Search Results

You are looking at 81 - 90 of 712 items for :

  • All content x
Clear All

Abstract  

A standardization method for NAA has been developed based on the activation equation and on isotope-related k i-values that are composite nuclear constants. This approach combines the simplicity of the absolute methods with nearly the same accuracy as that obtained by the relative ones. The k i-constants are calculated from the well measured k 0-factors and the neutron flux is determined as with the k 0-method. A computer program was developed for the determination of the neutron flux parameters and the concentration of the trace element. These calculations start with the measured activity of the radionuclides.

Restricted access

Abstract  

Two widely used neutron activation analysis (NAA) standardization methods (relative and k 0) have been validated at the Ghana Research Reactor-1 (GHARR-1) Centre using environmental and biological standard reference materials (SRMs). The samples were IAEA Soil-7 as an environmental sample, and NIST Orchard Leaves 1571 as a biological sample. The qualitative and quantitative analyses were done using a high resolution Canberra N-type high purity germanium (HPGe) detector. The accuracy and precision were evaluated for the elements analysed. The concentrations of most of the elements were found to be within 10% of the certified values. Precision was calculated from six replicate measurements and was found to be within 15%.

Restricted access

Summary  

The recently discovered universal functions for thermal and epithermal neutron self-shielding were adapted to NAA of cylindrical samples, expressing the magnitude as the product of a nuclear factor, a geometrical factor and the amount of the neutron absorbing element. The theory was tested and the nuclear factors were measured for 1 ml samples containing the halogens Cl, Br and I. Tests on samples containing these elements at a priori unknown concentrations, irradiated in a mixed thermal and epithermal neutron spectrum, showed that self-shielding as high as 30% could be corrected with an accuracy of about 1%, except in cases with significant epithermal shielding of one element by another.

Restricted access

Abstract  

The concentrations and distributions of total halogen (TX), extractable organohalogen (EOX) and extractable persistent organohalogen (EPOX) were determined in 20 kinds of yogurt specimens collected from Chinese supermarkets using neutron activation analysis (NAA) and gas chromatography equipped with a 63Ni electron capture detector (GC-ECD). The results indicated that the halogens in yogurt mainly existed as non-extractable organohalogen compounds. About 25–30% of EOX was EPOX. EOCl and EPOCl were the main organohalogen species in yogurt. The average concentration of the identified organochlorine, such as organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs), was below 4% of EPOCl.

Restricted access

Abstract  

The nonideality of the epithermal neutron flux distribution at a reactor site can be described by a 1/E1+ spectrum representation, with parameter being a measure of the nonideality. -values were determined in 3 typical irradiation positions of the TRIGA MARK II reactor of the Jozef Stefan Institute, Ljubljana, Yugoslavia, using the Cd-ratio for multi-monitor method. The simpler Cd-ratio for dual monitor method (monitors:197Au–94Zr) also yielded reliable results. This characterisation is of use in the k0-method of NAA, which is recently introduced at the Institute.

Restricted access

Abstract  

A Ni-Cr alloy was chosen as an in-house reference material for neutron flux measurement due to the well-known physical constants of the nuclides or interest and its low cost. The quantification of the Cr and Ni content was performed by neutron activation analysis (NAA), using certified reference materials from NIST as comparators. The concertrations and standard combined uncertainties were 19.32 ± 0.07 % for Cr and 80.2 ± 1.1 % for Ni, and the material is very homogeneous for Cr and moderate homogeneous for Ni.

Restricted access

Abstract  

An analytical expression has been developed to calculate the neutron self-shielding in a cylindrical sample using the elemental thermal neutron absorption cross sections, σ abs, and the newly-defined epithermal neutron absorption cross-sections, σ abs,ep. The σ abs,ep were measured experimentally for 13 nuclides and calculated from resonance parameters for 76 nuclides. Agreement between the two was good to about 20% in most cases. A spreadsheet program was written to use these nuclear parameters to perform iterative self-shielding corrections of concentrations measured by NAA. In cases with up to 30% self-shielding, the correction factors had uncertainties varying from 2% to 3%.

Restricted access

Abstract  

This paper deals with the osteoporosis model of New Zealand rabbits in order to study the function of inorganic elements for women patients with osteoporosis. The thirty cases of iliac crest are collected and determined using neutron activation analysis (NAA). The results show that the fluorine concentrations in the experimental group are higher than those in control group and the magnesium concentrations are significantly lower (P<0.001), but the concentrations of K, Na, Ca, Ba, Mn, Sr show no remarkable difference. Combined with the serum biochemical markers of bone formation and resorption, the physiological functions of some metal elements in bone are also discussed.

Restricted access

Abstract  

A pyrolysis-neutron activation analysis (NAA) procedure has been developed and applied to the speciation of arsenic in solid biological samples. The method involves the retention of the inorganic arsenic in the pyrolysis boat by the addition of NaOH, the volatilization and trapping of the organic arsenic on a cation exchange resin and the subsequent NAA of the resin for the determination of the trapped arsenic. The method, developed with the aid of radiochemically labelled arsenic compounds, has been applied to the determination of the ratio of inorganic to organic arsenic species in commercical shrimps as well as in NBS standard reference materials such as oysters and orchard leaves. The results show different relative amounts of inorganic arsenic content in the samples analysed. In the shrings the fraction of inorganic arsenic was of the order of 20%, in the oysters the inorganic arsenic consfituted 60% of the total arsenic concentration while in the samples of vegetable origin more than 98% of the arsenic was of inorganic nature.

Restricted access

Abstract  

Homogeneity of the existing (Virginia Tobacco Leaves CTA-VTL-2 (ICHTJ), Apatite Concentrate CTA-AC-1 (ICHTJ), Fine Fly Ash CTA-FFA-1 (ICHTJ) and candidate certified reference materials (CRMs) (IAEA-338 Lichen, IAEA-413 Algae, Spruce Shoots RMF II (Germany)) was studied by neutron activation analysis (NAA). Several samples of small mass (ca. 1 or 10 mg) taken from various containers were analyzed by instrumental NAA and the results for several elements were compared by Fisher's test and t-test with analogous series of results for samples taken from one container. In the second approach, sampling variance was estimated for some elements from overall variance and the components of analytical variance. The results were interpreted with the aid of Ingamells' sampling constant. Particle size distribution of the reference materials was also measured by several techniques. In addition quantitative determinations for some elements were performed and results compared with the certified values. The results of the present study were discussed with reference to suitability of CRMs to microanalytical techniques. It was pointed out that the term "microanalysis" itself is not always unequivocally understood and used.

Restricted access