Natural Thermoluminescence Research Articles

The natural thermoluminescence of Antarctic meteorites and their terrestrial ages and orbits: A 2010 update

Abstract– We have examined the relationship between natural thermoluminescence (TL) and 26Al in 120 Antarctic meteorites in order to explore the orbital history and terrestrial ages of these meteorites. Our results confirm the observations of Hasan et al. (1987) which were based on 23 meteorites. For most meteorites there was a positive correlation between natural TL and 26Al, reflecting their similarity in decay rate under Antarctic conditions and thus in terrestrial age. For a small group with low TL and high 26Al a small perihelion was proposed. Within this group, natural TL decreases with terrestrial age as determined by 36Cl measurements, although the rate of TL decay is faster (half‐life approximately 10 ka) and the ages that can be determined are smaller (<200 ka) than for most meteorites. The faster decay rate and lower natural TL levels are a reflection of recent exposure to higher radiation doses and higher temperatures, since this history would populate less stable TL traps with smaller electron densities. We sort the 120 meteorites by perihelion and terrestrial age. The normal perihelion group range up to approximately 1000 ka and the small perihelion group range up to approximately 200 ka. An intermediate perihelion group tends to have short terrestrial ages (20–60 ka). There is acceptable agreement between most (34 out of 43) of our present terrestrial age estimates and those determined by isotopic means, the exceptions reflecting complex irradiation histories, long burial times in the Antarctic, or other issues.

Thermoluminescence Study of Base Materials of Ceramic Tiles

Many flooring materials most of them are in natural form are used to manufacture floor tiles for household flooring purpose. The peoples demand for variety of flooring material Leeds to develop various types of ceramic tiles. In India ceramic industry is fast growing one, more then 400 units of manufacturing ceramic tiles, vitrified tiles and sanitary ware, situated around Morbi, Rajkot, Gujarat, India. Many natural minerals are used as the raw materials required for the manufacturing ceramic ware. The following minerals are used to manufacturing the ceramic tiles i.e. Quartz, Feldspar, Zircon, Talc, Grog, Alumina oxide, etc. Most of the minerals are from Indian mines of Gujarat and Rajasthan states, some of are imported from Russian sub continent. The present paper reports the thermoluminescence (TL) characteristics of Feldspar, Alumina and Quartz minerals collected from the ceramic tiles manufacturing unit, Morbi. The as received minerals Natural TL was recorded (NTL), and annealed and quenched from 400 °C and 800 °C followed by 15Gy beta dose given from Sr-90 beta source TL was recorded and the comparative TL (Thermoluminescence) study of above materials are presented. The characterization of the minerals is done using TGA and XRD studies.

Correlation between thermoluminescence sensitivity and crystallization temperatures of quartz: Potential application in geothermometry

Abstract The thermoluminescence (TL) characteristics of quartz are highly dependent of its thermal history. Based on the enhancement of quartz luminescence occurred after heating, some authors proposed to use quartz TL to recover thermal events that affected quartz crystals. However, little is know about the influence of the temperature of quartz crystallization on its TL characteristics. In the present study, we evaluate the TL sensitivity and dose–response curves of hydrothermal and metamorphic quartz with crystallization temperatures from 209 ± 15 to 633 ± 27 °C determined through fluid inclusion and mineral chemistry analysis. The studied crystals present a cooling thermal history, which allow the acquiring of their natural TL without influence of heating after crystallization. The TL curves of the studied samples present two main components formed by different peaks overlapped around 110 °C and 200–400 °C. The TL sensitivity in the 200–400 °C region increases linearly with the temperature of quartz crystallization. No relationship was observed between temperatures of quartz crystallization and saturation doses (

Quartz Thermoluminescence—Another Potential Paleo‐Thermometer for Studies of Sedimentary Basin Thermal History

