Search Results

You are looking at 101 - 110 of 7,326 items for :

  • All content x
Clear All

Abstract  

Because of the demand for higher sensitivity radionuclide measurements,atom counting technology will become an increasingly used modality in geo-and bio-studies, and process control operations. It is anticipated that requestsfor standards, intercomparisons and performance evaluations services willsurge in the near future. In anticipation of such requests, the state-of-the-artneeded to be assessed for proactive planning purposes. The results of a workshopfocused on these issues indicated that there are several ongoing standards,intercomparisons and performance evaluations thrusts which are expected toexpand in the future. Furthermore, new projects were planned and the Councilon Ionizing Radiation Measurements and Standards (Public and EnvironmentalRadiation Protection subcommittee) was proposed as an information coordinator.

Restricted access

Abstract  

Three proposed National Bureau of Standards clay standard reference materials, flint clay SRM 97b, plastic clay, SRM 98b, and brick, SRM 679 were investigated for homogeneity with respect to their contents of Sm, La, Sc, Th, Hf, As, Ga, Fe and Cr. Sub-samples were analyzed by instrumental neutron activation analysis (INAA) and replicate determinations were made on nominal sample weights of 100, 400, 750, and 1000 g. For Sm, La, Sc and Th, no increase in the relative standard deviation with decreasing sample weight was observed in all SRMs indicating that subsampling error for these elements was not a large component of the overall error. For Ga in all SRMs and Cr, As and Fe in SRM 98b, an increase in the relative standard deviation with decreasing sample weight suggests that these elements are concentrated in a minor component of the sample. The three clays should be good reference materials for trace element microanalysis for the elements investigated.

Restricted access

Abstract  

Neutron activation analysis (NAA) is used extensively at the National Bureau of Standards as one of the analytical techniques in the certification of Standard Reference Materials (SRMs). Characteristics of NAA which make it valuable in this role are: accuracy; multielemental capability; ability to assess homogeneity; high sensitivity for many elements, and essentially blank-free nature. Examples of recent SRM analyses illustrating these characteristics are described.

Restricted access

Abstract  

A routine procedure for monostandard INAA using short-lived radionuclides with half-lives from 2 min to 15 hrs is described. Ten elements (Al, Mg, Ti, V, Mn, Cl, Na, K. Br and Cu) are determined in Chinese Biological Standard Reference Material (peach leaves). The quality of analysis was checked by analyzing the U. S. NBS Standard Reference Materials SRM-1571 and SRM-1648.

Restricted access

Résumé  

Une technique non destructive est exposée permettant le dosage d'environ 20 éléments minéraux dans des particules atmosphériques collectées sur filtre. Sur l'échantillon inconnu on dépose une quantité connue de rubidium qui sert de standard interne. L'échantillon inconnu et l'échantillon de référence sont irradiés dans les mêmes conditions pendant plusieurs jours dans un flux de neutrons thermiques, puis comptés sur détecteur Ge(Li). Les avantages et les limitations de la technique du standard interne sont discutés.

Restricted access

Abstract  

The monostandard method with the use of Ge(Li) γ-spectrometry has been elaborated with a critical evaluation of the nuclear data involved in activation and activity measurement. The method was tested by analysing simultaneously 15 elements in a well known standard material of Kale powder and 12 elements in NBS standard glass samples. The results are compared with the reported data to prove the accuracy of the monostandard method.

Restricted access

Summary  

In order to calibrate vials containing charcoal for measurement of radon, emanation sources of radon were produced in-house using 226Ra salts. Calibrated emanation standards containing solution of 226Ra(NO3)2 absorbed into inorganic compounds were prepared. The emanation coefficient of 222Rn for these standards vary from 0.23-0.25. The emanation sources were found to be suitable for calibrating radon monitors.

Restricted access

Abstract  

One of the more difficult problems associated with comparative neutron activation analysis (CNAA) is the preparation of standards which are tailor-made to the desired irradiation and counting conditions. Frequently, there simply is not a suitable standard available commercially, or the resulting gamma spectrum is convoluted with interferences. In a recent soil analysis project, the need arose for standards which contained about 35 elements. In response, a computer spreadsheet was developed to calculate the appropriate amount of each element so that the resulting gamma spectrum is relatively free of interferences. Incorporated in the program are options for calculating all of the irradiation and counting parameters including activity produced, necessary flux/bombardment time, counting time, and appropriate source-to-detector distance. The result is multi-element standards for CNAA which have optimal concentrations. The program retains ease of use without sacrificing capability. In addition to optimized standard production, a novel soil homogenization technique was developed which is a low cost, highly efficient alternative to commercially available homogenization systems. Comparative neutron activation analysis for large scale projects has been made easier through these advancements. This paper contains details of the design and function of the NAA spreadsheet and innovative sample handling techniques.

Restricted access

This study aims to throw light on questions of 20th-century rural housing construction using standard plans with features differing from traditional architecture, and how this was related to lifestyle. Houses built to standard plans are significant not only from the architectural viewpoint but also as regards modernisation and the changing lifestyle. These houses are often the forerunners of modernisation and innovations, setting a pattern. The state projects in the interwar years were also responses to the deepening social crisis. The ONCSA (National Folk and Family Welfare Fund) movement was undoubtedly the most influential among the construction projects using standard plans in the interwar years, not only because of the numbers involved (more than 10,000 houses were built), but also because of the level of preparation and organisation.Construction with state support and using standard plans continued after the Second World War. A number of independent settlements were created in the early 1950s using these standard plans. Ebes was a typical example of this socialist village-building. From the 1960s there was a rapid proliferation of a new type of building, the square house that increasingly dominated the appearance of the village street and represented a complete departure from the earlier, traditional architectural forms and types. As a result of the new building types, modernisation and technical development, new objects and implements appeared in material culture, also influencing the lifestyle: it is sufficient to mention lighting, electrical appliances, mains water and modernised forms of heating.

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