Multi-element determination in silicate rocks by instrumental neutron activation analysis

Instrumental neutron activation analysis technique was applied for the determination of 20 elements in 54 silicate rock samples which belong to three sedimentary geological formations located in the western desert of Iraq. The samples along with USGS standards were irradiated in an IRT-5000 reactor at a neutron flux of 3.7·10¹³ n·cm^–2·s^–1 The following minor and trace element constituents have been determined: Na, K, Ca, Fe, Sc, Cr, Co, Zr, Ce, La, Nd, Sm, Eu, Tb, Yb, Lu, Hf, Ta, Th and U.     

Routine multielement instrumental neutron activation analysis of silicate rocks using short-lived radionuclides

By means of thermal neutron activation and countings on the small planar and large coaxial Ge(Li) detector, 13 elements are determined in various silicate rocks, using short-lived radionuclides with half-lives from 2 min to 15 h. A method of routine analysis with simple dead-time and pile-up correction is described and tested with the standard rocks AGV-1 and G-2.     

Optimization of instrumental neutron activation analysis for studying the chemical composition of silicate rocks

Software for optimization of instrumental neutron activation analysis of geological samples, preferentially silicate rocks, and a technique for evaluation and minimization of interference of gamma-ray lines are given. The maximum relevant signal-to-noise ratio was taken as a criterion for optimization by taking into account information available from a large number of lines in the gamma spectra studied.     

Optimization of instrumental neutron activation analysis for studying the chemical composition of silicate rocks

Software for optimization of instrumental neutron activation analysis of geological samples, preferentially silicate rocks, and a technique for evaluation and minimization of interference of gamma-ray lines are given. The maximum relevant signal-to-noise ratio was taken as a criterion for optimization by taking into account information available from a large number of lines in the gamma spectra studied. Received: 17 July 1997 / Revised: 7 November 1997 / Accepted: 16 November 1997     

Gamma-ray photopeak interferences found in the instrumental neutron activation analysis of silicate rocks

Data are tabulated to identify all major and minor gamma-ray interferences which may effect the area determinations of analytical photopeaks for all principle isotopes (of half life greater than about one day) encountered during the routine instrumental neutron activation analysis of silicate rocks. These photopeaks cover the energy range 60–1700 keV and are based on data abstracted from ERDTMANN and SOYKA.⁸ Interferences are listed down to relative intensities of 0.001% and include principle sum peaks. Photopeaks which are considered to be most reliable for routine quantitative analysis are identified.     

Application of intrinsic Ge detectors to the instrumental neutron activation analysis for rare earth elements in rocks and minerals

Improvements in the specifications of low-energy, intrinsic Ge detectors have enabled the routine determination of the concentrations in geological samples of eleven rare earth elements, including lanthanum, without using a Ge(Li) detector. The efficiency of an intrinsic Ge detector is compared with a high-efficiency Ge(Li) detector, and a quantitative assessment of the effect of X-ray and gamma-ray interferences is given. Rare earth element abundances in four U. S. G. S. standard rocks have been determined.     

Multielement analysis of Northwestern Nigerian rocks by instrumental neutron activation analysis

Rock samples from seven different locations in northwestern Nigeria were analyzed by reactor instrumental neutron activation analysis and Ge(Li) gamma-ray spectrometry. Concentration values were obtained for 18 elements (As, Ce, Co, Cr, Cs, Eu, Fe, Hf, La, Lu, Sc, Sm, Sr, Ta, Tb, Th, U, Yb). The geochemical implications of the results are discussed.     

Correcting for uranium fission in instrumental neutron activation analysis of high-uranium rocks

Failure to correct for fission products of²³⁵U is shown to result in significant errors in the measured concentrations of La, Sm, Nd, Ba, Zr, and Mo by Instrumental Neutron Activation Analysis of high uranium rocks. Measured and calculated correction factors are presented as the ratio of the fission product to parts per million by weight of uranium in the rock. Potential errors in petrogenetic interpretations of uncorrected data are outlined.     

Determination of chlorine in silicate rocks by neutron activation analysis

A simple radiochemical neutron activation analysis scheme has been developed for the determination of chlorine in silicate rocks. The method involves a 15-min thermal neutron irradiation of rock powder followed by a quick separation of ³⁸Cl as AgCl, and Ge(Li) spectrometry. Chemical yield, normally ranging between 95% and 100%, is monitored gravimetrically through the recovery of AgCl. The procedure has been tested on several geochemical standards to assess its accuracy and precision. The values obtained for standard rocks agree with the literature values. At the 100-ppm level, the analytical precision for chlorine is within ±5% (2σ).     

Single-crystal trace element analysis in rock-forming minerals by instrumental neutron activation analysis

We have developed an INAA techniques for analyzing single crystals extracted from rocks. Trace element contents have been measured in a large variety of mineral species, as well as isotopic ratios of some REE in minerals related to natural fission reactions. The sensitivity of INAA allows to avoid the main shortcomings of usual mineral geochemistry: (1) only very short quantities of minerals are needed (down to a few g), so that even very sparse minerals could be analyzed, (2) purity of minerals is carefully checked, and (3) the heterogeneity of a population may be studied. The method is especially useful when applied to minerals acting as tracers for some element families, e.g. REE in Ca-bearing minerals (fluorite, apatite, titanite, gamet) and Zr-bearing minerals, or chalcophile elements (Co, Ni, As, Sb, Mo, Ag, Au and Se) in sulfides. We present an application of the method to the Oklo U deposit in Gabon showing that features outlined above are of special interest for the study of hydrothermal processes.     

