Biomedical subjects

J M Gómez-Ros

Publications and source records attributed to J M Gómez-Ros.

8 recordsLinked to original sources

PubMed2006

Simple methods to analyse thermoluminescence glow curves assuming arbitrary recombination-retrapping rates.

Numerical solutions of the differential equations system describing the transitions between energy levels can help in the understanding of the physical mechanisms governing thermoluminescence (TL) emission but they are not suitable for the analysis of complex experimental TL glow curves. On the other hand, simplified descriptions, as mixed or general order kinetics, require many additional assumptions that may limit the validity of the results or are mostly empirical. In this paper, the accuracy of such approximations has been evaluated for different retrapping-recombination ratios and it has been found that differences between the fitted and the simulated parameters arise from the simplification of the models because quasi-equilibrium condition seems to be valid in all the considered cases.

Algorithms↗

PubMed2006

Thermal stability of the thermoluminescence trap structure of bentonite.

This work reports about the thermal stability of the blue thermoluminescence (TL) of a well-characterised natural bentonite from Almeria (Spain). The main interest of this clay, mainly composed of montmorillonite, is because of its application in the field of high-level radioactive waste (HLW) repository in deep-lying rocks. As observed in other aluminosilicates, bentonite exhibits a very complex structure of the emission spectra based on a wide broad maximum peaked at approximately 265 degrees C that can be associated to physico-chemical processes such as dehydroxylation processes, consecutive breaking linking of bonds, formation of hydrolysed ions and redox reactions. The thermal stability tests performed at different temperatures confirm a continuum in the distribution of traps. Hence, the glow curve analysis methods commonly used for synthetic materials based on single discrete traps cannot be applied for this material and the kinetic parameters were fitted assuming an exponential distribution of trapped electrons.

Bentonite↗

PubMed2006

Evolution of the trapped charge distribution due to trap emptying processes in a natural aluminosilicate.

The evolution of the thermoluminescence glow curve of a natural Ca-Be rich aluminosilicate after annealing treatments at different temperatures has been studied in order to evaluate the changes in the trapped charge distribution. The glow curve consists of a single broad peak that continuously shifts toward higher temperatures when the sample is preheated up to increasing temperatures, thus indicating the presence of a continuous trap distribution. The glow curve fitting assuming different distribution functions shows how a gaussian distribution becomes a nearly exponential distribution owing to the thermal leakage of charge carriers from trapping centres.

Aluminum Silicates↗

PubMed2004

A method for calculation of dose per unit concentration values for aquatic biota.

A dose per unit concentration database has been generated for application to ecosystem assessments within the FASSET framework. Organisms are represented by ellipsoids of appropriate dimensions, and the proportion of radiation absorbed within the organisms is calculated using a numerical method implemented in a series of spreadsheet-based programs. Energy-dependent absorbed fraction functions have been derived for calculating the total dose per unit concentration of radionuclides present in biota or in the media they inhabit. All radionuclides and reference organism dimensions defined within FASSET for marine and freshwater ecosystems are included. The methodology has been validated against more complex dosimetric models and compared with human dosimetry based on ICRP 72. Ecosystem assessments for aquatic biota within the FASSET framework can now be performed simply, once radionuclide concentrations in target organisms are known, either directly or indirectly by deduction from radionuclide concentrations in the surrounding medium.

Animals↗

PubMed2004

Absorbed dose rate conversion coefficients for reference terrestrial biota for external photon and internal exposures.

