[en] Abstract only

[en] The presence of uranium in a sample enhances the true values of La, Ce, Nd, Sm determined by INAA if appropriate corrections are not made for the interference. The enhancement of the true values is produced for the (n,γ) activation products of these elements, viz. ¹⁴⁰La, ¹⁴¹Ce, ¹⁴⁷Nd, ¹⁵³Sm, are also produced from the fission of ²³⁵U (approximately 0.72% natural isotopic abundance) even when La, Ce, Nd, Sm are totally absent in the given sample. In a 5 hour irradiation 1 μg of U is found to be equal to 0.28 μg of Ce and 0.23 μg of Nd while the equivalent La is found to be dependent upon the delay from the end of irradiation to sample counting time. A numerical procedure is given to correct for these interferences. Spectral interferences from fission and (n,γ)β^- products of uranium in the determination of other trace elements by INAA are also investigated. For the determination of uranium, the 278 keV gamma-ray of ²³⁹Np was found to be best. (author)

[en] The techniques employed to measure Th concentrations in acrylic (PMMA) samples at a level of a few tens of ppt are described. Measurements on eleven different acrylic samples yielded a mean Th concentration of 40+-20 ppt. (author)

[en] Improvements in the detection limits of thorium and uranium in acrylics by neutron activation analysis are described. The average of results from 10 g samples was found to be higher than the results from 450 g samples taken from the same acrylic sheet. Using eighteen large (450 g) samples from a single sheet of acrylic gave an average value of 3.2±0.3 pg/g thorium and 1.1±0.7 pg/g uranium. Interpretation of the results is discussed. Epithermal neutron activation with Cd shielded irradiations did not improve the detection sensitivity for thorium. (author) 13 refs.; 2 figs.; 3 tabs

[en] Twenty-four elements in six food spices were estimated by non-destructive instrumental neutron activation analysis. The problems in determining of Cu were discussed. (author)

[en] The intensity of the 1001 keV γ-ray occurring in the decay of ^234mPa in equilibrium with natural uranium sources is found to be (0.818 ± 0.30)%. This value is in agreement with a recent measurement employing depleted uranium sources, but does not agree with earlier reports employing radiochemically pure sources. (author) 9 refs.; 1 tab

[en] A reactor-detector combination has been calibrated for routine determination of trace elements by instrumental neutron activation analysis using the semi-absolute method with flux corrections. The reproducibility of the calibration constants is studied using the standard rock AGV-1 for the activities ¹⁴⁰La, ¹⁴¹Ce, ¹⁵³Sm, ¹⁶⁰Tb, ¹⁵²Eu, ¹⁷⁵Yb, ¹⁷⁷Lu, ¹³¹Ba, ⁶⁰Co, ⁵¹Cr, ¹³⁴Cs, ¹⁸¹Hf, ²³³Pa, ⁴⁶Sc and ¹⁸²Ta. The results show that a calibration reproducibility with a relative precision of better than 5% can be achieved in many of the cases without any special precautions. To study tha applicability of the calibration constants, concentrations of the corresponding elements have been determined in standard rocks, G-2, W-1 and GSP-1 and are compared with the recommended values. (author)

[en] Measurements have been made of the thorium, uranium and potassium concentrations in a variety of materials. The methods of direct γ-ray counting and neutron activation analysis have been employed, and cases of secular disequilibrium most notably in aluminum have been identified. Several comprehensive tables of results are provided. (orig.)

[en] The rise of neutron activation analysis (NAA) as a tool in geochemical research has parallelled advances in detector, multi-channel analyzer, and computer technology. Micro-computers are now being integrated into NAA systems, and gamma-ray spectrometer instrumentation is evolving towards direct-reading systems. The investigator is faced with a wide range of possibilities and choices when equipping or re-equipping a laboratory. The geoscientist is provided with an overview of the available instrumentation and what soon may be feasible. (L.L.)

[en] A γ-ray peak attributed to the deexcitation of the first excited state of ⁵⁰Ti has been detected from vanadium metal by a large, low background intrinsic Ge detector operating in a salt mine. The partial half-life for the electron capture decay of ⁵⁰V to the first excited state of ⁵⁰Ti has been estimated to be 1.2/sub -0.4//sup +0.8/ x 10¹⁷ yr. A limit on the partial half-life for β^- decay is also obtained