Multiparameter coincidence spectromety applied to the instrumental activation analysis of rocks and minerals

An instrumental method for activation analysis based on multiparameter coincidence spectrometry is described. Practical considerations of our X- and - coincidence systems are presented. The main applications of geochemical interest are the non-destructive determinations of tin in granitic rocks and iridium in ultra-basic rocks. Some other applications to the activation analysis are proposed.     

A group separation scheme for radiochemical neutron activation analysis for 24 trace elements in rocks and minerals

A group separation scheme has been developed for radiochemical neutron activation analysis for Ca, Cu, Zn, Ga, Rb, Sr, Zr, Sb, Cs, Ba, La, Nd, Sm, Eu, Gd, Tb, Ho, Tm, Yb, Lu, Hf, Ta, W and Th in a wide variety of silicate rocks and minerals, especially ultrabasic rocks and mafic minerals. The samples are decomposed in a hydrofluoric acid-nitric acid mixture in a PTFE-lined bomb. The soluble fluorides (Cu, Zn, Ga, Rb, Zr, Sb, Cs, Ht, Ta, W and Pa) are separated into three groups of elements by sequential elution from a cationexchange resin. The insoluble fluorides (Ca, Rb, Sr, Cs, Ba and REE) are dissolved and purified from interfering iron and scandium activities by extraction with tri-n-butyl phosphate. If necessary, the four main groups can be purified further from interfering activities such as ⁵⁹Fe, ⁵¹Cr and ⁶⁰Co. The accuracy and reproducibility of the procedure were tested by repeated analysis of U.S. Geological Survey standard granite G-2, andesite AGV-1 and dunite DTS-1.     

Interference from uranium in neutron activation analysis or rare-earths in silicate rocks

A direct nondestructive method of analysis for²⁴¹Am utilizing photon counting and self-absorption correction factors is presented. The method gives favorable agreement for samples analyzed by radiochemical separation procedures and alpha particle spectrometry. The comparison was made over a range of approximately five orders of magnitude of²⁴¹Am concentrations. The method is reliable and relatively simple. Sensitivity for a ∼5-g sample and a counting intervals of 60 000 s is ∼0.2 pCi/g with an uncertainty of ±22%, which decreases to ±11% for increased counting intervals of 150 000 s and an increased sample size of ∼20 g.     

A study of flux monitoring for instrumental neutron activation analysis

The accuracy of instrumental neutron activation analysis is dependent upon measurement of the neutron flux to which samples are submitted. Flux monitoring techniques described and evaluated include: target cooling water activity, BFa counters, plastic scintillators, and a simple reference sample system. Evaluation is made on the basis of results obtained for oxygen analysis using primary standard materials. The superiority of the reference sample system for flux measurement during irregular neutron flux production is shown.     

Errors in instrumental neutron activation analysis

Equations are derived for the statistical and systematic error in INAA based on single photopeaks. They may serve to predict the applicability of the method or to judge data obtained under well-known conditions.     

Erros in instrumental neutron activation analysis

Equations are derived for the statistical and systematic error in INAA. It is possible to use them for the definition of limits of decision, detection and determination.     

Rare earth element determination in silicate rocks using neutron activation analysis and mass spectrometry

A pre-irradiation group separation procedure for the quantification of 11 to 13 rare earth elements (REE) in geological materials by neutron activation analysis, with yield determination by mass spectrometry isotope dilution analysis of Sm and Nd, is described. Utilization of the shorterlived isotopes of the REE allow sufficient data for most geochemical studies to be obtained within one day of irradiation, although where necessary additional information may be obtained following a decay period of three to four weeks. Analysis of selected USGS rock standards shows the method to be both accurate and precise.     

Industrial applications of instrumental neutron activation analysis

Neutron activation analysis is shown as a useful diagnostic technique in semiconductor industry. A better acceptance of the method for applications in industry has been achieved through a specialized analytical service. Its main application is the characterization of high purity silicon in all stages of production. Irradiation of large sample volumes allowes a very sensitive detection of impurities in silicon with detection limits down to 10^–16 g/g. Other applications discussed are the analysis of silicon carbide, quartz, pure water and titanium. Special techniques described are autoradiography, depth profiling and surface analysis. In semiconductor process technology NAA was used to monitor contamination of silicon wafers.     

A new approach to single-comparator instrumental neutron activation analysis

A new parametric approach to single-comparator instrumental neutron activation analysis (INAA) at the University of Missouri Research Reactor (MURR) was investigated. A detailed MCNP steady-state model of the MURR core was developed using the latest neutron data libraries to compute the continuous-energy neutron flux distribution. Intrinsic reaction rates were predicted by coupling the computed local flux distribution to the isotopic (n, γ) excitation functions for a range of elements present in standard reference materials (SRM). Using the predicted (n, γ) reaction-rates, the concentrations for the various elements were determined. The method worked well for all nuclides tested, including those with cross sections that are not proportional to 1/v such as Lu and Eu with agreements for most elements within 5% of the reference value.