AbstractGood reproducibility of quartz thermal stimulated luminescence phenomenon offers the possibility of dating geological events in the subsurface and exploring environmental temperature history. As sandstones in basins generally experienced one certain pattern of thermal history due to effects of temporal and spatial dependent temperature fields, the quartz minerals extracted from these sandstones can be evaluated to explore the thermal regime structure information by thermoluminescence analyzing technique. In terms of equivalence for certain burial depths in the petroleum basin, the mean quantitative temperature field was investigated using both the quartz thermoluminescence apparent age method and laboratory isothermal thermoluminescence simulation measurements. The result shows that the variations of both thermoluminescence glow‐curve pattern and intensity of certain natural thermoluminescence peaks correlate well with the environmental temperature field at corresponding burial depths where the quartz grains were extracted. The quartz natural thermoluminescence glow‐curves peaks shift to high temperature and the thermoluminescence intensity reduction results from the increase of both environmental temperature and burial time for quartz due to deepening burial depth. Both the additive dose thermoluminescence (TL) and isothermal TL (SA‐ITL) techniques were used for quartz mineral TL dating and the resultant apparent ages agree well with each other, and thus one parameter called equivalent temperature was tentatively presented and deducted from apparent TL ages of quartz minerals to evaluate the basin's thermal regime structure. Quartz thermoluminescence signal can be recognized as one potential paleothermometer if the good correlation of calculated equivalent temperature of buried quartz mineral with other paleothermometers can be supported by more lines of future independent geological evidence.

Investigation of the Sediment Movement along the Tenryu–Enshunada Fluvial System Based on Feldspar Thermoluminescence Properties

The thermoluminescence (TL) properties of feldspar were used to investigate the sediment movement processes in a fluvial–coastal system. Field samples were collected at various locations along the Tenryu River and the Enshunada Coast in Japan. After a series of pretests, an appropriate TL measuring sequence was proposed for this study. Applying this approach, the natural TL intensity of feldspar grains was measured. Owing to the young age of the research area, it was assumed that the natural TL difference was ascribed to the sample depositional environment under which different possibilities of sunlight exposure exist. Surface sediment particles in the target area were classified into three groups in terms of TL intensities, i.e., river sand with large TL signals, coastal sand with medium TL signals, and dune sand with small TL signals. Stratified configuration of the Nakatajima Coastal Dune was observed from the underground-sample TL glow curves with a top, windblown, dune-sand layer; a bottom, wave-induced, coastal sand layer; and a mixing layer in between. A rather complex sediment-movement pattern in front of the Tenryu River mouth was revealed after investigation of the underwater samples. Because of the seawater influence, acting as an ultraviolet filter to sunlight, underwater samples present a larger, high-temperature TL peak than the low-temperature peak; whereas these two are almost the same for ground samples.

Thermostimulated luminescence characteristics of dolomitic rocks and their use as a gamma ray dosimeter

The thermostimulated luminescence (TSL) glow curve characteristics of ten dolomitic crystals of Salem and Namakkal districts of Tamilnadu are analysed. The natural thermoluminescence (NTL) measurements were carried out for all the samples and show two peaks at 270 °C and 335 °C. The sample irradiated with a gamma dose of 200 Gy shows an additional peak at 180 °C, when recorded with linear heating rate of 10 °Cs −1. At the same time, the NTL peak at 270 °C is shifted to 260 °C while increasing in intensity and there is no change in the peak position of 335 °C. The annealed sample also shows the same trend. The sample was annealed in air at the temperatures ranging from 200 to 950 °C, at an interval of 50 °C, for 1 h duration. Annealing treatment above 250 °C increases the sensitivity of all three TSL peaks. On the other hand, annealing at 800 °C caused a collapse in the TSL sensitivity. The enhancement in TSL sensitivity was found to depend on the annealing temperature and time. Annealing treatment at 700 °C for 4 h followed by quenching in air is the optimum condition for TSL sensitization. The response to gamma irradiation is linear in the range from 0.5 to 10 4 Gy. The number of glow peaks was identified through partial heating method. Using peak shape and initial rise method the kinetic parameters (activation energy (E), frequency factor (S) and order of kinetics (b)) were evaluated. The investigations show that the trapping centers are not affected by the annealing procedure. The emission spectra of all the samples show an emission at around 608 nm but with different intensities for each sample. With reference to earlier work, it may be assumed that the recombination site always involves Mn 2+ ions.

