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On décrit la détermination de traces dans le germanium, le silicium et le sélénium. En appliquant des techniques gamma spectrométriques, précédées ou non de séparations chimiques il est possible de doser les éléments suivants dans (1) germanium: As, Cu, Au, Ga, Zn, Hg, Cr, Sn, Sb, Co, In, Ni, Ir, Se, Sc, Ag, Ta, Hf et U; (2) silicium: P, Au, Sb, Ga, Fe, K, Cr, Mo, Sn, As, Co, In, Zn, Cu, W, Ta, Na, Eu, Sm, La, Sc et T1; (3) sélénium: Cl, Br, I, P, S, Te, Na, K, Cr, Fe, Co, Cu, Zn, Ga, Sc, Ag, Cd, La, W, Au et Tl. Les concentrations et ou limites de détections varient de quelques parties par million à 10−3 parties par milliard.
The determination of oxygen in lead by3He and4He activation analysis was studied. Both methods were applied to the same material containing 0.9 μg·g−1 of oxygen. The18F formed from oxygen was separated from matrix activities by extraction of Po with N-benzoyl-N-fenylhydroxylamine, followed by distillation of fluorosilicic acid and precipitation of lead fluorochloride (4He activation) or by distillation followed by precipitation (3He activation). The yield of the separation, which amounted on the average to 68%, was determined via the19F(n,4He)16N reaction. The coefficients of variation were 21 and 45% for4He and3He activation analysis, respectively, thus indicating a less homogeneous distribution of the oxygen. Nuclear interferences of sodium and fluorine were shown to be negligible.
The determination of boron, carbon, nitrogen and oxygen in metals and semiconductors by charged particle activation analysis (CPAA) is reviewed. It is shown that CPAA is a sensitive and accurate method suitable for the analysis of reference materials.
Several modifications are proposed of the established methods of iodine determination in serum. Prior to the actual analysis, the serum is lyophilized. This preliminary treatment permits the use of large samples. Through lyophilization human blood serum samples can easily be reduced to one-tenth of the original weight. Reduction is even more dramatic with materials from other than human origin. After irradiation the samples are subjected to chemical treatment in the presence of an iodine carrier and131I-labelled thyoxine. This procedure has been adopted for the determination of the iodine content and the chemical yield in one and the same radioactive measurement. The analysis technique itself consists of an open system Schöniger combustion. The open combustion allows the use of large samples; the gases evolved are absorbed upon their subsequent passage through potassium hydroxide and hydrochloric acid; the mineralization requires less than two minutes. After the addition of a substochiometric amount of silver nitrate, silver iodide is precipitated from an ammoniacal solution as a flat sample, which has been found ideally suited for high efficiency counting with a Ge(Li) detector. The spectrum gives evidence of an excellent decontamination from the38Cl,80Br and82Br activities. The iodine content can be calculated from the ratio of the photopeak areas at 364.5 keV and 442.7 keV corresponding to131I and128I, respectively. The chemical procedure requires a mere 15 min, and the recording of the γ-ray spectrum takes no longer than 30 min. The technique is not limited to serum only. It proved well suited for the analysis of many other types of biological material, e.g. human skin tissues.
The double irradiation technique, which is used to detect the production of a given nuclide from different chemical elements, by two different reactions in a polyenergetic neutron flux, cannot be generally applied. The application limits have been defined and calculated, based on the statistical fluctuation of the measured activities. The experimental verification and the practical applications of the calculated limits for activation analysis, and transmutation reaction cross section studies are discussed.
New circuits are presented to determine precisely the counting losses suffered in the entire gamma-ray spectrometer and to allow automatic correction for them even in the case of time-dependent counting rates as encountered in the measurement of short-lived radioisotopes. Experimental proof is given that the proposed circuitry allows accurate quantitative measurements in gamma-ray spectrometry. With counting rates up to 20,000 cps losses amount to less than 1.5%.