G. Espinosa

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.

A new possibility for high-resolution spectroscopy of nuclear particles entering CR-39 at selected dip angles

Abstract In nuclear reaction studies a differentiation of the reaction products according to their type and energy is generally required. At right angle of incidence a particle identification method based on the relation netween the track diameter and particle energy can be well applied to plastic track detectors of low registration sensitivity. We have tried to extend this “track-diameter method” to the high-sensitivity CR-39 sheets by selecting special incident angles for particle detection. The utility of such a measuring procedure, called “track-size method”, is presented for alpha and proton spectroscopy. A theory is developed to calculate at arbitrary angles the main parameters affecting the energy resolving power of the “track-size method”, namely the critical layer thickness (which has to be removed from the detector surface for track-induction) and the depth and minor axis of etch-pits.

Digital imaging system for track measurements

Abstract A digital imaging system (DIS) has been implanted for counting and analysis of nuclear tracks in solids. This system presents advantages in comparison with similar systems. An optical microscope is used for the magnification of the tracks, a Color Camera Digital (CCD), converts the light into an electrical signal. Analog information is sent to the electronic card, digitizing the signal. In this case a Data Translation, Vision EZ ® card was chosen and the GLOBAL LAB ® image software was installed in the PC. The system has not only the capability foe automatic counting of track densities, as many other commercial and research systems, but also has the capability of track characterization, via the particle diameter determination. The system can digitize tracks from 4 to 100 μm in diameter, calibrating directly to the reference scale on the objective. Finally, the data measurements are handled by a calculus software for further analysis. The digital image analyzed is simple, easy to operate, and low cost compared with other systems.

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.

Different etching processes of damage track detectors for personnel neutron dosimetry

Abstract The advantages and limitations of different etching processes of CR-39 detectors for personnel neutron dosimetry are analysed. The chemical etching can be considered the converse of the electrochemical etching, since the former provides very poor response to low energy neutrons, while the latter greatly simplifies the registration of these neutrons. A foil of CR-39 etched electrochemically results in a simple and sensitive neutron dosimeter with a response proportional to the dose over the entire energy range of interest.

Angular distribution of fusion products and x rays emitted by a small dense plasma focus machine

Time integrated measurements of the angular distributions of fusion products and x rays in a small dense plasma focus machine are made inside the discharge chamber, using passive detectors. The machine is operated at 37kV with a stored energy of 4.8kJ and a deuterium filling pressure of 2.75torr. Distributions of protons and neutrons are measured with CR-39 Lantrack® nuclear track detectors, on 1.8×0.9cm2 chips, 500μm thick. A set of detectors was placed on a semicircular Teflon® holder, 13cm away from the plasma column, and covered with 15μm Al filters, thus eliminating tritium and helium-3 ions, but not protons and neutrons. A second set was placed on the opposite side of the holder, eliminating protons. The angular distribution of x rays is also studied within the chamber with TLD-200 dosimeters. While the neutron angular distributions can be fitted by Gaussian curves mounted on constant pedestals and the proton distributions are strongly peaked, falling rapidly after ±40°, the x-ray distributions show...

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 commercial bacterial colony counter for semiautomatic track counting

Abstract The information one must obtain from a solid state track detector depends on the specific application. The most common information need is the measurement of track density. The number of tracks per unit area is commonly used in neutron and alpha dosimetry, for example, to determine radiation dose. In recent years, a class of semi-automatic counting systems has become available for under