R.B. Gammage

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.

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.

Indoor radon concentration survey in Mexico

Indoor radon evaluations in specific regions of the country have been performed in an effort to assess the magnitude of the radon problem and its public health consequences. The survey of this paper covers four large non-tropical regions of north and central Mexico, and reports the results of measurements of indoor radon concentrations in houses of towns with between 100,001 and 500,000 inhabitants. The measurements were done by using passive detectors, namely, the closed-end-cup system with CR-39 polycarbonate chips as detector material. The measurements were performed throughout the two coldest seasons (between 5 and 20°C), winter and spring, in integration periods of 28 days covering the six month cycle. The results show a moderate average radon concentration below 200 Bq·m−3 with occasional higher values. This is very probably due to the climate conditions and the traditional habits of open door and window ventilation. The IFUNAM (Instituto de Física, Universidad Nacional Autónoma de México) Laboratory, where the closed-end cup system for radon was developed, has gained experience though this survey and is willing to share it for future surveys at regional or national levels.

Soil measurements by nuclear track detectors

Abstract In characterization of soil contaminated by transuranics or actinides, some one would be interested in both horizontal and depth distributions. Nuclear Track Detectors (NTDs) are an excellent tool for making inexpensive in-situ measurements. The activity and spatial distribution of such alpha emitting radionuclides as plutonium, americium, and uranium, can be determined. This paper will focus on the methodology for surface mapping and depth profiling of alpha contaminants. The detector material is CR-39. The plastic detectors are placed directly on the soil surface to be measured or inserted into the soil at the measurement point. The detectors may be wedged into a hole punched into the ground or driven into the ground inside of a protective rod. After exposure, the plastic is retrieved, washed with water, and chemically etched overnight in a KOH solution. The lengthwise distribution of etch tracks along the strip is measured to produce a depth profile of the alpha activity. With this methodology it is possible to measure activities below a few Bq per gram, identify hot spots with submillimeter accuracy, and profile distributions to depths of several tens of centimeters. The in-situ measurements produce no radioactive waste and are very low in cost compared to radiochemical methods of analysis.

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.

RADON CONCENTRATIONS IN THE PYRAMID OF THE SUN AT TEOTIHUACAN

Abstract Measurements of radon were taken inside the Pyramid of the Sun of the pre-Columbian Teotihuacan site in Mexico. Beneath the Pyramid of the Sun, there is a prehispanic tunnel that was used for ritual ceremonies. We evaluated the radon levels inside this and other tunnels plus tunnels excavated for research purposes by archaeologists. Passive nuclear track detectors were used to measure radon. Measurements were made in winter during the dry season because the tunnels flood in the rainy season. Radon ranged from 70 to 190 Bq m −3 . The radon levels decreased with height above ground level which probably reflects relatively easy escape routes for radon through the loosely stacked volcanic stores in the outer wall covering.

Studies on the interaction of alpha particles with polycarbonate materials

The interaction of alpha particles irradiation with different commercial polycarbonate foils, from different suppliers was studied, aiming to test the foils as alpha particle detectors, analyzing the effect to the energy to the particles and the response of each material to the chemical etching aimed to reveal latent track. The sensitivity to varying energies and the average backgrounds, which are important parameters to environmental measurements. The efficiency to alpha particles registration and the linearity of the different materials, as referred to the corresponding track density, were compared.

Long-term radon survey in Mexico City and other regions of the country☆

Abstract A long-term survey for indoor radon is ongoing in Mexico City, Guadalajara, Netzahualcoyot, Pachuca, Puebla, Queretaro, Tecamachalco, Tehuacan, Tlaxcala, Toluca, Tula, and Zacatecas. The measurement program started six years ago for a national evaluation of indoor radon problems in the non-tropical regions of Mexico. Most of the houses being monitored have permanently open windows. We also gathered information on geology, topography, building materials, architecture, and ventilation systems. Each of these factors can significantly affect indoor radon concentrations. The passive radon detector is a chip of CR-39 polymer in a closed-end cup. This inexpensive device provides high detection efficiency, and does not require highly skilled training for persons engaged in the deployment and retrieval of the devices. The overall costs of a national survey of indoor radon can, therefore, be kept relatively low. A few of the radon levels (up to 260 Bq m −3 ) are of moderate concern for radon-related health effects. The average of the lower radon concentration levels was 50.6 Bq M −3 , which is most probably due to many houses having permanent openings to the outside.

Intercomparison of response characteristics of seven CR-39 materials during radon calibration

Intercomparison of response is presented for seven different CR-39 polycarbonate materials. All the detector materials were exposed simultaneously to same radon gas inside a calibration chamber under standardized conditions of temperature and relative humidity. Each type of CR-39 was identically developed in etching solution and read with a common system. The efficiencies of track registration were determined experimentally for each material together with background track densities. The etch pit diameter distributions were also determined. Differences in production procedures of the CR-39 make significant differences in response to alpha radiation. It is very important to know the response of each material in order to establish the normalization factors for making radon measurements.

Comparative measurements between NTD and GEL detectors for radon gas

Abstract Because of the interest in an inexpensive radon monitoring technique and the use of new materials and new methods, this work presents comparative measurements between traditional passive radon detector using nuclear track detector (NTD), and a new method based on the diffusion of radon gas in gels, measuring the quantity of the remainder radioactive solids by the analysis of the gamma radiation from the decay of radon daughters. The methodology of the new detectors is introduced. The preliminary results show a measurable response of the gel material detectors to radon gas. The measurements are compared with those using NTDs CR-39 type for calibration purposes. Both the detection systems, the passive close-end cup system with NTDs and the passive close-end cup gel material detector, were exposed at the same time in the radon calibration chamber to different radon exposition levels from 150 to 3000 Bq / m −3 .