In order to determine the trace amounts (3 ng–100 ng) of lanthanoids in chondritic meteorites, new and convenient analytical procedures of radiochemical neutron activation method were presented. Applying these procedures to Antarctic meteorites, a total of ten lanthanoids (La, Ce, Nd, Sm, Eu, Gd, Tb, Tm, Yb, and Lu) were precisely determined in a sample of 50–100 mg. Considering several error sources such as counting statistics, collection of interferences, and determination of chemical yield, magnitude of overall error was estimated for each element.
A modified NiS fire-assay neutron activation method is developed for the determination of all platinum-group elements (PGEs) in mantle-derived xenoliths. This method is characterized by sub-ppb detection limits, <0.1~0.002 ppb procedural blanks and 7~15% analytical precision for PGEs. Analyses of PGE standard rocks indicate that this modified NiS fire-assay neutron activation method is as reliable as the method previously proposed for a large scale of samples. The capability of the method for the measurement of PGEs in the upper mantle is also illustrated by some exciting results obtained from mantle-derived xenoliths of Eastern China.
A simple and effective radiochemical procedure for radiochemical neutron activation analysis (RNAA) of ultra-trace siderophile
elements (Ru, Re, Os and Ir) and rare earth elements (REEs) in rock and meteorite samples is presented. To design the procedure,
several separation schemes of siderophile elements were examined by using radioactive tracers. By applying the procedure to
rock and meteorite samples, we have determined Ru, Re, Os, Ir and REEs, and confirmed that our values were in agreement with
the literature values. Our detection limits for Ru, Re, Os, La, Sm and Eu are significantly low compared with those for ICP-MS.
We determined uranium in silicate materials such as standard rocks and a meteorite by radiochemical neutron activation analysis. After activation with a cadmium cover, samples were subjected to radiochemical separation of uranium immediately. The gamma-ray intensity of239U was measured with a planar type pure germanium detector system. Our data are mostly consistent with the literature or reported values. Compared with a non-destructive method, the present method was found to improve the sensitivity by at least a factor of ten. Several errors which might be involved in our RNAA procedures were examined and their degrees were evaluated.
An analytical scheme of radiochemical neutron activation for the sequential determination of ultra-trace rare earth elements
(REEs) and highly siderophile elements (HSEs) in geological and cosmochemical samples is presented. Using this procedure,
several selected elements of REEs and HSEs were successively determined for geological reference samples and olivine crystals
separated from pallasite meteorites. Based on the data for geological reference samples, it was concluded that the procedure
presented in this study could yield data usable for cosmochemical discussion of the genesis of pallasite meteorites.
Simple and effective procedures for the determination of Re, Os and Ir by radiochemical neutron activation analysis are presented. Those elements are separated individually by distillation (for Os) and anion exchange techniques (for Re and Ir) for a single specimen. Reproducibilities of the data obtained by the present procedures are evaluated by replicate analyses of the Allende meteorite sample, and are deduced to be 3% for Re, 6% for Os and 4% for Ir (1). Detection limits for the present procedures are calculated to be 1 ppb for Re, 20 ppb for Os and 5 ppb for Ir. These procedures were applied to Antarctic meteorites and proved to work very effectively for the determination of trace Re, Os and Ir in chondrite meteorites.
In order to determine thorium and uranium traces in geochemical and cosmochemical samples, we developed an ICP-MS procedure, in which an anion-exchange step was introduced after sample digestion to separate major matrix elements, leading to decrease the dilution factor and increase the sensitivity for Th and U. The ICP-MS procedure was compared to the RNAA procedure which we recently developed for the same purpose. Both ICP-MS and RNAA procedures developed were found to yield similar detection limits (sub ppb) for Th and U.
Nickel sulfide (NiS) fire assay was used for the pre-concentration of Ir and Au in rock samples. The beads obtained after
fire assay were irradiated directly with neutrons to determine Ir and Au. To suppress the reaction of 58Ni(n,p)58Co, the fire assay was carried out by using a small amount of Ni (0.0625 g) and the NiS bead samples were irradiated by neutrons
with high Cd ratios. Analytical results of Ir and Au for rock samples were close to literature values, confirming that our
procedure of INAA with pre-concentration can be applied to rock samples for the determination of ppb to sub-ppb level of Ir
Applying rapid radiochemical separation of iodine coupled with epithermal neutron activation, we reliably determined trace amounts /6–95 ng/ of iodine in rock samples such as sedimentary rocks and chondritic meteorites. Our data on meteorites are in good agreement with literature values, but for sedimentary rocks the present data were systematically lower than the literature values. Based on the data from duplicate analyses of some sedimentary rocks and the results of tracer experiments employed parallel to the rock analyses, we concluded that the analytical results obtained in this work for sedimentary rocks were more reliable than the literature values.
Radiochemical neutron activation analysis (RNAA) was applied to geochemical and cosmochemical samples to determine trace amounts
of Mo and W. To determine the Mo concentration by NAA accurately, the contribution of the fission products of U should be
corrected. For that reason, we developed a simple and effective method, where a contribution of fissiogenic 99Mo was estimated by monitoring the ratio of uranium fission-product 99Mo to 133I. Mo concentrations corrected for fission with the W concentrations were consistent with the literature values, showing that
133I was found to be an effective monitor for fission correction. Detection limits are estimated to be 10 ppb for Mo and W and
30 ppb for U under the present experimental conditions.