Micro hardness measurements on lead silicate glass

The synthesis of lead silicate glass suitable for fabrication of compression type glass to metal seals has been studied with varying amounts of modifier ions (Na, K and Ba). A three-stage heating schedule was evolved for the preparation of glass. While, some of the constituents were taken in the form of oxides, the others were either in the form of carbonates or nitrates. Dependence of micro hardness of these glasses on the relative content of Na₂O, K₂O and BaO was investigated. The concentration of these oxides was varied in the range 0–16 wt%. The modifier ions were seen to affect the micro hardness in a combplex manner. While the micro hardness of glass without Na₂O and 13 wt% K₂O was found to be 504 kg/mm², it turned out to be 547 kg/mm² for a glass with 13 wt% of Na₂O in the absence of K₂O. However, the micro hardness of the glass synthesized having optimum composition with oxides of Na, K and Ba in the proportion of 5, 8 and 4 wt%, respectively was 455 kg/mm². The glass powder was found to be suitable for making single- and multi-pin seals which could withstand pressures up to 1·2×10⁴ psi and vacuum of 10⁻⁸ Torr.     

Soil radon measurements in the Canadian cities

Radon has been identified as the second leading cause of lung cancer after tobacco smoking. Information on indoor radon concentrations is required to assess the lung cancer burden due to radon exposure. Since radon in soil is believed to be the main source of radon in homes, measurements of soil gas radon concentrations can be used to estimate variations in radon potential of indoor environments. This study reports surveys of natural background variation in soil radon levels in four cities, Montreal, Gatineau, Kingston and the largest Canadian city of Toronto. A total of 212 sites were surveyed. The average soil gas radon concentrations varied significantly from site to site, and ranged from below detection limit to 157 kBq m(-3). For each site, the soil radon potential (SRP) index was determined with the average soil radon concentration and average soil permeability measured. The average SRP indexes are 20±16, 12±11, 8±9 and 12±10 for Montreal, Gatineau, Kingston and Toronto, respectively. The results provide additional data for the validation of an association between indoor and soil radon potentials and for the development of radon potential map of Canada.     

氡的性质及空气中氡浓度的测量综述

本文描述了氡的性质、危害及其在空气中浓度的测量方法，并对测量中应注意的问题提供了一些思考与建议。     

Hourly indoor radon measurements in a research house

This paper reports and discusses the behaviour of radon concentration with time in an uninhabited dwelling. The relationship between variations in radon concentrations and indoor-outdoor temperatures and wind intensity has also been discussed. Radon concentration was measured hourly in a house located at a height of 800 m in the Lombard Prealps, at the top of the Valassina valley. The wind velocity and indoor-outdoor temperatures were measured by means of a meteorological station located on the terrace of the house. The data were analysed using the LBL model for indoor-outdoor air exchange and the models for the indoor accumulation of radon due to exhalation from building materials and pressure-driven infiltrations located underground. The role of wind and indoor-outdoor temperatures were analysed. The agreement of measurements with modelling clearly demonstrates the importance of the different sources of indoor radon. As the investigation was conducted in an uninhabited house, the measurements were not affected by the behaviour of people, e.g. opening and closing of windows. Measurements of the outdoor atmospheric concentrations of (222)Rn provide an index of the atmospheric stability, the formation of thermal inversions and convective turbulence.     

Long-term measurements of radon equilibrium factor in Greek dwellings

The time variation of the radon equilibrium factor F was measured every four hours in the Nuclear Technology Laboratory of the Aristotle University of Thessaloniki (in northern Greece) during October 1998-April 1999. The time dependence of the mean weekly value of radon equilibrium factor F is relatively small. During October 1999-May 2000 the radon equilibrium factor was measured in 25 apartments randomly distributed in Thessaloniki. The mean value of the equilibrium factor F is 0.47 +/- 0.09, close to the typical value of 0.4 adopted by UNSCEAR.     

