J.C. Hadler

Annealing experiments on induced fission tracks in apatite: Measurements of horizontal-confined track lengths and track densities in basal sections and randomly oriented grains

Abstract To improve kinetic models for apatite fission-track annealing, we present new experimental annealing data that complement previously published data. To determine the degree of annealing of induced tracks, surface density (ρ), and mean horizontal-confined track lengths (l), were measured, both for basal and randomly oriented faces. Our annealing data were obtained by submitting an apatite sample collected in Itambé, Bahia, Brazil, to 46 different isothermal treatments where temperature ranged from 150 to 600 °C (duration of 1, 10, 100, and 1000 h). To compare the behavior of Itambé to Durango apatite, the latter was also annealed for 1 h in 9 isothermal experiments at temperatures between 240 and 380 °C. Our results show that the l/l0 values in Durango are systematically smaller than those in Itambé sample, both in basal and random faces. The curves depicting relative track density reduction, ρ/ρ0, and relative mean confined track length reduction, l/l0, as a function of time and temperature, are similar for ρ/ρ0 > ~0.5, but different for ρ/ρ0 < ~0.5. In this interval, ρ/ρ0 can be measured but the measurement of l/l0 is very difficult because the confined tracks become undetectable. Measurements of ρ/ρ0 and l/l0 for tracks revealed in basal surfaces are systematically lower (but this difference is <3%) than those in randomly oriented ones.

Spontaneous-fission decay constant of 238U measured by nuclear track techniques without neutron irradiation

A value of the decay constant for spontaneous fission of 238U, lf, determined by particle-track detector techniques, is presented. The main source of systematic error in fission-track measurements of lf, the so called ‘neutron dosimetry’, has been avoided. Instead of calibrating the neutron source and the usual mica detector through tracks of 235U fission induced by thermal neutrons, spontaneous-fission tracks and alpha-particle tracks of 238U and 242Pu were used. A value of lf = (8.66±0.38)·10-17 y-1 has been obtained.

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.

Fission track analysis of apatites from São Francisco craton and Mesozoic alcaline-carbonatite complexes from central and southeastern Brazil

Abstract Thermal histories on seven Brazilian apatites were obtained by fission track analysis using Monte Carlo simulations. The apatites were collected from two distinct geotectonic provinces. One group, originated from Sao Francisco craton, represents a typical cratonic domain with Proterozoic and Eopaleozoic rocks and yielded Permo-Triassic ages (counted since the instant when temperature was low enough so that the damage produced by fission tracks in apatite started to be preserved). The common thermal history accepted by all samples of this group is a linear cooling from ~90 to ~25 °C for the last 240 Ma, in agreement with present day thermal gradient and denudation rates. The other group, from Mesozoic alkaline-carbonatite complexes, in central and southeastern Brazil, yielded Cretaceous ages, close to those of the intrusions. For the samples of central Brazil, fission track analysis suggests a slow cooling from ~95 ° to ~85 °C between 90 and 60 Ma ago, followed by a faster cooling from ~85 ° to ~27 °C for the last 60 Ma. Otherwise, two trends exist for the samples of southeastern Brazil. The primary one is an increase in temperature from ~75 ° to ~95 °C, which occurred between 140 and 60 Ma ago. In this period, there is also another trend: a cooling from ~100 ° to ~80 °C. However, both trends are followed by a common thermal history during the last 60 Ma: a cooling from approximately ~80 ° to ~25 °C.

A PC compatible Brazilian software for obtaining thermal histories using apatite fission track analysis

Abstract In this work a software developed in the Instituto de Fisica Gleb Wataghin, IFGW, UNICAMP, Campinas, SP, Brazil for obtaining thermal histories using apatite fission track analysis is presented. This software works in Microsoft-Windows environment. It will be freely disposable in the web site of the Departamento de Raios Cosmicos, IFGW, UNICAMP. Thermal histories obtained through this software are compared with those deduced using Monte Trax the software compatible with Apple Macintosh developed by Gallagher.

Spontaneous 238U fission half-life measurements based on fission-track techniques

In the last recommendation of the International Union of Pure and Applied Chemistry (I.U.P.A.C.) on spontaneous fission half-lives for ground-state nuclides, a number of measurements of 238U based on fission-track techniques were discarded. The arguments given by the authors are not clear. In this work a more detailed discussion of these determinations is given, considering the possible systematical errors inherent in fission-track approaches.

On indoor radon contamination monitoring with SSNTDs: Experimental results concerning plate-out and self-plate-out effects

Abstract Measurements of the alpha activities of 222 Rn and its daughters were performed, both inside a glass recipient and in closed rooms, employing SSNTDs (CR-39 and nuclear emulsion). The experimental results presented here show that plate-out and self-plate-out effects should be taken into account when SSNTDs are employed in indoor radon contamination monitoring.

Further investigation of the initial fission-track length and geometry factor in apatite fission-track thermochronology

Abstract The external detector method (EDM) is a widely used technique in fission track thermochronology (FTT) in which two different minerals are concomitantly employed: spontaneous tracks are observed in apatite and induced ones in the muscovite external detector. They show intrinsic differences in detection and etching properties that should be taken into account. In this work, new geometry factor values, g, in apatite, were obtained by directly measuring the ρed/ρis ratios and independently determined [GQR]ed/is values through the measurement of projected lengths. Five mounts, two of which were large area prismatic sections and three samples composed of random-orientation pieces have been used to determine the g-values. A side effect of applying EDM is that the value of the initial confined induced fission track, L0, is not measured in routine analyses. The L0-value is an important parameter to quantify with good confidence the degree of annealing of the spontaneous fission tracks in unknown-age samples, and is essential for accurate thermal history modeling. The impact of using arbitrary L0-values on the inference of sample thermal history is investigated and discussed. The measurement of the L0-value for each sample to be dated using an extra irradiated apatite mount is proposed. This extra mount can be also used for determining the g value as an extension of the ρed/ρis ratio method. Eight apatite samples from crystalline basement, with grains at random orientation, were used to determine the g-values. The results found are statistically in agreement with the values found for apatite samples (from Durango, Mexico) measured in prismatic section and also measured at random orientation. There was no observable variation in efficiency regarding crystal orientation, showing that it is relatively safe using non-prismatic grains, especially in samples with paucity of grains, as it is the case of most basin samples. Implications for the ζ-calibration and for the calibration of the direct (spectrometer-based) fission-track dating are also discussed.

Indoor radon and radon daughters survey at Campinas-Brazil using CR-39: First results

The first results of a radon and radon daughters (RD) survey performed at Campinas-SP, Brazil, are presented. We employed a technique that, potentially, makes possible to measure the radon and RD activity in the air and to separate from this result the activity of radon, alone. In this preliminary paper only the former activity is studied.

A possibility of monitoring indoor radon daughters by using CR-39 as an alpha-spectrometer

Abstract Alpha-spectroscopy using CR-39 has been employed by us in monitoring radon and its daughters. By means of measuring the track diameters (considering only the tracks whose ratio between the major and the minor diameters is ≤ 1.100), one can find the energy distribution of the incident α-particles and, in this way, obtaine information about the plate-out rate of radon daughters on material surfaces and also about the concentration of radon and daughters present in the air. In this work, it is shown how radon and daughters monitoring can be improved by using this technique.