SPECTROSCOPY OF TRAPS IN COLORLESS MICROCLINE AS DETERMINED BY CGCD AND VHR

Glow curves of natural thermoluminescence (NTL) of colorless microcline (triclinic form of KAlSi 3 O 8 feldspar) have been subjected to the rigorous Computerized Glow Curve Deconvolution (CGCD) in the framework of kinetic formalism and Various Heating Rates (VHR) methods to compare the spectroscopy of traps. It is observed that trapping parameters obtained by the two methods are coincident, which is well-supported by the standard error analyses, i.e., Figure of Merit (FOM) and Chi-square test. Further analysis shows that the value of Urbach's constant (Um) is no more constant in the present case for the whole temperature range, but has certain values for a certain temperature zone.

Natural blue thermoluminescence emission of the recently fallen meteorite in Villalbeto de la Peña (Spain)

This paper reports on the thermal stability of the natural blue thermoluminescence (TL) of a well-characterised meteorite fallen in Villalbeto de la Peña (Palencia, Spain) in January 4, 2004. The meteorite specimen exhibits a complex structure of the spectra emission a wide broad maximum peaked at about 320 °C that can be associated with consecutive breaking linking of bonds (e.g. of Al–O, Cr–O, Fe–O) from lattices of several phases, i.e., olivine, low-Ca pyroxene, plagioclase and redox reactions. The natural TL emission seems to be essentially caused by the Na–Ca plagioclase as the brighter material inside this L6 chondrite. The thermal stability tests, at different temperatures, confirm a continuous trap distribution with progressive changes in the glow curve shape, intensity and temperature position of the main peak. In consequence, the glow curve analysis methods commonly used for synthetic materials based on single-discrete traps cannot be applied for this material.

Potential health risk in areas of high natural concentrations of thallium and importance of urine screening

There is a lack of information in the literature regarding Tl exposure from naturally occurring Tl enrichment. This paper draws attention to the potential health risk posed by high concentrations of naturally occurring Tl in the environment. The inhabitants of a rural area in SW Guizhou Province, China, reside within a natural Tl accumulated environment resulting from Tl-rich sulfide mineralization, and they face ongoing severe Tl exposure. High Tl concentrations were detected in urine of the local residents. Urinary Tl concentrations are as high as 2668 μg/L, with most subjects surpassing the accepted world urinary Tl concentration at <1 μg/L for “non-exposed” humans. The urinary Tl concentrations show significant differences among three communities ( n = 21, p = 0.001), but no significant difference in either sex or age groups ( n = 21, p = 0.7806). However, there is a positive statistical relationship between the extent of Tl exposure from Tl concentrations in soil and crops in the immediate environment and the concentrations of Tl detected in urine. A majority of the volunteer subjects from the communities have urinary Tl concentrations above 4.5–6 μg/L, implying early adverse health effects, and some of them have over 500 μg/L urinary Tl, considered to be at/about the level of clinical intoxication. This study has been able to identify that the elevated urinary Tl concentrations are mainly attributable to Tl accumulation in locally grown vegetables, which acquire Tl from the soil. This study also shows that Tl in urine of the local population represents a steady-state condition with long-term exposure, and that urinary Tl concentrations can be taken as a bio-marker of total dose based upon total daily dietary intake. This study demonstrates that natural sources of elevated Tl pose a potential health risk to the population, and that monitoring the urinary Tl concentration is a reliable and accurate way of bio-marking Tl exposure.

