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Abstract  

The position of pre-irradiation separations in neutron activation analysis is shortly discussed. Special attention is given to separations for purification and/or concentration of analyte elements, either complexed or uncomplexed, via sorption on activated carbon. It was shown for a number of trace elements that the blank value introduced due to the use of activated carbon is small or mostly even negligible. The NAA determination via pre-separations based on activated carbon is highlighted for selenium, cobalt and iodine.

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Abstract  

Neutron activation analysis of cobalt, selenium and iodine requires pre-concentration of traces when the best possible conditions of sensitivity and accuracy are required at short irradiation times. The reason is 60mCo, 77mSe and 128I present half-lives of 10.5 m, 17.5 s and 25 m, respectively, which do not allow neither to dissolve the sample nor to perform any radiochemical separation after irradiation. On the other hand, their emissions are located in the beginning of the spectrum (59, 161 and 441 keV, respectively) where the Compton continuum makes difficult the identification and measurement of the peaks. This paper describes how foodstuff samples are dissolved in pure HNO3 by using conventional pressure pumps at 120–140 °C during 3–4 hours. Once cooled down the acid solution, distilled water is added and pH fixed at 1–1.5 with ammonia. 20 mg of APDC are added while stirring during 2 minutes and the solution is passed through 50 mg of activated carbon, where the Se traces are trapped. Then the filtered solution is adjusted to pH 4–6 with ammonia and passed through a fresh identical activated carbon filter where the iodine traces are caught. Finally, to the filtered solution is added 20 mg of cupferron at same pH, stirring for 2 minutes and passed through a third identical carbon filter, where the cobalt traces remain. In this way, we have the cobalt, selenium and iodine traces in three different, extremely pure carbon matrices, with a small, known mass of cobalt, selenium and iodine as background. Each filter is ready to be irradiated during a suitable time, to calculate separately at maximum sensitivity and accuracy the concentration of these three trace elements so important to human nutrition.

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Abstract  

Nuclear chemistry is usually associated with great disasters, especially the atomic bomb; this without reflecting that knowledge of nuclear chemistry has also had many benefits in the field of medicine and health. Whereas in technologically advanced countries, nuclear chemistry is considered to be an important part of the syllabus, including topics such as radioactivity with the emphasis in making conscience in the common citizen of the inherent benefits.

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Abstract  

The retention of iodine traces (ppb) was investigated in small activated carbon filters (50 mg) from solution at a yielding rate exclusively determined by pH. Retention is approximately 100% at pH values of 4–6, while no retention of iodine traces occurs after filtering them through an activated carbon filter from very acidic and basic solutions (pH values of 1 and 11, respectively) with 0% yielding rate. Since activated carbon is a very pure material, this procedure may be an alternative method of the activation analysis of iodine traces in foodstuffs, because the half-life of 128I, formed by (n,g) reaction, is only 25 minutes. It does not allow either the sample to be placed readily in solution or the radioisotope to be separated after irradiation with the purpose of attaining maximal accuracy and sensitivity in this type of analysis.

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Abstract  

Mass Spectrometry has been the usual method to determine Ar concentrations in mineral samples for dating them through the40Ar/40K ratio. This technique has been replaced since 1966 by measurement of40Ar/39Ar ratio, after artificial production of39Ar from the39K(n,p)39Ar reaction produced in the fast neutron flux of a nuclear reactor. This method requires the fusion of the sample by incremental heating until reaching a temperature of 1000°C in order to get the total release of both argon isotopes. In principle, it should be possible to determine the40Ar/40K ratio by activation analysis in an easier, non-destructive way, but it presents the following drawbacks: manufacture of argon standards; usual low ratio peak/Compton distribution for both peaks: 1.29 Mev and 1.52 Mev (41Ar and42K respectively), since potassium minerals are usually very rich in sodium, manganese and chlorine; reaction41K(n,p)41Ar induced by fast neutrons present in the thermal flux; and possible contamination of the samples and standards with atmospheric40Ar (99.6% of elementary Ar, whose proportion in the atmosphere at sea level is 0.93%). This paper describes how these problems may be solved, also determining the limits of Ar and K concentration related to Compton distribution, in our experimental conditions.

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Abstract  

The classification of low and medium level radioactive wastes produced regularly by nuclear power plants is becoming ever more important in Mexico, after a few years of running the first of two units, 600 MeV each, in Laguna Verde nuclear power plant. This paper describes a method to separate and detect traces of the weak -emitter63Ni, which is one of the activation products used to classify low and medium level radioactive wastes originating from the operation of nuclear power plants.

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Summary  

Autoradiography of green leaves and flowers are presented, after absorption with three kinds of mineral ions: the very common one in nature Na+, the toxic CrO4 2- and the nutritional I-, labeled with 22Na, 51Cr and 131I respectively, in order to test directly how these ions are distributed in a different way throughout the vegetable tissues, depending whether they are associated or not to synthetic fulvic acids commercially produced as fertilizers in Mexico. Two kinds of Polaroid films have been used and the necessary exposition time for the activity used is one week as a minimum, since these tracers are gamma- and X-rays emitters and, therefore, their action on the film is much weaker than that obtained with beta particles. It has been verified the effect brought about by synthetic fulvic acids, as fertilizers which distribute more evenly mineral ions into vegetable tissues, when they form a complex [I-], but they act as discriminators in the case of toxic ions [CrO4 2-] or when they do not form a complex [Na+].

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Journal of Radioanalytical and Nuclear Chemistry
Authors:
O. Rizo
,
E. Herrera Peraza
,
M. Manso Guevara
,
I. Pellón
,
M. López Reyes
,
M. Cabrera
, and
M. Montero Cabrera

Abstract  

The main results obtained during the characterization of the Triga Mark III reactor at NNRI, Salazar, Mexico, the development of the nonconventional multimonitor HAV-1, the use of Certified Reference Material (CRM) as multimonitor fork 0-factors experimental determination, and to study the reactor power and slowing-down thickness dependencies of the reactor flux parameters and its influence ink 0-INAA are presented. The experience of thek 0-INAA group at ISCTN, in the application of this analytical technique for different purposes is resumed.

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Summary  

After the Chernobyl accident in April 1986, Mexico imported from one European country a shipment of 28,000 tons of milk powder contaminated with the fission product 137Cs. Since then, the local authorities of Public Health have established as a compulsory condition to obtain through gamma-spectroscopy a certificate of no radioactive contamination either to imported or exported foodstuffs. But at the same time, the absence of long-lived, gamma-emitters fission products is certified, it is also possible to find the concentration of the important trace element K in foodstuffs, by the peak of 1461 keV from 40K, invariably present in the gamma-spectra. Taking advantage of the fact that it does not require any previous manipulation of the sample, this paper describes the general procedure in milk powder or any other foodstuff.

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Abstract  

The method described in a previous work to separate trace amounts of selenium in organic samples without using a carrier, based on the adsorption on active carbon filters of the complex formed with ammonium pyrrolidindithiocarbamate (APDC) at pH 1.5–2, has been applied to urine samples from 15 females patients suffering from cervical uterine cancer. With this type of sample the method reaches a maximum sensitivity (few ppb) with a good statistical variation (±12%). Since the highest concentration of selenium in human tissues is found in the kidney, and the elimination of this element is mainly by the urine, the method seems to be a powerful tool in the research about the human metabolism of selenium. This paper shows a possible relation of selenium concentration in human urine and the evolution time of cervical uterine cancer, in spite of limits imposed by the statistical error plus the inhomogeneity of the sample.

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