The paper describes dosimetric models that allow the estimation of average radiation exposures to terrestrial biota due to environmental sources in the soil as well as internal uniform distributions of radionuclides. Simple three-dimensional phantoms for 13 faunal reference organisms are specified. The calculation of absorbed dose per unit source strength for these targets is based on photon and electron transport simulations using the Monte Carlo method. The presented absorbed dose rate conversion coefficients are derived for terrestrial reference species. This allows the assessment of internal exposure as well as external photon exposure depending on the nuclide, habitat, target size and environmental contamination. To enable the application of specific radiation weighting factors for alpha-, low energy beta- (E0 < 10 keV), beta- and gamma-radiations, their partial contributions to the total absorbed dose are provided separately. The coefficients for external exposure are listed for organisms living above the ground for an infinite plane source 3 mm deep in soil, as well as for a horizontally infinite volume source uniformly distributed to a depth of 10 cm. Furthermore, the coefficients are also presented for organisms living in a contaminated 50 cm thick soil layer. A multi-layer canopy model for plants is also described. The conversion coefficients are given for 3H, 14C, 40K, 36Cl, 59,63Ni, 89,90Sr, 94Nb, 99Tc, 106Ru, 129,131I, 134,135,137Cs, 210Po, 210Pb, 226Ra, 227,228,230,231,232,234Th, 234,235,238U, 238,239,240,241Pu, 241Am, 237Np and 242,243,244Cm, together with their

Animals↗

PubMed2004

Estimation of internal and external exposures of terrestrial reference organisms to natural radionuclides in the environment.

In this paper, an estimation of the doses absorbed by terrestrial reference organisms due to naturally occurring radionuclides is described. For terrestrial organisms under normal circumstances, external exposure is estimated to be of the order of 0.1-0.4 mGy a(-1), depending on size and habitat, and the main contributor is 40K. Internal background exposures of terrestrial organisms are more variable. Again, 40K is an important contributor giving doses of the order of 0.3 mGy a(-1). The exposures of muscles and plant tissues to uranium, thorium, radium, lead and polonium are lower, but liver, bone and kidney may be exposed at levels of 0.1-1 mGy a(-1) absorbed dose. There can also be significant increases in the received dose under specific environmental conditions as is the case for burrowing mammals that receive relatively high lung doses due to the inhalation of radon and its progeny.

Animals↗

PubMed2002

Kinetic parameters of lithium and aluminium doped quartz from thermoluminescence glow curves.

The thermoluminescence (TL) glow curves of irradiated annealed and non-annealed synthetic beta-quartz (Li0.73Al0.73Si1.27O4) synthesised using the ceramic method have been studied. Annealed samples (1200 degrees C for 12 h) exhibit some changes of shape and intensity in the TL glow curves when compared to non-annealed samples in the range of 0.1-5 Gy. These changes can be attributed mainly to thermal alkali self-diffusion through the lattice interfaces involving modifications in the components of the luminescent traps. In non-annealed samples six groups of components at about 100 degrees C, 130 degrees C, 160 degrees C, 210 degrees C, 330 degrees C and 450 degrees C can be found, whereas annealed samples only display one very intense peak at a lower temperature (deconvoluted into three peaks at 90 degrees C, 105 degrees C and 130 degrees C) and a lower intensity second wide broad emission at approximately 240 degrees C. In this paper, a computerised curve-fitting based on general order kinetics has been used to characterise the glow curve structure resolving trapping parameters for each glow peak: trap depth (E), frequency factor (s) and the order of the kinetics (b). The dose dependence of the individual components of the glow curve has been also studied. These data allow us to select the most stable component for use in dosimetric purposes.

Aluminum↗

PubMed2002

Study of real heating profiles in routine TLD readout: influences of temperature lags and non-linearities in the heating profiles on the glow curve shape.

This paper reports on the results of a heating profile analysis using a commercial routine read-out system with non-contact hot nitrogen heating, using linear heating gas profiles. Glow curves of TLD-100 were analysed for different linear heating gas rates from 1 degree C x s(-1) to 30 degrees C x s(-1). The analysis of the individual peak maxima (Peak 2-5) leads to an approximation of the real heating profile in the TL detector. It was found that the real heating profile deviates strongly from linearity, and that the temperature lag between the heating gas and the detector reaches values up to some tens of degrees C. The consequences of this non-linearity, with respect to the resulting glow curves, are discussed in this paper. These results lead to a better understanding of the shape of routine TL glow curves and help to improve the use of glow curves analysis in routine services. In addition, a simple procedure is described which allows calculation of the real heating profile based on the heating gas temperature profile. This model shows a very good match between experimental data and calculated values.

Hot Temperature↗