D. Palacios

Environmental radioactivity near the central coast of Venezuela and its radiological impact

The concentrations of40K,226Ra,232Th and137Cs were determined in the upper layers of soils in the central coastal region of Venezuela. The activities of137Cs are higher in the areas where the forest is well developed, oriented towards the wind and at higher elevations. The origin of the137Cs deposition is from water input from the clouds directly in the cloudforest and rainfall from the northeast trade winds. Even though the values of137Cs are much higher in these areas, there is little or no significant increase in the health risk. The natural radioactivity is correlated with the geology in the region except in the area of Urama. The values for the natural radiation background are as follows: for potassium between 1–3%, for radium between 1–3 ppm and for thorium the range was 6–39 ppm. The corresponding amounts of absorbed dose rates in air, the exposure rates and the annual effective dose equivalents are in the following ranges respectively: 11–39 pGy/s, 4–16 uR/h and 0.25–0.86 mSv/y. The annual effective dose equivalents include the contribution of the global average (2.57 mSv/y) of the rest of the natural sources of radiation. Finally, the largest natural radioactivity background, was found near Chichiriviche as a result of the massive granite deposits in this area, but again there is no significant health risk.

A new method to measure track density and to differentiate nuclear tracks in CR-39 detectors

Abstract An alternative method to count and differentiate nuclear tracks in SSNTD is described. The method is based on the analysis of Fraunhofer diffraction pattern of coherent light produced by tracks of an etched SSNT detector. The diffraction pattern was also simulated by applying computational Fourier Optics. The comparison between results obtained by simulation and by the theoretical model gave satisfactory concordance. The proposed method is capable of differentiating tracks in CR-39 by their diameter and energies. The diameter resolution ranged between 8% and 25%, while the counting error was less than 15%. The discriminating ability to distinguish genuine etched tracks from defects and background anomalies is demonstrated. The incidence angle did not influence significantly the total count and the track parameter measuring capability. Errors due to track overlapping are only significant for track densities higher than 3×10 5 cm −2 .

Neutron Activation Analysis of Pre-Columbian Pottery in Venezuela

Pre-Hispanic pottery figurines from north-central Venezuela islands and mainland were analysed by neutron activation analysis (INAA and PGAA) at the Budapest Research to establish their provenience. In order to classify the samples of figurines, characteristic molecular and atomic components were determined. Several mass ratios were calculated for significant classification of the object of two origins. Results shed light on the origin of island figurines and suggest specific areas of their production on the mainland, contributing to better understanding of late pre-Hispanic migration patterns in the southeastern Caribbean region.

Target and PADC Track Detectors for Rare Isotope Studies

A higher yield of rare isotope production methods, for example, isotope separation on-line (ISOL), is expected to be developed for the EURISOL facility. In this paper as a part of the ongoing project, high power-target assembly and passive detector inclusion are given. Theoretical calculations of several configurations were done using Monte Carlo code FLUKA aimed to produce 1015 fiss/s on LEU-Cx target. The proposed radioactive ion beam (RIB) production relies on a high-power (4 MW) multibody target; a complete target design is given. Additionally we explore the possibility to employ PADC passive detector as a complementary system for RIB characterization, since these already demonstrated their importance in nuclear interactions phenomenology. In fact, information and recording rare and complex reaction product or short-lived isotope detection is obtained in an integral form through latent track formation. Some technical details on track formation and PADC detector etching conditions complete this study.

Quality Control of Pavements and Tarmacs Using (137Cs) γ Compton Scattering

The γ Compton scattering over a volume of concrete has been studied in order to design an instrument for density measurements. It will be used for the quality control in road construction, where large surfaces must be monitored. The experimental results and Monte Carlo simulations of the γ Compton scattering over homogeneous and inhomogeneous volumes of concrete are shown. MC simulations have been useful to optimize the values of several parameters to improve the experimental set up and to estimate the extension of the explored volume.

