02 gennaio 2012

Infrared spectroscopy can detect trace gases for carbon dating


Paolo De Natale of the Italian National Research Council (CNR) and the European Laboratory for Non-Linear Spectroscopy (LENS), both in Florence, Italy, and his colleagues, unveiled a new high-sensitivity technique last year called saturated-absorption cavity ring-down spectroscopy (SCAR): Saturated-Absorption Cavity Ring-Down Spectroscopy (ref. Physical Review Letters, 104, 110801, March 2010. G. Giusfredi, S. Bartalini, S. Borri, P. Cancio, I. Galli, D. Mazzotti, P. De Natale; Istituto Nazionale di Ottica INO-CNR, and European Laboratory for Nonlinear Spectroscopy).
A new article, published 30 December 2011, explain the improved methd: Molecular Gas Sensing Below Parts Per Trillion: Radiocarbon-Dioxide Optical Detection (Phys. Rev. Lett. 107, 270802. I. Galli, S. Bartalini, S. Borri, P. Cancio, D. Mazzotti, P. De Natale, G. Giusfredi).
To determine the age of a sample, the SCAR technique uses a highly stable infrared laser to excite carbon dioxide molecules in a mirrored cavity. When the laser is turned off, trapped light dies away in the cavity (or “rings-down”) at a rate that depends on the amount of carbon-14 in the sample. The researchers stress the sensitivity of the system (that costs ten times less than an accelerator mass spectrometry) targeting rare carbon dioxide molecules containing carbon-14. This new optics-based method for detecting trace gases is based on infrared laser light to detect tiny amounts of carbon-14 in a gas sample. Then the system can detect a trace gas at a a lower pressure than any previous method has detected for a simple molecular gas (half of a femtobar: 10−15 times atmospheric pressure).
This system can help archelogy, but De Natale says that, in future, the technique could be adapted to detect tiny quantities of other rare molecules. This could allow it to be used to monitor the concentrations of hazardous pollutants in air and water, to detect explosives, and to conduct research in fundamental physics.

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