Use of micro-Raman spectrometry coupled with scanning electron microscopy to determine the chemical form of uranium compounds in micrometer-size particles

In the frame of nuclear safeguards, knowledge of the chemical form (stoichiometry) of the uranium compounds present in the micrometric particulate material sampled by wiping surfaces in an inspected nuclear facility may point out the industrial process implemented in the installation. Micro-Raman spectroscopy (MRS) coupled with scanning electron microscopy (SEM) has been used for the first time to analyze micrometer-size particles of various uranium oxides [UO2, U3O8, UO3, and UO4 · 4(H2O)] deposited on carbon disks. Uranium particles are detected by means of SEM, and Raman analysis is then directly carried out inside the SEM measurement chamber without moving the carbon disk from SEM to MRS. When particles are deposited on appropriate carbon disks (sticky carbon tapes), despite a loss of signal-to-noise ratio of about an order of magnitude with regard to the stand-alone MRS, all uranium oxides are successfully identified in particles by in-SEM Raman analysis, obtaining similar characteristic bands as the ones obtained with the stand-alone MRS. Moreover, with the SEM–MRS coupling, particles as small as 1 µm can be analyzed, whereas, without the SEM–MRS coupling, only particles larger than ~5 µm are efficiently analyzed, after localization inside the SEM, transfer of the sample holder into the MRS, and relocation of the particles inside the MRS. Copyright © 2013 John Wiley & Sons, Ltd.