鉄質イン石中の宇宙線生成極微量チタン,バナジウムの測定

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The concentration of cosmic-ray-produced stable nuclides of titanium and vanadium in iron meteorites, especially in the Grant meteorite, were determined by a surface ionization solid source mass spectrometer using an electron multiplier. A triple filament technique was applied for both elements. A rhenium ribbon was applied to the center(ionizing)filament and for titanium two tantalum ribbons and for vanadium tungsten ribbons to the side(sample)filaments respectively. Repeated experiments using 0.1-1 microgram quantity of reagent titanium and vanadium indicated a satisfactorily high reproducibility throughout the cource of this work. The results with the reagent titanium and vanadium were in a good agreement with the determinations by Hogg and by White et al respectively. Using about one gram of the iron meteorites specimen, the extractions of titanium and vanadium were performed simultaneously in a systematic wet chemical separation scheme with potassium, calcium, chromium, and manganese. For the determination of the absolute contents of cosmogenic nuclides, isotopic dilution analysis was made using enriched 46Ti for titanium and reagent vanadium for vanadium as the spikes. The determination of above nuclides were possible with sufficiently low contamination of natural elements at the levels of 0.1 ppm for titanium and 0.01 ppm for vanadium. The enrichment in 49Ti was observed most prominently in the mass spectrum of titanium samples separated from the iron meteorites. At the same time the other products, 47Ti and 46Ti were also determined with a high reproducibility. 50Ti was also measurable though the error, ±30%, was still high. Examples of the data of cosmic ray produced stable titanium and vanadium are as follows;[unit:×1013 atoms/g. of meteorite]Aroos: 46Ti 4.00, 47Ti 4.85, 49Ti 7.70, 50Ti 0.27, and 50V 5.45. We have completed a set of data at A=50which includes new data of 50Ti and 50V, and our previous data of 50Cr and also 50V.The distribution of these three isobars provides useful measure in the spallation systematics in meteorites. Two parameters, R and S, in the semi-empirical equation of spallation cross section, Inσ(Z)=-R(Z-SA)2+K, were calculated to be 1.5±0.2 and 0.469±0.001 respectively. The radiation age of Aroos was estimated applying widely ranged pairs of both radioactive and stable nuclides, which were now all available. Each age derived from different isobaric pairs agreed well and this may suggest the negligible effect of space erosion or similar mechanisms such as many small collisions in space. In Grant, the depth effect was found to be effectively negligible with 49Ti and 50V in contrast to lighter nuclides such as Ne and K. Any irregurality in a curve of spallation yield vs.ΔA was not observed in mass range of 46-49. The experimental procedure is described in detail.
日本質量分析学会の論文

鉄質イン石中の宇宙線生成極微量チタン,バナジウムの測定

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