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- Author or Editor: R. Van Grieken x
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Abstract
The half-life of28Al was redetermined on aluminium samples of different origin. Three different counting techniques were applied. The availability of highly purified samples (up to 99.9999%), the use of very fast electronic counting equipment and a complete automatisation allowed a good precision to be obtained in the final result of 2.2405 min.
Abstract
Energy-dispersive X-ray fluorescence analysis was applied for the analysis of hair. The hair samples were digested in a mixture of nitric and perchloric acid and the heavy metals were precipitated with ammonium pyrrolidine dithiocarbamate. The accuracy, precision and recovery of the method for the elements Fe, Ni, Cu, Zn and Pb were evaluated through the analysis of a standard hair sample. The procedure was applied to the analysis of hair from an occupationally exposed group of Sudanese workers and a control group. The hair of the exposed group showed a range of 80–550 ppm Fe, 6–12 ppm Cu, 57–190 ppm Zn and 70–3700 ppm Pb, while that of the control group had a range of 60–310 ppm Fe, 7–22 ppm Cu, 89–170 ppm Zn and 3–17 ppm Pb.
Abstract
A fast (10 min), non-destructive simultaneous determination of silicon and phosphorus in cast iron and steel by 14 MeV neutron activation was developed. The 1.78 MeV28Al activity (T=2.24 min) induced by the reaction28Si(n, p)28Al is counted on a NaI(Tl) detector. Two measurements are made to correct for the 1.81 MeV56Mn activity (T=2.58 hr) from the iron matrix. However,28Al is also produced via31P(n, α)28Al. By (n, 2n) reaction, phosphorus yields also30P (T=2.6 min), the 0.511 MeV annihilation radiation of which is counted by two opposite NaI(Tl) detectors in coincidence. Again, two successive coincidence measurements are carried out in order to take into account the53Fe activity (β+; T=8.9 min) from54Fe(n, 2n)53Fe. The28Al measurement is appropriately corrected via the computed phosphorus content. An oxygen flux monitor was used to normalize to the same flux. Nuclear interferences have been examined. Special attention has been paid to the presence of copper. The standard deviation for phosphorus being as high as ca. 0.09% P for a single determination, this technique can only be practical as an independent phosphorus analysis for high phosphorus cast irons. The precision on the28Al measurement is 5% relative for 0.2% Si and 2.5% above 1% Si.
Abstract
The neutron flux distribution in the vicinity of 30, 20 and 10 mm diameter targets is measured by irradiating concentric ring-type iron monitors at different distances from the target and counting the induced56Mn activity. Considering the many uncertainties, satisfactory agreement was found between theory and experiment.
Abstract
The effects of inaccurate sample sizes and sample positioning on 14 MeV neutron activation analysis results are estimated for 30, 20 and 10 mm diameter targets. It appears that axial positioning is the most critical parameter and that using a larger tritium target will yield an overall improvement of the reproducibility.
Abstract
To sulfide geothermal waters from the French Pyrenees region and bicarbonate and chloride waters from the French Vosges area, all of the following analysis techniques were applied in order to compose a broad inventory of trace elements: (1) for the dissolved material: neutron activation analysis after a freeze-drying step using a very short cycle (I), short cycle (II) or long cycle (III), neutron activation after co-crystallization on 1-(2-pyridylazo)-2-naphthol (PAN) using a short cycle (IV) or long cycle (V), X-ray fluorescence after co-crystallization on PAN (VI) and spark source mass spectrometry after evaporation on graphite (VII) or preconcentration on PAN, and, (2) for the filtered or suspended material: neutron activation using a very short (VIII), short (IX) or long cycle (X) and X-ray fluorescence (XI). Altogether, on the average some 30 elements could be determined above the detection limit in solution and 15 in suspension. It appeared, however, that for procedures (I), (II), (IV), (VI), (VIII) and (XI) the investment of time and cost had not been efficient enough. Invoking only procedures (III), (V), (IX), (X) and for low salinity geothermal waters only: (VII), the number of elements detected was almost as large.
Abstract
The isotopes 137Cs and 210Pb were determined in sediment cores originating from the floodplain of the river Yamuna (the largest tributary in the Ganges river system, India). Sampling was done at five locations: Sharanpur (next to the Himalayan foothills), Delhi, Jagmanpur, Hamirpur and Allahabad, where Yamuna meets the Ganges. The rate of sedimentation derived from both techniques, 137Cs and 210Pb, appears to be quite similar. At the station Sharanpur the highest rate of sedimentation (5.99 cm/y) was noticed, most probably due to deforestation and other human influences in the Himalayan regions, while the lowest rate was observed in Hamirpur (2.48 cm/y). All the five cores studied showed a 137Cs peak of 1963, due to radioactive fallout, caused by weapon tests. The three upstream stations (Sharanpur, Delhi and Jagmanpur) showed a 137Cs peak due to the Chernobyl event. These measurements reflect that Chernobyl debris have been transferred to the low latitude river system across the Himalayas.
