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Physical methods make it possible to combine analytical imaging with isotopic labelling in biological studies. With radioactive isotopes, track- radioautography may be used (in parallel with conventional grain-density radioautography) for high lateral resolution, even with energetic β-rays; in macroradioautography, filmless methods (gaseous detectors, scintillation counters, and storage phosphor screen devices) have remarkable performances. Neutron capture radiography is used mainly for the detection and imaging of one stable isotope of a few elements which have no radioisotope of practical use. With nuclear microprobes, nuclear reaction analysis and scattering analysis may serve to discriminate between isotopes (including stable isotopes). Secondary ion mass spectrometry images any isotope of almost any element with very good detection limits and a resolution better (sometimes much better) than 1 μm. Preventing the diffusion of mobile substances during the preparation of the biological specimens is still...

Oxygen deficient YBa 2 Cu 3 O x thin films, in-situ deposited by laser ablation on (100) SrTiO 3 substrates have been treated ex-situ under diluted NF 3 flow at 280°C. After a short time of treatment, a clear improvement of the superconducting behaviour, i.e. an increase of Tc and a decrease of the inductive transition width are observed. Comparisons are made between reactions under NF 3 and under O 2 or N 2 in the same conditions of reactions, leading to the conclusion that in all cases the NF 3 treatment is the best to improve the superconducting behaviour of these thin films. The kinetics of the NF 3 reaction with these films is compared to the one previously observed for oxygen deficient thin films deposited by laser ablation on (100) MgO.