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Abstract  

The phase diagram of R(+)-S(-) efaroxan hydrochloride (Tfus.(R)=245.10.3C. ΔHfus.(R)=119.63.0 J g-1) shows a racemic compound. The melting temperature and melting enthalpy of the compound are: Tfus.(RS)=247.80.2C and ΔHfus. (RS)=124.62.4 J g-1. A solid ↔ solid transformation takes place at Ttrs.=1801C, ΔHtrs.=15.00.4 J g-1. This transition is observed between 3 and 97% R(+). The stability of the racemic compound already established in a previous study was confirmed by the value of Petterson's coefficient (i=1.19). The two eutectic positions at 20 and 80% R(+) that define the range over which the racemic compound is found, exclude the use of resolution methods by preferential crystallization.

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Abstract  

The physicochemical characterization of the solid-state enantiomers and racemate of efaroxan hydrochloride (C13H17N2O+Cl-, M=252.5 g mol-1) was performed by thermoanalytical methods (differential scanning calorimetry, thermogravimetry and thermomicroscopy) and spectral methods (infrared spectrometry and X-ray diffractometry). The efaroxan enantiomers and racemate were shown to be unstable near the melting point. At the beginning of the decomposition, a loss of hydrogen chloride was observed. However when sealed pans were used, the compounds decomposed at higher temperature, allowing a precise evaluation of the melting enthalpies by means of differential scanning calorimetry. The nature of the racemate and its thermal stability were assessed by evaluating its free formation enthalpy. An enantiotropic solid-solid transformation (II→I) was noted for the racemate; the reverse process (I→II) follows zero-order kinetics.

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Abstract  

The amplitude-energy relationships for surface barrier detectors were measured for4He and12C particles, as well as the corresponding energy resolutions. It is shown that the use of12C beams presents no marked advantage for increasing mass or depth resolution. On the other hand pile-up phenomena are drastically reduced by using12C backscattering. Applications are shown to the determination of trace amounts of Sb or Yb near the surface of iron. Gold contaminations of silicon surfaces were precisely measured within minutes down to 5·1011 gold atom/cm2, the limiting sensitivity being of the order of 1010 atom/cm2 for traces of heavy elements, such as Au, Hg, Pb, etc. Sensitivities for lighter elements are discussed.

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Journal of Radioanalytical and Nuclear Chemistry
Authors: G. Amsel, B. Agius, D. Dieumegard, B. Maurel, J. Nadai, C. Ortega, S. Rigo, J. Siejka, M. Croset, and G. Velasco
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Journal of Radioanalytical and Nuclear Chemistry
Authors: F. Abel, G. Amsel, E. d'Artemare, M. Bruneaux, C. Cohen, B. Maurel, C. Ortega, S. Rigo, J. Siejka, M. Croset, and D. Dieumegard

Abstract  

Techniques are described which combine the use of nuclear reactions and of backscattering to obtain analytical results which would be difficult or impossible to reach using one of these methods only. The principles of stoichiometry determination by plateau height analysis are developed both for backscattering and for narrow resonances of nuclear reactions. Examples of applications are given to the determination of the composition of various thin films of aluminium and silicon oxides, silicon nitrides and calcium fluorides. The analysis of samples smaller than the beam, using backscattered particle monitoring, is presented.

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