Analytical developments for high-precision measurements of W isotopes in iron meteorites

A procedure was developed to accurately measure the W isotopic compositions of iron meteorites with a precision of better than +/-0.1 epsilon on epsilon182W and epsilon184W (normalized to 186W/183W). Purification of W was achieved through a two-step, ion-exchange procedure. In most cases, the yield is better than 80%, and purified W solutions are clear of matrix elements and direct isobars of W. The final W solutions were analyzed using a Micromass Isoprobe multicollector inductively coupled plasma mass spectrometer (MC-ICPMS). Tests performed on mixtures of terrestrial standards and meteorite samples demonstrate that the method is accurate and that epsilon182W variations as small as approximately 0.1 epsilon can be detected. Analyses of three different aliquots of the Gibeon (IVA) iron meteorite obtained over a period of 6 months show identical epsilon182W values with a weighted mean of 3.38 +/- 0.05, consistent with literature data for IVA iron meteorites, and indicating that the metal-silicate differentiation event in its parent body was either contemporaneous with or slightly postdated (by up to approximately 2.5 My) the formation of refractory inclusions. We demonstrate our ability to measure epsilon184W accurately and precisely (within +/-0.1 epsilon), which is useful for characterizing cosmogenic and nucleosynthetic effects that may be present in iron meteorites. We also report for the first time measurements of epsilon180W, albeit with large error bars (<+/-4 epsilon, in most cases).     

New technique for the determination of radon diffusion coefficient in radon-proof membranes

This paper describes a new device and a method to determine the radon diffusion coefficient in damp-proof membranes developed in the Czech Republic. The main advantage of the device is that it enables tests to be carried out in all the known measuring modes used throughout Europe. Two recently developed computer programs are presented for the numerical modelling of the time-dependent radon transport through damp-proof membranes. According to this method, the radon diffusion coefficient is derived from the process of fitting the numerical solution to the measured curve of radon concentration in a receiver container. Numerical simulation and measured data are also compared. Reasons for disagreements between different methods and specific configurations of the measuring device are also discussed.     

Indoor and soil gas radon simultaneous measurements for the purpose of detail analysis of radon entry pathways into houses

Detailed knowledge of radon transport mechanisms from the subsoil into the indoor environment is essential for the correct interpretation of results of short-term indoor radon measurements and for proper and effective design of radon mitigation systems. Radon transfer factor time variations have been studied based on simultaneous continuous indoor and soil gas radon measurements within the framework of complex radon diagnosis of individual buildings. In this context, the key influencing factors have been identified and analysed in order to provide satisfactory explanation on radon entry variations under different measurement conditions. Moreover, a new significant manner of radon entry into the indoor environment has been identified and will be discussed in detail.     

Crystallization of boro-silicate glass containing lead oxide

Glass of molecular percent composition 7B₂O₃-92.5 SiO₂-0.5 PbO was heat-treated at 600°C and 650°C for different lengths of time. Transmission electron microscopic studies revealed that phase separation is a precursor to crystallization in this glass.     

Freezing of molecular hydrogen and its isotopes in porous vycor glass

We have made a detailed ultrasonic study of freezing and melting of molecular H₂, HD and D₂ in the pores of Vycor glass. The behavior was similar to that seen in previous measurements with argon and helium. The hydrogen liquids under cooled about 2.5 K below their bulk triple points before freezing began and there was substantial hysteresis between freezing and melting. The velocity and attenuation began to increase suddenly at the onset of freezing. The velocity continued to increase to the lowest temperatures (2 K) and the attenuation had a broad peak at about two thirds of the freezing temperature. We attribute these effects to stress relaxation via thermally activated vacancy motion in the solid hydrogen, an interpretation confirmed by looking at the frequency dependence of the velocity and attenuation. The magnitude of the velocity and attenuation changes increased in going from H₂ to HD to D₂, as expected based on their increasing densities and elastic constants. However, there were no qualitative differences between the boson (H₂ and D₂) and fermion (HD) cases nor, for that matter, between hydrogen and argon. We believe that essentially all the hydrogen was frozen a few tenths of a kelvin belowT _F, at the point where the melting/freezing hysteresis began. If even a few per cent of the hydrogen had remained liquid and become superfluid at some lower temperature, it would have been seen as a further increase in the velocity and a critical attenuation peak. The sensitivity of our ultrasonic measurements allowed us to make accurate measurements of the freezing and melting temperatures of the different liquids in Vycor. We found that the fractional undercooling, (T _B -T _F )/T _B , increased as the molecular mass decreased which may indicate the importance of quantum effects on the liquid-solid interfacial energy _ls .     

