The possibility of using 14 MeV neutron activation for rapid, nondestructive elemental analysis of high Tc superconductors is considered. A method was elaborated and applied for investigating Y–Ba–Cu–O samples with different oxygen content. Derived from the measurements of a typical sample the uncertainty of the elemental concentrations, including oxygen, is not more than 1. 1%.
The validity of the Poisson and theP(k) modified Poisson statistical density functions of observing k events in a short time interval t=T/n, proposed previously by others, is investigated experimentally in radioactive decay detection for various measuring times, T. The experiments to measure radioactive decay were performed with 89my (T1/2=16.06 s), using a multichannel analyzer operating in the multiscaling mode. According to the results, Poisson statistics adequately describes the counting experiment for short measuring times (up to T<0.5 T1/2) and its application is recommended. However, analysis of the data demonstrated, with confidence, that for long measurements (T>1 T1/2) Poisson distribution is not valid and the modified Poisson function is preferable.
Fast neutron activation analysis experiments were performed to investigate the analytical possibilities and prospective utilization of short-lived activation products. A rapid pneumatic transfer system for use with neutron generators has been installed and applied for detecting radionuclides with a half-life from 300 ms to 20 s. The transport time for samples of total mass of 1–4 g is between 130 and 160 ms for pressurized air of 0.1–0.4 MPa. The reproducibility of transport times is less than 2%. The employed method of correcting time-dependent counting losses is based on the virtual pulse generator principle. The measuring equipment consists of CAMAC modules and a special gating circuit. Typical time distributions of counting losses are presented. The same 14 elements were studied by the conventional activation method (single irradiation and single counting) by both a typical pneumatic transport system (run time 3 s) and the fast pneumatic transport facility. Furthermore, the influence of the cyclic activation technique on the elemental sensitivities was investigated.
A CAMAC system was installed for pulse height analysis and correction of counting losses due to the dead-time of a multichannel analyzer and the pulse pile-up. A computer program was developed to control the whole system, and to collect and store data in both conventional and cyclic measurement modes.
An activation analytical method has been developed for determining Cd, Ag, Sb, Se, Br by 14 MeV neutron-induced X-ray emission spectroscopy using Pr as an internal standard. A good correlation was obtained between the activity ratio, RAo and the weight ratio, RW. Results are given after correction for self-absorption and without correction. The results are comparable in both cases when dilution with H3BO3 (90%) is applied. The elements listed can be determined at minor concentrations (0.01%) with a relative error not more than ±5%.
The empirical coefficient method represents the absorption and enhancement effect of each element on each other by parameters independent of mass concentrations. This method is used together with the internal standard method for the determination of cadmium, bromine and selenium by 14 MeV neutron activation followed by X-ray spectrometry. The results of analysis show a relative error not more than ±5%.
The problem of converting measured intensities into mass concentrations arises from the fact that the measured intensity of a characteristic X-ray line of an element or compound depends not only on the mass concentration of that element or compound but also on the nature and abundance of the other constituents of the specimen. In this work the empirical coefficient method which comprises both absorption and enhancement effects of each element on each other element by parameters independent of mass concentrations was used for correction of enhancement effects from antimony and praseodymium on bromine in two groups of samples. The results of analysis of bromine shows a relative error of not more than ±4%.
14 MeV neutron activation followed by X-ray spectrometry was applied to the simultaneous nondestructive determination of cadmium, antimony and bromine, utilizing praseodymium as an internal standard. The results of analysis show a relative error not higher than ±5%, when the samples were diluted with H3BO3
-5% to minimize the interelement effects.
The intensity of characteristic X-rays emitted from one element may be reduced by partial absorption by other elements in the matrix, or alternatively it is enhanced by their presence. In this work the enhancement effect of antimony on bromine, cadmium and selenium are given. The dependence of the specific activity of each element /Cd, Br and Se/ on the ratio of the weight of Sb to that of the element is given, when the concentration of Sb is not very low /-5%/.