Total oxygen, in fourteen rock standards and three ores, was determined with an experimental set up employing cyclic activation analysis using a 14 MeV neutron generator gamma-spectroscopy and NaI(T1) detectors.
Lichen (species Trypethelium Eluteriae) is analysed for different elements. Nondestructive instrumental neutron activation analysis is employed for the multielemental analysis. Gamma-ray spectrometry is used for the identification and quantitative estimation of elements. Concentrations of 24 elements are reported. Gamma-ray spectrum of the lichen irradiated for 16 hours, delayed for 10 days, and counted for 10 hours on a 50 cm3 coaxial Ge(Li) detector is given.
Elemental abundances determined by neutron activation usually result from comparisons of gamma-ray intensities in samples (unknown concentrations) and standards (known concentrations). If the samples and standards have large differences in gamma-ray intensity significant errors arise from coincidence losses resulting from pulse pile-up. The resolving times (the Wyttenbach factor of 2/) of four semiconductor germanium detectors coupled to three different multichannel analyzers used for routine activation analysis are determined with and without pile-up rejector. The errors caused by pulse pile-up in trace element abundance determination of different geological samples are tabulated.
Indium (10–15,000 ppm) and tin (20–90%) are quantitatively determined in cassiterite samples by instrumental (thermal) neutron activation analysis, using semiconductor detectors and gamma spectroscopy. Precision is 7% or better for In and 5% or better for Sn. The detection limit is 2 ppm for In and 0.4% for Sn in Mexican cassiterites.
Spectroscopically pure, 99.999% silicon dioxide (SiO2) from five different companies was analysed for trace element impurities by instrumental neutron activation analysis using semiconductor detectors and gamma-ray spectrometry. If large amounts of these purified SiO2 samples are added to, geological samples with low trace element contents e.g., mineral separates such as quartz, feldspar and olivine, the trace element contents of the SiO2 are a significant contaminant.
Samples are irradiated cyclically with a 14 MeV neutron generator and counted only once at the end with NaI(Tl) and Ge(Li) detectors. Results are reported from experimental work done on fourteen standard rocks and three ores. The usefulness of the built-up activity due to cyclic irradition together with flux corrections is demonstrated by simultaneous estimation of other major elements.
Five second generation USGS standards AGV2, BCR2, BHVO2, DTS2 and GSP2 were analyzed for trace elements by instrumental neutron activation analysis. Abundances of the rare earth elements La, Ce, Nd, Sm, Eu, Tb, Yb, Lu and eight other elements Co, Cr, Cs, Hf, Na, Sc, Ta and Th were determined in all samples, except for DTS2 which was analyzed only for Co, Cr, Na and Sc. Experimental precision and accuracy were evaluated. In general abundances of trace elements in this new generation of USGS standards are similar to the earlier standards. Abundances of Cr are, however, substantially higher in AGV2, BCR2, GSP2 and especially DTS2.
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 activities140La,141Ce,153Sm,160Tb,152Eu,175Yb,177Lu,131Ba,60Co,51Cr,134Cs,181Hf,233Pa,46Sc, and182Ta. 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 the 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.
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 comes about because the (n, γ) activation products of
these elements, viz.140La,141Ce,147Nd,153Sm, are also produced from the fission of235U (∼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 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
is also investigated. Uranium is found to be determined best using the 278 keV gamma-ray of239Np.