TL dating of feldspars using their far-red emission to deal with anomalous fading

New studies of thermoluminescence (TL) dating of feldspars involving their far-red emission are proposed. The intense TL of feldspars is affected by the pervasive effect of anomalous fading, a strong deterrent to their use for TL dating. With volcanic feldspars, the natural TL can fade completely. With other feldspars, such as found in sediments, anomalous fading may turn out to be weaker and correct TL dates could be obtained. This effect of fading may be dealt with methods based on the little studied far-red emission, a band centred around 710 nm present in the TL of all feldspars. Apparently this emission does not fade during geological storage, or at least much less than the visible and UV (‘blue’) emissions used by conventional TL, OSL or IRSL readers. This emission has enabled dating by TL and has been expanded to IRSL. These TL experiments are resumed with improved methods for filtering, collection of data and protocols. Firstly, the stability of TL in some sediments is tested by the B ir protocol. B ir is the ratio of the conventional ‘blue’ emission to the far-red emission measured simultaneously in the course of a TL measurement by use of filters on a carousel. Comparison of the values of B ir between prompt TL and the natural TL provides a sensitive gauge of the stability of conventional TL, which is verified notably with some sediments dated by Preusser [IRSL dating of K-rich feldspars using the SAR protocol: comparison with independent age control. Ancient TL 21, 17–23.]. Secondly, two volcanic plagioclases of known age from Olby and Royat are considered. In their natural TL, the conventional ‘blue’ emission has drastically faded away but not the far-red one. Additive TL using this far-red emission leads to a satisfactory evaluation of the natural dose of these samples, hereby confirming the stability of this far-red emission during geological storage.

Red TL of quartz extracted from Chinese loess: Bleachability and saturation dose

The red TL of quartz has been shown to exhibit a much higher saturation dose than that of the UV emission in quartz, and thus has the potential to considerably extend the dating range. Unlike heated materials, in which the luminescence signal has been completely thermally reset, the quartz red TL from Aeolian sediments accumulates on top of a residual signal left after daylight bleaching. The characteristics of this bleaching process must be investigated before any dating attempts can be made. It is demonstrated in this paper that the red TL of quartz extracted from Chinese loess: (1) bleachable by sunlight, but with high residual level. Up to about 40% of the natural signal remains after bleaching in our sample; all of the broad natural TL peak bleaches simultaneously in sunlight; (2) has significant dose-dependent sensitivity change when laboratory doses beyond 1500 Gy are applied; this sensitivity change cannot be corrected for by a test dose; and (3) has a D 0 value of ∼ 550 Gy , much larger than that of optically stimulated luminescence (OSL) ( ∼ 90 Gy ) from the same sample.

CATHODOLUMINESCENCE AND THERMOLUMINESCENCE STUDIES OF CLAY MINERALS

Cathodoluminescence (CL) measurements of clay minerals were performed at both room temperature and low temperature. Panchromatic CL images of kaolinite and dickite show blue emission at room temperature. Their CL spectra exhibit an intense broad band peak at around 375 nm. This emission band related to radiation induced defect centers (RID) disappears at low temperature. Effect of sample temperature on CL intensity of kaolinite and dickite can not be interpreted on the basis of a temperature quenching theory. In halloysite, serpentine minerals, sericite and sepiolite, the intensity of a broad band between 400 and 450 nm is higher at low temperature than at room temperature. CL spectra of serpentine minerals are characterized by a broad band centered at 720 nm, which can be assigned to Fe 3+ impurity center. Natural TL glow curve of sepiolite presents two glow peaks around at 210 and 260°C in the high temperature region, of which intensities are weak. This implies that it is rather a possibility of applying TL of sepiolite to the dating. The other minerals show no emission in natural TL measurements. X-ray induced TL of kaolin minerals exhibit intense several TL glow peaks below room temperature. Serpentine minerals have glow curves with a relative large peak between 70 and 90°C. Sericite, montmorillonite and sepiolite show a combination of emission peaks in their TL glow curves, while their intensities are weak compared to kaolin and serpentine minerals. Clay minerals might have characteristic TL related to their crystal structure.

