Search Results

You are looking at 101 - 110 of 712 items for :

  • All content x
Clear All

Abstract  

Since its launching in the mid-70s, thek 0-standardization of NAA has been implemented and used in a growing number of laboratories worldwide. In the present paper, a survey is given of the situation in Europe, where the method or its associated subroutines are now operational in 22 industrial, governmental and university research centres spread over 12 countries plus IRMM of the European Union. In quite some of these places, not only practical applications are going on, but — as also reported here — further developments of the methodology are dealt with as well. These are related to such topics as the refinement of the fundamentals, the extension and improvement of the nuclear data library, the calibration of the Gedetector and of the neutron irradiation facility, the care for quality control/assurance and the upgrading of software for PC or mainframe.

Restricted access

Summary  

The determination of arsenic at natural levels in biological materials remains difficult. Many analytical techniques cannot detect the low levels present in typical biological tissues and other techniques suffer from interferences. This paper reviews uses of neutron activation analysis (NAA) at NIST to determine nanogram amounts of arsenic in biological reference materials with radiochemical (RNAA) or instrumental (INAA) procedures. INAA is compromised by high activities from 24Na, 82Br, and 32P that may be formed during irradiation of biological tissues, and result in detection limits as high as 0.1 mg. Lower detection limits have been achieved using state-of-the-art gamma-ray spectrometry systems in INAA and a variety of procedures in RNAA. These techniques and procedures were applied recently at NIST to the determination of arsenic in urine, nutritional supplements, and total diet samples.

Restricted access

Abstract  

The software ASPRO-NUC is based on new improved algorithms suggested and tested in the laboratory and intended for routine analysis. The package consists of the program ASPRO for gammaray spectra processing (peak search, multiplets deconvolution by means of method of moments, computation of correction coefficient for geometry and material of radioactive source), a program for isotope identification and a program for NAA by means of relative standardization. All output information is loaded into a data base (Paradox v.3.5 format) for supporting of queries, creation of reports, planning of routine analysis, estimation of expenses, supporting of network of analytical survey, etc. The ASPRO-NUC package also includes a vast nuclear data base containing evaluated decay and activation data (reactor, generator of fast neutrons, Cf-252 source). The data base environment allows for easy integration of a gamma spectrometer into a flexible information shell and the creation of a logical system for information management.

Restricted access

Abstract  

A study is made of the correction, in k0-standardized NAA, for interferences caused by fast neutron induced threshold reactions, second order reactions and235U-fission. The following examples are elaborated: determination of the Cr and Sc concentrations in a reference human serum, corrected for the54Fe(n,)51Cr and44Ca(n,;; n,)46Sc interferences, respectively, and the determination of Zr, Cs, La, Ce, Nd and Sm concentrations in USGS BCR-1 and G-2, corrected for235U(n, f) interference. A detailed uncertainty analysis and a comparison of the analytical results thus obtained with other literature values proves that the interferences can be accurately corrected for by employing the usual neutron flux monitors in the k0-method, namely a Zr-foil and a dilute Au–Al alloyed wire.

Restricted access

Abstract  

Commercially available7LiOH was used for collecting volcanic gas samples on the island of Vulcano, Southern Italy, to determine trace elements by NAA. The high -background activity, which is induced when NaOH solutions are used as collecting agents was avoided in this way. While several elements (Cl, Br, I, As) could be determined in the collected samples, activation products of impurities in7LiOH produced considerable -background and this prevented the determination of other trace elements. An ion-exchange procedure for reducing impurities in7LiOH solutions, in particular of Hg, Ta and W, was then developed and is described here. This procedure, supplemented by steps to eliminate interference from18F in the irradiated samples due to small amounts of6Li in the7LiOH employed will allow very sensitive determinations of further trace elements in volcanic gases.

Restricted access

Summary  

Major and trace elements in soil and plant samples, including standard reference materials were determined by means of neutron activation analysis (NAA) and inductively coupled plasma-mass spectrometry (ICP-MS). The analytical procedure for NAA utilized dried powder samples. The concentration of iodine in soil samples was determined by radiochemical NAA. The irradiated samples were cooled and then counted with a Ge gamma-ray detector connected to a multi-channel analyzer. For ICP-MS analysis, the samples were decomposed by microwave digestion with an acid mixture. The concentration of I in the soil samples was measured by ICP-MS after separation by ignition. The analytical values for most elements in the environmental samples by both methods were in good agreement, whereas sample treatments were different. Measured value of Zr in the soil samples by ICP-MS was about 50% lower than that by NAA. It should be assumed that some minerals of Zr in soil particles were not entirely dissolved by the acid mixture. Analytical results of Cd for three different Cd levels in unpolished rice flour samples (NIES 10-a, b and c) determined by ICP-MS were in agreement with certified values. The concentration of Cd in the sample with the lowest Cd level, as determined by NAA with 57% counting error, was 3 times higher than the certified value.

