Saturated-absorption CAvity Ring-down (SCAR) spectroscopy has already demonstrated to achieve the highest Noise-Equivalent-Concentration (NEC) sensitivity (a few parts-per-quadrillion, ppq), among all molecular spectroscopy techniques, on radiocarbon dioxide (14CO2). [1-6] This is very important for the applications, considering the ubiquitous role of carbon dioxide and the key role of its unstable isotope, 14CO2, as a sensitive marker of bio vs. fossil materials. Indeed, the ~5.7 kyears half life of 14C progressively transmuting in nitrogen by beta emission, represents a natural clock that can be used to distinguish young materials, recently (as compared to 14C half life) produced by the biosphere, and thus in equilibrium with the radiocarbon concentration there, and old materials, like fossil-fuels based ones. Therefore, SCAR proved to be a powerful tool to precisely measure the ratio of bio vs. fossil fraction in fuels, below the natural abundance in the biosphere, that is about 1 part-per trillion (ppt). [4] Moreover, its superior dynamic range (as compared to Accelerator Mass Spectrometry-AMS) could be used to discriminate between materials with different levels of exposure to irradiation, in nuclear installations, in samples enriched (with respect to the natural abundance) more than 30 times in 14C. [5] Recently, the intrinsic nonlinear nature of the SCAR technique, first described in 2010 [1], was exploited for high precision frequency measurements of cold molecular acetylene transitions. [6] Archaeological applications can be very challenging, even at the sensitivity levels of SCAR, when the remains to analyze are very old, thus with a low residual concentration of 14C. Some results, on samples from a 4,500-year-old Sumerian site, will be shown. [7] We are now testing new ultra-compact SCAR configurations, for biomedical applications, as well as purification methods of carbon dioxide from atmospheric samples. This latter methodology should make possible the application of SCAR to one of the hottest world-scale issues, climate change monitoring, by real-time measurement of the 14C/12C in carbon dioxide. Such a demonstration could be followed by the deployment of SCAR instrumentation worldwide.
Literature:
[1] Galli I., Phys. Rev. Lett. 2010, 104, 110801. [2] Galli I., Phys. Rev. Lett. 2011, 107, 270802. [3] Galli I., Optica 2016, 3, 385. [4] Delli Santi M. G., Adv. Photon. Res. 2021, 2, 202000069. [5] Delli Santi M. G., Proc. Natl. Acad. Sci. USA 2022, 119, e2122122119. [6] Aiello, R., Nat. Commun. 2022, 13, 7016. [7] Delli Santi M. G., manuscript in preparation
