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R. Massée H. A. Van Der Sloot H. A. Das 《Journal of Radioanalytical and Nuclear Chemistry》1977,35(1):157-165
A method for the determination of selenium by preconcentration and thermal neutron activation is presented. Selenium is adsorbed
on active charcoal after reduction to the elemental state. By varying the conditions of the reduction, it is possible to measure
the total selenium content and tetravalent selenium separately. The contribution of hexavalent selenium is obtained by substraction.
The lower limit of determination is 5 ng°1−1. About 40 samples per day can be handled by one analyst. The preconcentration can be performed at the sampling site resulting
in samples, which can be stored easily for later analyses by neutron activation. 相似文献
909.
The infrared emission of CO trapped in solid Ne and Ar is observed at low temperature. The first vibrational level of 12C16O is excited by a Q-switched frequency doubled CO2 laser. The emission spectrum consists of several lines arising from upper vibrational levels of 12C16O and also of 13C16O and 12C18O which are present in natural abundance. An interpretation is proposed which is based on the assumption that long range dipole—dipole interaction is the main physical process involved in these experiments. Resonance energy transfer produces an energy migration among 12C16O molecules without any change in vibrational populations. Phonon assisted energy transfer takes place between vibrational levels of the various isotopic species present in the solution. In order to satisfy the resonance condition a phonon is emitted or absorbed whose energy compensates for the energy mismatch between the transitions in each interacting molecule due to isotopic effect and or vibrational anharmonicity. The range of this process is greatly extended by energy migration. At the low phonon bath temperature phonon emission is much more probable than phonon absorption. So a strong excitation of upper vibrational levels with in some cases population inversions is observed.Molecular impurities act as efficient quenching centers even at very low concentration. When highly purified samples are used, the fluorescence decay time is found to be 20.6 ms in Ne and 14.5 ms in Ar and does not significantly depend upon concentration and temperature. It is concluded that radiationless relaxation is unimportant. 相似文献
910.
Gans und Goldschmidt Elektrizitäts-Ges. m. b. H. Berlin W. A. Roth J. Shukow A. Gerassimov Tödt Rossée v Morgenstern E. E. Weibel A. L. Thuras H. T. Stern F. Scheminzky R. Lorenz H. Klauer R. E. Hall L. H. Adams und O. Pfundt 《Fresenius' Journal of Analytical Chemistry》1928,75(3-4):120-123
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