Search Results

You are looking at 1 - 4 of 4 items for

  • Author or Editor: I. Vallés x
  • All content x
Clear All Modify Search

Abstract  

The activity of -emitting radionuclides is usually measured by semiconductor detectors (surface barrier or ion implanted). Overlapping and composite bands are quite common problems depending on energy differences of the radionuclides and counting source preparation. The classical approach to activity quantification is based on peak integration and, when it is used, overlapping may be overcome by a detailed study of each case, whereas composite bands can not be completely resolved. Here, spectra of the -emitting plutonium isotopes, obtained by ion implanted semiconductor detectors, have been used to compare the classical approach with a multivariate calibration method (MVC-PLS). The study is performed at environmental activity levels (0–52 dpm). The relative errors obtained for239+240Pu activity determination, using either the classical or the MVC-PLS approach with replicates, are good enough to quantify isotopes at low level activities. The distribution of relative errors is asymmetric, with a positive component for 0–10.5 dpm subset, in the classical approach whereas it is more symmetric in the MVC-PLS method. The results show that the classical approach depends on peak overlap, whereas the MVC does not. As a whole, MVC is a more robust method than the classical approach. Composite bands were studied using the239Pu–240Pu mixture; the MVC approach did not allow individual quantification due to the lack of signal reproducibility. This instability does not affect the regular integration procedures but it is important in the deconvolution processes. The lack of reproducibility is related to the source preparation process.

Restricted access
Journal of Thermal Analysis and Calorimetry
Authors: V. Balek, L. Pérez-Maqueda, J. Poyato, Z. Černý, V. Ramírez-Valle, I. Buntseva, and J. Pérez-Rodríguez

Abstract  

The effect of grinding on thermal behavior of pyrophyllite and talc as commonly used ceramic clay minerals was investigated by DTA, TG, emanation thermal analysis (ETA), B.E.T. surface area (s.a.) measurements, X-ray diffraction (XRD) and scanning electron microscopy (SEM). A vibratory mill was used in this study, grinding time was 5 min. It was found that the grinding caused an increase in surface area and a grain size reduction of the samples. From TG and DTA results it followed that grinding caused a decrease of the temperature at which the structure bound OH groups released. The formation of high temperature phases was enhanced with the ground samples. For the ground talc sample the crystallization of non-crystalline phase into orthorhombic enstatite was observed in the range of 800°C. For ground pyrophyllite a certain agglomeration of grains was observed in the range above 950°C. Moreover, for both clays the ETA characterized a closing up of subsurface irregularities caused by grinding as a decrease of the emanation rate in the range 250–400°C. The comparison of thermal analysis results with the results of other methods made it possible to better understand the effect of grinding on the ceramic clays.

Restricted access
Journal of Radioanalytical and Nuclear Chemistry
Authors: I. Gonçalves, A. Ramalho, I. Gonçalves, J. Salgado, J. Pertusa, A. Irles, F. Mascarenhas, M. Castro, F. Valle, J. Rico, and V. Alcober

Abstract  

The goal of this work is to pursue the research activity in BNC and the installation of a therapy facility in the position presently occupied by the thermal column. With these objectives the experimental studies in mice and cells are continuing while improvements in the facilities are created or prepared. For this effect: (1) the installation of lead shield in the vertical access of the thermal column, which resulted in an enhancement of the Φth toD γ ratio, was performed, (2) the adaptation of a beam tube to deliver a dominantly thermal or epithermal beam in two possible beam openings is being done and (3) Monte Carlo calculations aiming at the optimization of the conditions for the therapy installation are in progress.

Restricted access
Journal of Thermal Analysis and Calorimetry
Authors: L. Pérez-Maqueda, V. Balek, J. Poyato, J. Šubrt, M. Beneŝ, V. Ramírez-Valle, I. Buntseva, I. Beckman, and J. Pérez-Rodríguez

Abstract  

Thermal behavior of talc samples (from locality Puebla de Lillo, Spain) were characterized by emanation thermal analysis (ETA), DTA and TG. The ETA, based on the measurement of radon release rate from samples, revealed a closing up of surface micro-cracks and annealing of microstructure irregularities of the talc samples on heating in the range 200–500°C. For ground talc sample a crystallization of non-crystalline phase formed by grinding, into orthorhombic enstatite was characterized as a decrease of radon mobility in the range 785–825°C and by a DTA exothermal effect with the maximum at 830°C. ETA results characterized the microstructure development of the talc samples on heating and served to evaluate their radon mobility and transport properties on heating and cooling. Transport properties of the talc samples were evaluated by using ETA experimental data measured during heating to 600 and 1300°C, respectively, and subsequent cooling to room temperature.

Restricted access