Optical absorption, TL and IRSL of basic plagioclase megacrysts from the pinacate (Sonora, Mexico) quaternary alkalic volcanics

The paper presents the first results of an investigation on optical absorption (OA), thermally and infrared stimulated luminescence (TL and IRSL) of the Pinacate plagioclase (labradorite). The OA spectra reveal two bands with maxima at 1.0 and 3.2 eV connected with absorption of the Fe3+ and Fe2+ and IR absorption at wavelengths longer than 2700 nm. The ultraviolet absorption varies exponentially with the photon energy following the 'vitreous' empirical Urbach rule indicating exponential distribution of localised states in the forbidden band. The natural TL is peaked at 700 K. Laboratory beta irradiation creates a very broad TL peak with maximum at 430 K. The change of the 430 K TL peak shape under the thermal cleaning procedure and dark storage after irradiation reveals a monotonous increasing of the activation energy that can be explained by the exponential distribution of traps. The IRSL response is weak and exhibits a typical decay behaviour.

Quartz red TL SAR equivalent dose overestimation for Chinese loess

For the red TL of quartz extracted from Chinese loess, the single-aliquot regenerative-dose (SAR) procedure overestimates the known laboratory doses in dose recovery test. The overestimation is the result of the first heating during the measurement of natural TL signal causing a sensitivity reduction, which is not corrected for using a SAR protocol. The SARA procedure was used to measure the sensitivity change. Using this as a correction factor is tested by comparison with the quartz optically stimulated luminiscence (OSL) equivalent dose. SARA is also employed to determine the residual level of red TL, which is found to be more than 100 Gy.

Effects of gamma-irradiation on the TL characteristics of pre-annealed natural ZrSiO4

By the use of thermoluminescence (TL) technique we have investigated the effects of gamma irradiation on the TL response of pulverised natural zircon (ZrSiO4) crystals from the Jos Plateau area of Nigeria. Samples of the mineral that have been previously annealed were artificially irradiated to moderate gamma doses ranging from 0.7 to 4.9Gy using 60Co gamma-source of the CERD. The natural TL glow curve of the sample showed a broad peak around 250°C, the peak was however, found to be completely erased following heat treatment for 2h at 400°C. The TL glow curves of the artificially irradiated samples showed two overlapping glow peaks at about 112°C (peak I) and at 156°C (peak II) within the dose range utilised. We note that the natural TL peak appears to be different from the two observed in the artificially irradiated sample. The TL response with dose was investigated for the two glow peaks found in the artificially irradiated sample and in both cases, in the dose range utilised, linear relationship was obtained. The fading pattern of the two peaks was also monitored over a period of 28 days. The change in TL response with storage time was found to be somewhat anomalous especially within the first 24h after exposure to irradiation. Consequently, we have fitted the fading curves beyond that anomalous region to analytical equations that could then be used in predicting the change in TL intensity with storage time. The implications of these results in terms of the potential of Nigerian zircons for applications in TL dating and radiation dosimetry are briefly discussed.

Thallium isotope composition of the upper continental crust and rivers—An investigation of the continental sources of dissolved marine thallium

