Search Results

You are looking at 111 - 120 of 7,410 items for :

  • All content x
Clear All

Abstract  

The use of high-resolution Ge(Li) detectors in non-destructive instrumental neutron activation analysis (INAA) of mineral materials makes possible the simultaneous determination of a number of trace elements. In routine applications of INAA the use of a multi-element standard (MES) has proved to have advantages over a set of standards for each determined element. An MES has been prepared containing 8 trace elements mixed in a suitable proportion and giving, after neutron activation, long-lived γ-emitters, the γ-ray lines of which regularly occur in the γ-ray spectra of silicate mineral materials. This method has been used in the determination of Sc, Cr, Co, Rb. Cs, Eu, Hf and Th in samples of standard rocks and moldavites.

Restricted access

Abstract  

Trace amounts of transition elements (Co, Cr, Cu, Fe, Mn and V) and other seven elements in optical waveguide samples were determined by INAA. The contents of impurities in ultra-pure materials are less than those of high-purity materials and of G.R. grade. The increase of contamination of trace transition elements and iridium from furnace or crucible are observed in the production of optical glass fibers. Up to seventeen elements were determined in five NBS biological standard reference materials: Oyster Tissue: SRM-1566, Brewers Yeast: SRM-1569, Spinach: SRM-1570, Orchard Leaves: SRM-1571 and Tuna Fish, and in four Japanese biological standard reference materials: Tea Leaves B&C, Pepperbush and Shark Meat. The analytical results in NBS and Japanese standard reference materials are in good agreement with published values and certified values by NBS.

Restricted access

Abstract  

Sodium tartrate dihydrate, lactose monohydrate, potassium citrate monohydrate, and calcium oxalate monohydrate are commonly used as primary standards for methods that determine water content. Identification of the type of water of hydration (channel, lattice, or ion associated) is provided herein for each standard based upon thermogravimetry/differential thermal analysis (TG/DTA) and dynamic vapor sorption data. Sodium tartrate dihydrate was found to be a mixed hydrate, containing 1 mol of channel water and 1 mol of lattice water. Lactose monohydrate and calcium oxalate monohydrate were both determined to contain lattice water of hydration. Potassium citrate was shown to exist as an ion-associated hydrate. Also provided is a discussion of how hydrate type, thermal properties and hygroscopicity may impact suitability of each compound for use as a standard.

Restricted access

Abstract  

An internal mono-standard method has been proposed for multi element analysis. This method gives the relative concentration of the elements in a sample of non-standard shape and size. It utilizes an in-situ relative efficiency calibration and hence, does not need the cumbersome procedures, otherwise required to correct for -attenuation in the sample. To validate this method, the relative concentration of elements in IAEA RM's SL-3 and Soil-7 were analyzed with sample amounts ranging from a few milligrams to grams. The samples were counted in different non-specific geometries. The results are in good agreement with the recommended values, suggesting that this methodology could be applied for the analysis of samples of non-standard size and shape, and in principle, for the analysis of large samples.

Restricted access

Abstract  

An external standard method for PCR quantification of HCMV was reported. [-32P]dATP was used as a tracer.32P-labelled specific amplification product was separated by agarose gel electrophoresis. A gel piece containing the specific product band was excised and counted in a plastic scintillation counter. Distribution of [-32P]dATP in the electrophoretic gel plate and effect of separation between the32P-labelled specific product and free [-32P]dATP were observed. A standard curve for quantification of HCMV by PCR was established and detective results of quality control templets were presented. The external standard method and the electrophoresis separation effect were appraised. The results showed that the method could be used for relative quantification of HCMV.

Restricted access

Abstract  

The National Institute of Standards and Technology (NIST) seaweed Standard Reference Material (SRM4359) was developed through an intercomparison of 24 experienced laboratories. Several statistical techniques were evaluated for establishing reference values using the laboratories’ reported values including mean, midmean, median, Type B On Bias (BOB), Graybill-Deal, Mandel-Paule, Vangel-Rukhin, Cox and Maximum Likelihood. After reviewing the results from all these techniques, the median was chosen as a suitably robust way to calculate reference values. The uncertainties for the median values were estimated using bootstrap analysis.

Restricted access

Abstract  

A UK primary standard and monitor calibration service for positron emitting radionuclides in gases are needed by users of cyclotron facilities to enable them to calibrate radioactivity-in-air monitors and thus ensure the accuracy and traceability of measurements of any airborne radioactivity releases arising from the production of these radionuclides. A system of gas flow proportional counters, already established at the National Physical Laboratory (NPL) for the standardization of β-emitting gases, was used as the basis of the primary standard. This paper focuses on initial problems encountered in the use of the system for measuring positron emitters.

Restricted access

Abstract  

Neutron activation analysis is one of many analytical techniques used at the National Institute of Standards and Technology (NIST) for the certification of NIST Standard Reference Materials (SRMs). NAA competes favorably with all other techniques because of it's unique capabilities for high accuracy even at very low concentrations for many elements. In this paper, instrumental and radiochemical NAA results are described for 25 elements in two new NIST SRMs, SRM 1515 (Apple Leaves) and SRM 1547 (Peach Leaves), and are compared to the certified values for 19 elements in these two new botanical reference materials.

Restricted access

Abstract  

The standard impact factor for particular fields of science (Ig) and the relative impact factor K for scientific journals are introduced. The technique of calculation of standard impact factor (Ig) for a field is an inherent part of a method which allows a cross-field evaluation of scientific journals. This method for evaluating scientific journals elaborated in 1988 was aimed at the analysis of Russian journals covered by the SCI database, it was also used for chemical journals (more that 300) and for journals in the Life sciences (more than 1000). The results are discussed.

Restricted access

Abstract  

In order to study effective applications of the photon activation analysis using the internal standard method, determinations of Cr, Co, Ni, Zn, As, Rb, Sr, Y, Zr, Nb, Sb, Cs, Ba, Ce and Pb in two marine sediments as environmental materials have been examined by the use of a personal computer-based gamma-ray spectrometer equipped with a micro-robot for sample changing. In these determinations, some major and minor constituent elements in the samples were properly used as effective internal standards to check the roles with each other. As a result, it was demonstrated that accurate and precise determinations of the above 15 elements were achieved efficiently and favourably.

Restricted access