J.I. Golzarri

Isotropic and anisotropic components of neutron emissions at the FN-II and PACO dense plasma focus devices

The average angular distribution of neutron emissions has been measured in the Fuego Nuevo II (FN-II) dense plasma focus device (5 kJ) by means of CR-39 plastic nuclear track detectors. When pure deuterium is used as the filling gas, the data can be adjusted to a Gaussian function, related to anisotropic emission, superposed on a constant pedestal, related to isotropic emission. When deuterium–argon admixtures are used, the anisotropic contribution is best represented by a parabola. The same analysis is applied to previously reported results, for fewer shots, in pure deuterium from the PACO device, which is similar in size to the FN-II. In both devices the anisotropic component is smaller than the isotropic one, but with different features. In PACO the anisotropic component is concentrated on a large narrow beam around the axis, but its contribution to the total neutron yield is significantly smaller than in the FN-II, where the anisotropic component spreads over a wider range. The neutron flux per shot is monitored in both devices with calibrated silver activation detectors, at 20° and at 90° from the axis. The average values of the neutron flux at these two angles are used, along with the angular distributions obtained form the track detectors, in order to estimate the absolute neutron yield of both the isotropic and the anisotropic contributions. From examining different groups of shots, it is found that the shape of the angular distribution is important in the estimation of anisotropy, and that the value usually reported, as the ratio of neutron counts head-on and side-on, as measured by activation counters, may be misleading.

Neutron anisotropy and X-ray production of the FN-II dense plasma focus device

The FN-II Dense Plasma Focus is a small (< 5kJ ) Mather type device, where the dependence of neutron yield and its anisotropy, in terms of deuterium filling pressure, and the neutron emission angular distribution have been studied. Two diferent electrode configurations have been tested, showing that their geometry plays an important role both on neutron yield and anisotropy. Time integrated anisotropy has been measured with silver activation counters, on a shot to shot basis. CR-39 nuclear track detectors are used to determine the angular distribution of neutrons, averaged over tens of shots, showing that an isotropic pedestal accounts for 70% of the emission, while the anisotropy component accounts for the remaining 30%. The neutron yield shows a tendency to increase with anisotropy, as well as with the emission of hard X-rays observed on-axis. Scintillator- photomultiplier detectors show a slight Doppler shift in the neutron energy at backward angles, supporting the beam-target mechanism. Additional information has been obtained from time inte- grated X-ray diagnostics, which include filtered multi-pin-hole cameras.

Indoor radon measurements and methodologies in Latin American countries

According to the current international guidelines concerning environmental problems, it is necessary to evaluate and to know the indoor radon levels, specially since most of the natural radiation dose to man comes from radon gas and its progeny. Several countries have established National Institutions and National Programs for the study of radon and its connection with lung cancer risk and public health. The aim of this work is to present the indoor radon measurements and the detection methods used for different regions of Latin America (LA) in countries such as Argentina, Brazil, Ecuador, Mexico, Peru and Venezuela. This study shows that the passive radon devices based on alpha particle nuclear track methodology (NTM) is one of the more generalized methods in LA for long term indoor radon measurements, CR-39, LR-115 and Makrofol being the more commonly used detector materials. The participating institutions and the radon level measurements in the different countries are presented in this contribution.

Distribution of indoor radon levels in mexico

Abstract Our laboratory has carried out a systematic monitoring and evaluation of indoor radon concentration levels in Mexico for ten years. The results of the distribution of indoor radon levels for practically the entire country are presented, together with information on geological characteristics, population density, socioeconomic levels of the population, and architectural styles of housing. The measurements of the radon levels were made using the passive method of nuclear tracks in solids with the end-cup system. CR-39 was used as the detector material in combination with a one-step chemical etching procedure and an automatic digital-image counting system. Wherever a high level was measured, a confirming measurement was made using a dynamic method. The results are important for future health studies, including the eventual establishment of patterns for indoor radon concentration, as it has been done in the USA and Europe.

The atomic force microscope as a fine tool for nuclear track studies

Atomic force microscopy (AFM) is a relatively new tool in the study of materials used in the nuclear track methodology. The sensitivity to detect ionizing nuclear particles is strongly influenced by the surface roughness of the material used as detector. In this contribution a surface analysis of several commercial polycarbonates used as nuclear track detectors is presented.

A Monte Carlo study of radon detection in cylindrical diffusion chambers

The functioning of radon diffusion chambers was studied using the Monte Carlo code RAMMX developed here. The alpha particles from radon are assumed randomly produced in the volume of the cylinder, and those from the progeny are assumed to originate randomly at the cylindrical surface. The energy spectrum, the distribution of incident angles, and the distribution of path lengths of the alpha particles on the detector were obtained. These quantities vary depending on input parameters such as initial alpha particle energy, radius and depth of the diffusion chamber, detector size and atmospheric pressure. The calculated energy spectrum for both (222)Rn and (220)Rn was compared with experiment, permitting the identification of each peak and its origin, and a better understanding of radon monitoring. Three aspects not considered in previous calculations are progeny alphas coming from surfaces of the monitor, taking into account the atmospheric pressure, and including the isotope (220)Rn.

Radon measurements of groundwater in Mexico

Abstract Radon measurement has important applications in hydrogeological studies (Fukui, 1985). Specifically, radon measurement is used to determine the fluctuations of the piezometric levels in groundwater and, in some cases, the path of the water, which is one of the key parameters to evaluate hydrogeological resources. Water from springs and deep wells in the Basin of Mexico and the valley of San Luis Potosi were sampled, measured and analyzed (Cortes and Jaimes, 1990). In this work a method for measuring 222 Rn in groundwater by using a passive detector is presented and the results are compared with a similar experiment performed at the same time, using the dynamical method. The aim of the work is to develop a method for detecting, evaluating and measuring the 222 Rn in groundwater by using SSNTD technology (Espinosa et al , 1981; Varhegyi et al , 1988).

Natural radioactivity in Mexican building material by SSNTD

Abstract The measurement and evaluation of natural radiation in building materials is a topic of current interest, due to the fact that it amounts to 40% of the total contribution of radiation to the general population. In this paper several commercial building materials commonly used in houses and buildings in Mexico are analyzed, determining their contents of Uranium and Thorium and their daughters by the nuclear track method. A CR-39 detector is used with chemical and electrochemical developing processes under standard conditions. Finally, the results are compared with those of building materials reported in other countries.

Measurement of nanosize etched pits in SiO2 optical fiber conduit using AFM

Abstract Fission fragment tracks from 252 Cf have been observed in SiO2 optical fiber, using an atomic force microscope (AFM), after a very short chemical etching in hydrofluoric acid solution at normal temperature. The nuclear track starting and evolution process is followed by the AFM direct measurements on the material surface and beyond a fine layer of the surface material. The images of the scanned cones were determined observing the two predominant energies from 252 Cf fission fragments and the development of the tracks in the 150 μm diameter optical fiber conduit.

Permeability of some materials to radon

Abstract Radon is a noble gas capable of permeating microscopic imperfections such as crevices, pores and structural failures in materials (Cothern and Smith, 1987; Culot et al, 1976). This represents a serious problem if a control of the radon levels between the soil and the basements of buildings, is to be achieved by intervening radium impervious barrier. In order to understand the behavior of radon in this respect, we have measured the relative radon permeability of a number of materials: polyethylene of differents thicknesses, various paper materials, aluminum foils and mylar using solid state nuclear track detectors. The results of our experiments provide some insight into the required properties for the better barrier materials for controlling the indoor levels of radon.