Average cross-sections for (n, α) and (n,p) reactions on titanium in a fission-type reactor spectrum

The average cross-section in a fission-type reactor spectrum was determined experimentally for the reactions:⁴⁶Ti(n,p)⁴⁶Sc,⁴⁷Ti(n,p)⁴⁷Sc,⁴⁸Ti(n,p)⁴⁸Ti(n,α)⁴⁵Ca and⁵⁰Ti(n,α)⁴⁷Ca. In order to obtain the (n,p) cross-sections, reactor irradiation of titanium was followed by measurement of the induced scandium activities with a Ge(Li) detector of calibrated detection efficiency. For this no chemical separations had to be carried out. For the (n,α) reactions, however, the induced calcium activities were separeted and purified by oxalate precipitation, after the bulk of the radioactivity had been removed by precipitation of titanium hydroxide. The⁴⁷Ca disintegration rate was determined in the same way as for the scandium isotopes, whereas for⁴⁵Ca liquid scintillation counting was carried out. The shape of the reactor spectrum was investigated by irradiating reference threshold detectors with different effective threshold energies. To correct for (n,γ) interferences, irradiations were carried out with and without cadmium shielding. On the basis of \(\bar \sigma _F = 0.64\) mb for the reaction²⁷Al(n,α)²⁴Na, the average cross-sections were as follows:⁴⁶Ti(n,p)⁴⁶Sc:10.5±0.4 mb;⁴⁷Ti(n,p)⁴⁷Sc: 16.3±0.6 mb;⁴⁸Ti(n,p)⁴⁸Sc:0.272±0.005 mb;⁴⁸Ti(n,α)⁴⁵Ca: 34μb;⁵⁰Ti(n,α)⁴⁷Ca: 8.1±0.3 μb.     

Finitude du nombre des classes d'isomorphisme des structures isometriques entières

Sans résumé Cet article contient l'essentiel de la thèse des auteurs soutenue à l'Université de Genève.     

Total cross section for neutrino charged current interactions at 3 GeV and 9 GeV

Average total cross sections are given for neutrino charged current interactions at neutrino energies of 2.87 GeV and 9.05 GeV. The ratios $\text{〈σ〉}\text{〈E〉}\text{are}\text{0.69 ± 0.05}\text{and}\text{0.61 ± 0.06}$ in units of 10^?38 cm²/GeV nucleon, respectively The errors include both statistical and systematic uncertainties.     

K-flots et théorème de renouvellement

It is shown that for certain dynamical systems (among them Bernoulli systems, some Markov chains and quasi-Bernoulli systems), and for a certain class of functions, either the flow built under the function is K, or the set of values of the function is arithmetical. From that result one deduces a generalization of the classical renewal theorem, with a necessary and sufficient condition.     

Probing ionic association on metal oxide clusters by pulsed field gradient NMR spectroscopy: the example of Sn12-oxo clusters

Pulsed field gradient (1)H NMR spectroscopy has been applied to investigate the association behavior of the Sn(12)-oxo cluster macrocation [(BuSn)(12)O(14)(OH)(6)](2+) with two different and smaller anions, p-toluenesulfonate (PTS(-)) and diphenylphosphinate (Ph(2)PO(2) (-)). By monitoring the translational diffusion coefficients of the various species involved, it is shown that the association depends on the anion involved and on the solvent used. Moreover, the possibility to individually monitor the diffusion characteristics of multiple anionic and cationic species in mixtures, by virtue of resolved (1)H resonances available from each species, allows us to evidence the occurrence of ion exchange in such systems. Thus when [(BuSn)(12)O(14)(OH)(6)](PTS)(2) is mixed with two equivalents of Ph(2)PO(2)NMe(4), PTS(-) is displaced by Ph(2)PO(2) (-), highlighting the greater affinity of the organotin macrocation for the diphenylphosphinate. This example clearly illustrates the potential of pulsed field gradient (1)H NMR spectroscopy in inorganic/organometallic chemistry, to follow preferential ion pairing in multi-ion systems at the level of each individually charged species.