Search Results

You are looking at 1 - 10 of 72 items for

  • Author or Editor: A. Sánchez x
  • Refine by Access: All Content x
Clear All Modify Search

Abstract  

A method is described incorporating the procedures used in the radiochemical assay of Pu, Am and radiostrontium in environmental samples into a single radioanalytical sequential scheme. Sequential schemes have been used for determining the transuranic nuclides (isotopes of Pu and Am) in various types of sample matrices, but do not normally incorporate90Sr within the same scheme. The method offers potential savings in analyst time and reagents for the analyses of these nuclides, and is particularly suitable for small analytical laboratories where manpower resources coupled with a limited working time (8-hour working day) are constraints, and where limited amounts of sample are submitted for the analyses of all 3 radionuclides.

Restricted access

Abstract  

The uranium concentration, and234U/238U and235U/238U activity ratios were measured by alpha spectrometry of surface water from the neighbourhood of the uranium mines El Lobo and El Pedregal (Badajoz, Spain) before and after the rainy season. Changes were observed in all the three parameters studied. Leaching and dilution are the probable mechanisms for the seasonal changes in the concentration and in the234U/238U activity ratio as measured in open and dynamic systems (rivers).

Restricted access

Thermal studies on metal complexes of 5-nitrosopyrimidine derivatives

VI. Thermal behaviour of Zn(II), Cd(II), Hg(II) and Hg(I) complexes of 4-amino-1,6-dihydro-2-methylthio-5-nitroso-6-oxopyrimidine

Journal of Thermal Analysis and Calorimetry
Authors: M. P. Sánchez -Sánchez, J. M. Salas -Peregrín, M. A. Romero -Molina, and J. Ruiz Sánchez

The following Zn(II), Cd(II), Hg(II) and Hg(I) complexes of 4-amino-1,6-dihydro-2-methylthio-5-nitroso-6-oxopyrimidine (MTH) have been prepared and their thermal behaviour studied by TG and DSC techniques: Zn(MT)2·3H2O, Cd(MT)·H2O. Cd(MTH)Cl2, Hg(MTH)Cl2 and Hg2(MT)(NO3). The dehydration and dehalogenation enthalpy values were calculated.

Restricted access

Abstract  

The use of a232U spike as a yield monitor of chemical and physical processes to prepare and measure natural uranium in environmental samples by alpha-spectrometry is discussed versus the use of other artificially made isotopes of uranium.

Restricted access

Abstract  

In the course of measurements of uranium contamination in rivers of the Guadiana basin we have found the logical contamination near the uranium mines and a234U/238U ratio near 1 in the neighbourhood of the sources. With distance we find not only the expected decreasing contamination but also higher values of the activity ratio234U/238U. This observation seems to contradict the usual explanation of preferential leaching of234U as origin of the general234U enrichment of ground water.

Restricted access

Abstract  

We have experience of two methods for the analysis of 14C in environmental samples and have used this experience to directly compare these two techniques. Nine vegetation samples and a sucrose standard were analyzed using the benzene synthesis and combustion techniques. The results obtained using both methods were in good agreement and show that 14C data obtained using either technique are comparable. The analytical requirements for the two techniques vary considerably. In choosing a technique, a variety of factors such as sensitivity, sample size, sample type, carbon content and how the results are to be expressed, need to be considered.

Restricted access

Abstract  

Some remarks are given comparing two recently published methods of electrodeposition of uranium on stainless steel planchets to prepare sources for -spectrometry. Parameters used in the two procedures are discussed, and a general method of determining the best electrodeposition yield is proposed.

Restricted access

Abstract  

Determination of very low-level activity in samples using -spectrometry is possible due to the low background. In order to determine the chemical yield in the separation of the element of interest, a spike must be added to the sample. In many practical cases there is no adequate spike or it is not available in the laboratory. In these cases a spike of the radionuclide already pesent in the sample can be used as the so-called inner standard method. In order to achieve the best results the optimal quantity and the spike to choose must be determined to reduce the uncertainties associated with the activities. The present work is a systematic study of these problems. These considerations were used to the determination of thorium in environmental samples.

Restricted access

Abstract  

A combination of solid phase extraction, coprecipitation, and neutron activation techniques has been used to develop a speciation analysis method based on green chemistry for the major arsenic species in drinking water. Arsenate as As(V), monomethylarsonic acid (MMA), and dimethylarsinic acid (DMA) are separated and preconcentrated by strongly anion and cation exchange columns in tandem while As(III) remains in the effluent. These species are then selectively eluted and As(III) coprecipitated with bismuth sulphide. This simple method has been applied to the analysis of water reference materials with good results. The detection limits are 0.9, 1.7, 1.6, 3.8 and 16 ng mL−1 for As(III), As(V), MMA, DMA and total arsenic, respectively, using a neutron flux of 2.5 × 1011 cm−2 s−1 at the Dalhousie University SLOWPOKE-2 reactor (DUSR) facility and anti-coincidence gamma-ray spectrometry.

Restricted access

Abstract  

The enrichment of234U in ground waters is a well established experiments fact. In the course of measurements of uranium contamination in rivers of the Guadiana basin we have found the contamination near the uranium mines with the equilibrium isotope ratios of uranium. With distance from the mines we found not only the expected decrease in contamination but also an increasing enrichment of the lighter isotopes. For the235U isotope, this is the first observation with good separation and low interference between the most significant peaks of each isotope.

Restricted access