Stress measurements in glass using shaped-charge jets

Stresses were measured in glass targets in the vicinity of a penetrating shaped-charge jet. Stress levels of approximately 0.3 GPa were measured 12–20mm away from a jet formed by a 35mm copper liner. High speed framing camera photographs showed that the penetration velocity in the glass was 2.57 km/s and the glass fracture velocity was 2.10 km/s.     

Crystallization as a way for inducing thermoluminescence in a lead borate glass

A great improvement in thermoluminescence response was found, for the first time, for crystallized samples of lead borate glass of composition 33% PbO and 67% B₂O₃ (% in mol); this response clearly increases with crystallization time. Glass–crystal transformation was characterized by thermal analysis and by scanning electron microscopy. Results indicate the studied lead borate glass–ceramic as a promising material for thermoluminescence dosimetric applications.     

Logistic of surveys of retrospective radon concentrations by home-stored CDs/DVDs

Recently, a method for rather precise retrospective (222)Rn measurements, based on home-stored compact disks (CDs)/DVDs, has demonstrated a promising potential for wide application. In Bulgaria, pilot surveys have been initiated based on voluntarily provided CDs/DVDs. The results showed that large-scale surveys could be efficiently organised. However, several problems were identified and are discussed in the report. The first is the relatively small proportion of participants (30-50 %) that actually provided disks. Other addressed topics include the compatibility between results of different disks from one place, the accuracy of dating CDs/DVDs and the possibility for individual a posteriori calibration of each disk. The possibility to follow year-to-year variations by disks of different age is also discussed.     

High resistance lead glass tubing for rich counters and for electromagnetic calorimeters

We have developed a manufacturing process for arrays of high resistance lead glass tubing for positron emission tomography research. We describe two applications of this type of device in high energy physics: as an active photon shield in Cherenkov imaging detectors and as a drift collection electromagnetic calorimeter.     

Preparation and study of superficially coloured lead glass

Superficially coloured lead crystal glass was obtained by ion-exchange with silver. Both red and yellow ruby colouring were achieved by the presence of small silver particles (colloids) dispersed into the ion-exchanged glass surface. Direct silver ion-exchange of the glass yielded yellow colouring (optical absorption around 410 nm). Silver ion-exchange of lead glass previously doped with a reducing agent (i.e., arsenic oxide) yielded red colouring, (optical absorption around 600 nm), which indicated special arrangement for silver colloids in the exchanged layer. Parameters that influenced the ion-exchange process, such as temperature, exchange time, dopant percentage and composition of molten salts bath (where the ion-exchange took place), were examined in order to select the best conditions to obtain colours with decorative interest. Optical absorption spectroscopy and scanning electron microscopy were used to determine colour coordinates and silver diffusion profiles, respectively. Direct observation of the silver colloids were performed by means of transmission electron microscopy. Finally, once the optimum process parameters were tested, an intense red ruby colouring (more than 98% colour purity) was reached. Industrial application of this process arises positively, since some handicaps from traditional bulk colouring could be avoided.     

Thick source alpha counting using fused glass discs: corrections for loss of radon and polonium

Thick-source alpha counting can be used for the assay of low level U and Th in soils, rocks and similar materials. An effective method of preparing samples for this purpose is to fuse them in a lithium borate glass. The present paper discusses the loss of radon and polonium activity during fusion at elevated temperatures. A time dependent factor is given to correct for the loss of radon and polonium.     

Indoor radon concentrations in Poland as determined in short-term (two-day) measurements

The aim of the present work was to obtain a pattern of 222Rn concentration distributions in typical buildings in Poland. In the investigations, the environmental passive detectors of the PICO-RAD type were used. The study encompassed buildings that were typical for Poland. The distribution of airborne 222Rn concentrations indoors is of a log-normal type. A total 1171 detectors were measured. Measurements were made in 319 basements, the remaining 852 measurements were carried out in the inhabited part of the houses. The radon concentrations in the basements in Bq x m(-3) ranged from 6 to 1300 with the arithmetic mean AM = 60, geometric mean GM = 30 and median M = 28, whereas those in the inhabited parts of the house (above the ground level) were: AM = 25, GM = 17 and M = 16 with the highest record value of 420.