopy can measure trace levels of the isotopologues non-invasively and in real time.

    In the work, the sensitivity of the IR spectroscopy method to measurement of the H₂¹⁹O, H₂¹⁵O, H₂¹⁴O, НТО and T₂O content in the radioactive water evaporation is investigated.   On basis of our new theoretical calculations of the H₂¹⁹O, H₂¹⁵O and H₂¹⁴O absorption line parameters [2-4] and calculation of the HTO and T₂O [5], the simulation of transmission spectra  was carried out at large variation of the isotopologues concentrations.  The most perspective spectral intervals for these isotopologues detection in water vapor are found with taking into account of the absorption lines overlapping. Threshold values of their concentrations which can be defined from the IR absorption spectra measurements in the laboratory and atmospheric conditions are estimated. It is shown that the  HT₁₆O and T₂¹⁶O can be detected in the tritium water vapor when their concentration is 0.01-0.05% relative to the H₂¹⁶O content. The H₂¹⁹O, H₂¹⁵O, H₂¹⁴O isotopologues  imprints are distinctly observed in the radioactive water vapor spectra at their concentrations more than 0.1% relative to the H₂¹⁶O content.

The research was supported by the Ministry of Science and Higher Education of the Russian Federation ( IAO  SB RAS).

1. K. Kheamsiri, D. Anderson, H. Tazoe, et al. Elevated levels of tritium in surface water collected in the immediate aftermath of the Fukushima accident // Environmental Pollution. 2025. P. 126040

 
2. Voronin B. A., Tennyson J., Yurchenko S. N., Chesnokova T. Yu., Chentsov A.V., Bykov A. D., Makarova M. V., 3. Voronina S. S., Cruz F. C.// Spectrochimica Acta Part A: Molec. and Biomolec. Spectrosc. V. 311. 2024. N.124007, P.1-12. 

3. B.A. Voronin, J. Tennyson, T.Yu. Chesnokova, A.V. Chentsov, A.D. Bykov  // Mol. Phys. 2024. V.122. N5.  

4. B.A. Voronin, J. Tennyson, T. Yu. Chesnokova, A. V. Chentsov, A.D Bykov // J. of Radioanalytical and Nuclear Chemistry. 2024.  V. 333. P. 4945–4954

5. https://spectra.iao.ru/molecules