Quantitative calibration and quality control have been a major bottleneck in microanalysis due to the lack of natural-matrix
CRMs certified at sample sizes compatible with those of unknown samples. In this paper, a solution is described to characterize
sampling behavior for individual elements, so as to identify elements homogeneous enough at stated sample size levels in given
CRMs/RMs. By using a combination of several nuclear analytical techniques, INAA-EDXRF-µPIXE, sampling behavior for individual
elements can be characterized at sample size levels from grams down to pg. Natural-matrix CRMs specifically for QC of microanalysis
may thus be created. Additional information in certificates of these new generation CRMs is imagined.
A neutron spectrum-independent compound nuclear constant, Iko, is proposed for fission interference corrections in reactor NAA by parametric method. Ik0 values for eight major fission interference cases, belonging to three different types, have been determined in six irradiation positions (withth/e 13,7–134) of three research reactors in our Institute. The general agreement among experimental Ik0 's from different irradiation positions and between experimental and calculated Ik0 values for the same interference case verifies the validity of the method. Calculated Ik0 values for all the possible fission interferences are tabulated. Interferences from238U(n,) and232Th(n,) reactions and reactor fast neutron induced238U(n, f) and232Th(n, f) reactions are discussed.
A post-Ko study of parametric reactor NAA is described including the determination and applications of working KoS for non-1/V reactions151Eu(n,)152Eu and176Lu(n,)177Lu; parametric corrections for235U fission, threshold reaction and -spectral interferences; and parametric normalizations for different counting geometries. The analytical significance, the principles, the experimental confirmations, and the application examples of these methods are briefly introduced.
A simple two step radiochemical separation scheme has been developed which permits the RNAA determination of As, Cd, Cu and Mo in biological matrices. The RNAA separation is applied following the INAA determination of at least 17 other elements in the same samples. Under our experimental conditions which included a four day decay period for handling and shipping from a remote reactor site, detection limits for As, Cd, Cu and Mo are 0.24, 6.6, 45 and 3.4 ng, respectively, in NBS biological standard reference materials SRM 1571 and 1567. Decontamination factors for the major spectral interferences,82Br,42K,24Na32P and122Sb have been determined and found to be sufficiently high for measurement of the elements of interest in most biological matrices. The overall INNA/RNAA procedure takes full advantage of high resolution Ge(Li) gamma-ray spectroscopy and involves minimal chemical processing.
Various theoretical and practical aspects of epithermal neutron activation analysis (ENAA) and fast-neutron-induced reaction interferences in conventional instrumental thermal neutron activation analysis (TNAA) have been considered. A new generalized advantage factor which reflects a practical improvement of detection limits in ENAA is proposed. In the determination of practical advantage factors, consideration is also given to the different irradiation channels available for the experiment in a given reactor, or even in several accessible reactors. Fast neutron reaction interference factors are tabulated for both ENAA and TNAA and examples are given of specific interferences in TNAA for some biological and geological matrices.
Authors:Ni Bangfa, Wang Pingsheng, and Tian Weizhi
Forty elements in IAEA-331 (Spinach), an intercomparison material, have been determined using NAA. Among them, 30 elements, Ag, Al, Ba, Br, Ca, Ce, Cl, Co, Cr, Cs, Eu, Fe, Hf, K, La, Mg, Mn, Na, Ni, Rb, Re, Sc, Se, Sr, Ta, Tb, Th, V, Zn and Zr were determined by INAA. A series of simple and quantitative radiochemical separation procedures were established for the determination of ten additional elements. Cd, Lu, Mo, Sb, Sm, Yb, U were determined by removing the major interfering nuclide82Br. Cu was determined by 0.048M NaDDTC/CHCl3 extraction from 1M HCl medium. As and P were determined using an inorganic exchange column of acid aluminium oxide (AAO). Integral counts from 80 keV to 130 keV contributed by Bremsstrahlung from32P -were used to evaluate the content of phosphorus.
45 elements have been determined by NAA in an IAEA Lake Sediment RM SL-3 Multitechniques were used to fully tap the potential of NAA in terms of the number of the determinable elements and the accuracy of each data.