S. Le Caër

Solid-state NMR characterization of a controlled-pore glass and of the effects of electron irradiation.

Controlled-pore glasses (CPGs) are silica-based materials which provide an adequate model system for a better understanding of the radiation chemistry of glasses, especially under nanoscopic confinement. This paper presents a characterization of a nanoporous CPG before and after electron irradiation using multinuclear solid-state magnetic resonance (NMR). 1H MAS NMR has been used for studying the surface proton sites and it is observed that the irradiation leads to a dehydration of the material. Accordingly, concerning the silicon sites near the surface, the observed variation of the Q4, Q3 and Q2 species from 1H-29Si CPMAS spectra shows an increase of the surface polymerization under irradiation, implying in majority a Q2 to Q3/Q4 conversion mechanism. Similarly, 1H-17 O CPMAS measurements exhibit an increase of Si-O-Si groups at the expenses of Si-OH groups. In addition, modifications of the environment of the residual boron atoms are also put in evidence from 11B MAS and MQMAS NMR These data show that MAS NMR methods provide sensitive tools for the characterization of these porous glasses and of the tiny modifications occurring under electron irradiation.

Experimental and theoretical study of the degradation of malonamide extractant molecules under ionizing radiation

The behavior of three malonamides diluted in octane and submitted to ionizing radiation has been studied by means of in situ infrared spectroscopy, electrospray ionization mass spectrometry and quantum chemistry calculations. The major channel at low dose for a malonamide with ethyl groups on the nitrogen atoms and no substituent on the central carbon atom arises from the addition of an octyl group from the solvent. Adding alkyl chains on the nitrogen atoms and/or an alkyl chain on the central carbon atom weakens the central C–C bond which is then preferentially cleaved upon irradiation. The other bond cleavages (both C–N and C–H cleavages) are then detected when increasing the dose.