Restricted access
Journal of Radioanalytical and Nuclear Chemistry
Authors: P. Geetha, N. Karunakara, Ujwal Prabhu, P. Ravi, J. Sudhakar, Nicy Ajith, K. Swain, R. Acharya, and A. Reddy

Abstract  

Instrumental and preconcentration methods of neutron activation analysis (NAA) have been standardized for the determination of concentration of iodine in grass and cow milk samples, respectively. To study the transfer of iodine from grass to milk, known quantity of grass spiked with potassium iodide solution was fed to a cow. The spiked grass samples and milk samples, obtained from the cow after the ingestion of spiked grass, were collected. Iodine was separated from the milk samples chemically using Dowex 1X8 anion exchange resin. Spiked grass and ion exchange resin samples were neutron irradiated and radioactive assay was carried out using a 45 % relative efficiency HPGe detector coupled to an 8k channel analyzer. Iodine concentrations in spiked grass samples were found to be in the range of 1,487–2,002 mg kg−1. Concentration of iodine in milk after 12 h of feeding the cow with spiked grass was 871 ± 56 μg L−1 which was reduced to 334 ± 32 μg L−1 after 48 h.

Restricted access

Abstract  

An investigation is made of the importance of (n,,n, ) second-order reaction interferences in reactor neutron activation analysis (NAA), in addition to the commonly considered (n, , ; n, ) interferences. The algorithms for the calculation of the interference are derived from the Bateman-Rubinson equation, taking into account the formation of all m-and g-states involved bum-up effects, and the growth of the interfering radionuclide after irradiation due to a mother-daughter relationship. The following practical cases are examined in detail:138Ba 140La (detemination of La in presence of excess Ba),139La 141Ce (Ce in La),164Dy 166Ho (Ho in Dy),186W 188Re (Re in W) and192Os 194Ir (Ir in Os). A computer search was done for the nuclear data involved in the computation. For139La[(n,; n,; )+(n,; ; n,)]141Ce, and164Dy[(n,; n,; )+ (n,; ; n,)]166Ho experimental checks were performed in the Budapest Research Reactor, which confirmed the calculations showing that the (n,; n,; ) interference gives the largest contribution to the apparent concentration of Ce in La and of Ho in Dy, respectively.

Restricted access

Abstract  

Reactor channel characterization is commonly performed by irradiating bare and cadmium-covered “fluence rate monitors”, avoiding as much as possible the use of irradiation vials and spacers to position the monitors inside the channel. However, in routine k 0-Neutron Activation Analysis often samples are packed in small polyethylene vials prior to irradiation. This work aims at studying the impact of typical NAA polyethylene vials (~1 mm wall thickness) on the determination of the f and α channel-specific parameters through the “Bare”, “Cadmium-Covered” and “Cadmium-Ratio” methods. The impact of these vials on each method was studied for 3 irradiation channels of the Belgian Reactor 1 at SCK·CEN (Mol, Belgium) with low to high f and α-values. The net impact was 1% on each parameter. Inconsistencies between the different methods were found when the impact of the polyethylene was neglected, implying that all determination methods must be pooled and thin monitors should be used for an accurate channel characterization.

Restricted access

Abstract  

The nuclear and spectral interferences in the 14 MeV neutron activation analysis (NAA) of gold from Romanian auriferous alluvial sands, concentrates and rocks have been studied and the optimum of activation, cooling and measuring times was determined for a maximum peak-to-background ratio for gold. The contribution of the nuclear interfering elements in the samples, Hg and Pt, to the concentration of gold has been calculated and, concluded that the nuclear reactions 197Au(n,2n)196Au, 197Au(n,2n)196mAu and 197Au(n,n')197mAu can be used for gold determination, with minimal errors. Using the nuclear reactions 197Au(n,n')197mAu and 197Au(n,2n)196Au the spectral interferences are minimal and are due to Rb, Ti and V for a short irradiation and to Se for a long one. Two methods of fast gold determination were proposed for auriferous alluvial sands and rocks in the range of 20-2500 ppm, under the optimum conditions established so that the systematic errors of analysis due to the gold accompanying elements can be considerably diminished. For measuring the induced gamma-radioactivity in the samples either a short irradiation (25 seconds) with a NaI(Tl) detector or a long irradiation (3000 seconds) with a Ge(Li) detector were used.

Restricted access