The thallium (Tl) concentrations and isotope compositions of various river and estuarine waters, suspended riverine particulates and loess have been determined. These data are used to evaluate whether weathering reactions are associated with significant Tl isotope fractionation and to estimate the average Tl isotope composition of the upper continental crust as well as the mean Tl concentration and isotope composition of river water. Such parameters provide key constraints on the dissolved Tl fluxes to the oceans from rivers and mineral aerosols. The Tl isotope data for loess and suspended riverine detritus are relatively uniform with a mean of ε 205Tl = −2.0 ± 0.3 (ε 205Tl represents the deviation of the 205Tl/ 203Tl isotope ratio of a sample from NIST SRM 997 Tl in parts per 10 4). For waters from four major and eight smaller rivers, the majority were found to have Tl concentrations between 1 and 7 ng/kg. Most have Tl isotope compositions very similar (within ±1.5 ε 205Tl) to that deduced for the upper continental crust, which indicates that no significant Tl isotope fractionation occurs during weathering. Based on these results, it is estimated that rivers have a mean natural Tl concentration and isotope composition of 6 ± 4 ng/kg and ε 205Tl = −2.5 ± 1.0, respectively. In the Amazon estuary, both additions and losses of Tl were observed, and these correlate with variations in Fe and Mn contents. The changes in Tl concentrations have much lower amplitudes, however, and are not associated with significant Tl isotope effects. In the Kalix estuary, the Tl concentrations and isotope compositions can be explained by two-component mixing between river water and a high-salinity end member that is enriched in Tl relative to seawater. These results indicate that Tl can display variable behavior in estuarine systems but large additions and losses of Tl were not observed in the present study.

Distribution of natural and anthropogenic thallium in the soils in an industrial pyrite slag disposing area

The total concentrations combined with the chemical speciation of thallium (Tl) were examined in order to track the distribution of natural and anthropogenic Tl in the soils in an industrial pyrite slag disposing area. Their geochemical behaviors in the soils were further discussed. Soil samples were collected from three soil profiles adjacent to a large open-disposed pile of industrial Tl-rich pyrite slag, and from one soil profile in the background area. The results show that the soil contamination with Tl derived from slag (slag-Tl) is generally limited; slag-Tl was mainly accumulated in the upper part (<16.5 cm) of the vicinal soils of the slag pile and shows large variation in concentration among different sampling sites. Basically, the soils surrounding the slag pile within 5 m are more Tl-contaminated than those under the slag pile and those far away from the slag pile. In respect of the concentrations of total Tl, the deeper soils of the studied profiles seem to be uncontaminated. However, the percentages of Tl in the easily reducible fraction indicate that these soils have been actually contaminated by slag-Tl. Natural Tl and anthropogenic Tl are distributed differently among the soil components in the studied soils. Natural Tl in the background soils is predominantly hosted in the residual fraction (∼98%), while anthropogenic Tl was significantly incorporated into the more labile fractions of the soil (up to ∼80%), especially in the acid-extractable fractions and easily reducible fraction (up to ∼30% and ∼45%, respectively). Detailed analysis of speciation data of Tl suggests that despite being predominantly controlled by the degree of Tl pollution, the distribution of slag-Tl in the soils can be further affected by the general differences in soil properties. In this study, the order for preferential immobilization of anthropogenic Tl among major soil components can be roughly summarized as: Tl(III) carbonates and hydroxides>Mn oxide–hydroxides>Fe oxide–hydroxides>adsorption sites on the surface of soil, while the order can be significantly mediated by the pH conditions in the soils. The correlations between the fractions of Tl in the slag and in the soils indicate that the anthropogenic Tl in the soils in the studied slag disposing area should be mainly derived from the dissolved slag-Tl that was leached by rainwater rather than from the washed-out particles of slag.

Effect of annealing in thermostimulated luminescence (TSL) on natural blue colour calcite crystals

The thermostimulated luminescence (TSL) glow curve characteristics of 10 blue coloured calcite crystals of Southern Tamilnadu are analysed. The natural thermoluminescence (NTL) measurements were carried out for all the samples and annealed in air at the temperatures ranging from 200 to 700 °C, at an interval of 50 °C, for 1 h duration. The glow curves of annealed and unannealed samples irradiated with a gamma dose of 500 Gy show three peaks at 145, 255 and 345 °C, respectively, when recorded with a linear heating rate of 10 °C/s. Annealing treatment above 400 °C increases the sensitivity of all TSL peaks except 345 °C. On the other hand, annealing at 700 °C caused a collapse in the TSL sensitivity. The enhancement in TSL sensitivity was found to depend on the annealing temperature and time. Annealing treatment at 600 °C for 5 h followed by quenching in air is the optimum conditions for TSL sensitization. The response to gamma irradiation is linear in the range from 1 to 10 4 Gy. The emission spectra of all the samples show an emission at around 610 nm but with different intensities for each sample. With reference to earlier work, it may be assumed that the recombination site always involves Mn 2+ ions.