New approach to determine the incident alpha energy and angle from track parameters

We propose two methods for determining the energy and incident angle of registered alpha particles in LR-115 detectors. One of them is based on geometric parameters of track openings at detector surface and the other on geometric parameters of projected tracks on detector surface. Track parameters were extracted from tracks simulated with the TRACK_TEST program. The incident energy and angle was estimated by interpolation and successive approximations in the databases of track parameters. The uncertainties in the calculated values were lower than 3% for both approaches.

On the Equivalent Sources and Geometric Factor Calculation for a Circular Detection Case

In all absolute measurements of the intensity of the radioactive materials and calibration of the detectors, it is essential the knowledge of the geometric efficiency. This work describes how to obtain the sources with different geometries and equal geometric efficiency (equivalent sources for geometric factor), corresponding to a linear, circumferential and circular homogeneous sources parallel to a circular detector. It is estimated the geometric factor of them by the Monte Carlo method. The results are compared with the published in the literature, thus confirming the validity of this method.

SSNTD Techniques in Radon Surveys for Hydrocarbon Exploration and Occurrence of Natural Gas Seeps

Leakages of hydrocarbon reservoirs often increase the radon concentration on the soil surface through distinct pathways; gas migration results in either prolific macro-seeps or micro-seeps. Soil gases, including radon, are recognized as potential tracers in geoscience. The surficial radiometric anomalies over hydrocarbon reservoirs provide the oil community with a complementary survey tool for oil exploration through the use of nuclear track methodology. The Solid State Nuclear Track Detector (SSNTD) is one of the recognized techniques to be employed advantageously in radon surveys for hydrocarbon exploration and occurrence of natural gas seeps. The nuclear track method provides information on the nature of radioactive gas sources, emanations from the soil and their transport pathways. Latent track etching conditions and their analysis are included.

Alternative Reconstruction Method and Object Analysis in Digital Holographic Microscopy

Holography is a method for storing and reconstructing both amplitude and phase information of a wave front. In digital holography the reconstruction process is accomplished by means of a computer (Yaroslavsky & Merzyalov, 1980) obtaining directly the phase distribution of the object wave front. Particularly with the improvement of the spatial resolution of CCD cameras and the increasing computational performance of personal computers digital holography has been widely applied in many fields such as deformation analysis (Schedin et al., 2001), object contouring (Wagner et al., 2000), microscopy (Takaki & Ohzu, 1999) and particle measurement (Murata & Yasuda, 2000). The technique of digital holography has been implemented in a configuration of an optical microscope (Schilling et al., 1997); the objective lens produces a magnified image of the object and the interference between this image and the reference beam is achieved by the integration of the microscope into one of the arms of a Mach-Zender interferometer. This configuration is called Digital Holographic Microscopy (DHM). DHM is a powerful technique for real-time quantitative phase contrast imaging, since a single intensity image, called a hologram, allows the reconstruction of the phase shift induced by a specimen. This property of holograms offers phase-contrast techniques, which can then be used for quantitative 3D imaging (Palacios et al., 2005). Quantitative phase imaging is important because it allows the determination of the optical thickness profile of a transparent object with sub-wavelength accuracy (Yu et al., 2009). Through numerical processing of the hologram one can filter out parasitic interferences and the components of the image reconstruction: zero-order and twin image terms (Cuche et al., 2000) or to compensate for curvature introduced by the microscope objective (MO) (Pedrini et al., 2001),

k0‐INAA of Archaeological and Industrial Venezuelan Samples

Archaeological and industrial Venezuelan samples were analyzed by k0‐INAA to provide new data on the provenance study of the figurines found in Los Roques Archipelago and on recycling of industrial by‐products. Los Roques and Valencia Lake Basin figurines are similar. Bottom Oil Ashes have 10 times the concentration of V, Mg, Ni, Fe, Na compared to ICP‐AES and TXRF results. Red Mud samples have Thnat and Unat from four to ten times higher concentrations than those recommended for building materials.