Photoacoustic optical frequency comb spectroscopy of radioactive methane in the mid-infrared region

Abstract

The standard method for sensitive measurements of long-lived radioactive isotopes, such as 14C, is accelerator mass spectrometry (AMS). The AMS facilities are indispensable for applications like radiocarbon dating, but too expensive and massive for in-situ measurements. Laser spectroscopy, on the other hand, is a promising solution for isotope-selective detection of gas-phase compounds in applications that require low-cost instrumentation and on-site measurement capability. The recent work on laser spectroscopy of 14CO2 has led to impressive detection limits below the natural 14C abundance [1,2], which encourages us to develop similar techniques also for other radiocarbon compounds. Here, we report the first spectroscopic study of radioactive methane, 14CH4. Our work is motivated by a number of important applications, such as determining the biofraction of methane fuel mixtures and in-situ monitoring of radioactive gas emissions at decommissioning sites of light water nuclear reactors. © 2019 IEEE.