Environmental concerns related to high thallium levels in soils and thallium uptake by plants in southwest Guizhou, China

Thallium (Tl) contamination in soils poses a significant threat to human health due to the high toxicity of Tl and its ready assimilation by crops. This study is focused on high concentrations of Tl in soils in the Lanmuchang area of southwest Guizhou, China, which is related to natural processes of Tl-rich sulfide mineralization. Thallium contents range from 40 to 124 mg/kg in soils originating from the mining area, from 20 to 28 mg/kg in slope wash materials, from 14 to 62 mg/kg in alluvial deposits downstream, from 1.5 to 6.9 mg/kg in undisturbed natural soils and <0.2 to 0.5 mg/kg Tl in soils from the background area. These values indicate that both the erosion of natural soils from the Tl mineralized area and the mining activity are responsible for the distribution of high Tl concentrations in soils. Two other important toxic metals of interest, mercury and arsenic, also show high contents in soils, and are generally higher than Tl concentrations. Thallium concentration in plants exhibit species-dependent preferences. Thus, the enrichment of Tl in the edible parts of crop species decreases in the following order: green cabbage>carrot>chili>Chinese cabbage>rice>corn. The highest level of Tl in green cabbage is up to 500 mg/kg as dry wt., surpassing the values of Tl in the soils in which the green cabbages grow. In contrast, Hg and As are relatively less concentrated in local plants. The average daily uptake of Tl by the villagers of the Lanmuchang area through consumption of locally planted crops has been estimated to be 1.9 mg/person, which is 50 times the daily ingestion of individuals from the Tl-free background area. The daily ingestion of As and Hg from the study area are 0.03 and 0.01 mg, respectively. This indicates that Tl in the contaminated soils related to the natural Tl mineralization is being readily transferred to the human body through the food chain, and poses a significant threat to the health of the local villagers. Arsenic may pose a lesser health hazard, but mercury has an insignificant health risk. This study illustrates a real environmental concern related to land use and human health in areas containing high contents of Tl in soils associated with the natural occurrence of Tl-rich sulfides and coals, with or without mining activities. Thallium contamination in soils should be a critical parameter for proper land use and health related environmental planning and regulations.

Application of Laser Ablation ICP‐MS to U‐Th‐Pb Dating of Monazite

Recent advances in laser ablation ICP‐MS techniques allow accurate U‐Th‐Pb age dating of monazites that are as young as several tens of million years to a precision better than 2%. Accuracy of the age determinations has been improved by true real‐time mass bias correction via nebulisation of a solution containing enriched 233U and natural Tl isotopes. The Tl‐U tracer solution eliminates possible effects of variable sample matrices on the precision and accuracy of measured isotopic ratios. Mass bias corrections based on measured 205Tl/233U ratios in the tracer solution allow direct measurement of 235U in monazite. Combined with high‐sensitivity laser ablation ICP‐MS measurements, direct measurement of 235U particularly improves the precision of U‐Pb dating of young monazites. Correction for laser‐induced Pb/U and Pb/Th elemental fractionation is based on a mathematical treatment of time resolved count‐rate data that is independent of laser ablation characteristics, does not require external standardisation and allows variable laser pit size or raster patterns for each measurement. The new procedures make the LA ICP‐MS technique more flexible for in situ U‐Th‐Pb analysis.