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  • Author or Editor: J. Op De Beeck x
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Abstract  

It is shown that activation analysis is especially suited to serve as a basis for determining the chemical similarity between samples defined by their trace element concentration patterns. The general problem of classification and identification is discussed. The nature of possible classification structures and their approriate clustering strategies is considered. A practical computer method is suggested and its application as well as the graphical representation of classification results are given. The possibility for classification using information theory is mentioned. Classification of chemical elements is discussed and practically realized after Hadamard transformation of the concerntration variation patterns in a series of samples.

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Abstract  

It is shown that the large sophisticated programs designed for big computers can be efficiently used on medium scale machines for complete quantitative neutron activation analysis with Ge(Li) detectors.

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Abstract  

The double irradiation technique, which is used to detect the production of a given nuclide from different chemical elements, by two different reactions in a polyenergetic neutron flux, cannot be generally applied. The application limits have been defined and calculated, based on the statistical fluctuation of the measured activities. The experimental verification and the practical applications of the calculated limits for activation analysis, and transmutation reaction cross section studies are discussed.

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Abstract  

Equations to calculate the second order reaction interferences in activation analysis have been derived. A simple approximation as well as the exact solution have been investigated. A new algorithm is proposed for fast and accurate calculations, without the need of a computer with high precision arithmetic. The method can be used for all higher order reaction chains.

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Abstract  

A comparison has been made between flux density distributions from massive and ring-shaped cylindrical isotopic neutron sources. A considerable gain in direct fast neutron flux is obtained for the latter geometry as well as a neat separation of fast and thermal flux density maxima along the axis of the source. Applications of these favourable properties are discussed.

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Abstract  

A Compton suppression gamma-ray spectrometry system has been evaluated for its use as a low level radioactivity counting facility. The system consists of a premium quality Ge(Li) detector surrounded by a shield of NaI(T1) detector material. Compton suppression is obtained by operating the two detector systems in anti-coincidence. Spectrum collection hardware consists of a NP11-A (DEC) interface for two ADC's and a PDP 11/T 10 minicomputer with 64 K byte core memory. Software development and system operation modes are described. System performance as a function of physical characteristics of the sample, scattering angle and gamma-photon energy, is discussed. Continum reduction for cascaded gamma-transitions and natural backgorund are considered separately.

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Abstract  

A non-destructive method has been developed for the precise and accurate determination of Sn in cassiterite ores. Irradiation is performed by means of a 6.6 Ci227Ac−BE isotopic neutron source with a total neutron output of 108 n·sec−1. Samples are pellets pressed from a mixture of cassiterite powder and wax as a binding material. With a 4 hrs analysis time and a relative precision of 0.45%, the new method is faster and at least as precise as any existing destructive chemical method. The accuracy is proved to be better than that of the commonly used iodimetric titration method.

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Abstract  

A method has been developed to routinely analyse managanese ores and ferro-manganese, by neutron activation making use of a cylindrical 1 Ci226Ra−Be source. A description of the source, the moderator and the pneumatic irradiation facility is given. The irradiation position has been optimized for minimum flux gradients and maximum reproducibility. Samples and standards consist of pellets pressed from a mixture of powdered material and graphite weighing approximately 5 g. Samples and standards alternatively go through a sequence of 20 min irradiation, 20 min decay, and 20 min counting. Pyrolusites containing from 30 to 55% Mn and ferro-manganese containing approximately 80% Mn have been analysed with a precision of 0.1% absolute.

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