The importance of U-series disequilibrium of sediments in luminescence dating: A case study at the Roc de Marsal Cave (Dordogne,France)

A multidisciplinary study of the Roc de Marsal Cave gave us the opportunity to re-examine the known problem posed by U-series disequilibria in sediments in the field of palaeodosimetric dating. Apart from burnt flints and heated limestones, the material being dated, THAT IS our principal concern here, is made of burnt sediment samples collected from a reddish layer that forms the very base of the Roc de Marsal Mousterian sequence (Couche B). U-series disequilibria of long life nuclides in sediments were observed: as a general trend, the activity of ²³⁸U is greater than that of ²²⁶Ra. Important discrepancies in age determination can occur according to the origin of the disequilibrium and its kinetics. To characterise these ancient modifications of radioactivity and constrain the range of possible variations of annual doses, a statistical study of ²³⁸U, ²²⁶Ra and ²³²Th activities, measured by gamma spectrometry, was carried out. It shows that the sediment was mainly enriched in mobile uranium. This conclusion is in accordance with the results of complementary measurements of ²³⁰Th and ²³⁴U performed by alpha spectrometry. On the kinetics side, two models of time-variation of U and daughter concentrations are compared, taking experimental data into account. A detailed presentation of the methodology and the method of calculation of dose rates, and particularly time-averaged dose rates in such a situation, is given.     

A comparison between neutron-fluence measurements using metal-activation monitors and standard glasses calibrated via thin uranium-fission monitors and via ηq method

The two fundamental approaches to fission-track dating involve either an explicit determination of the thermal neutron fluence (φ-method) or a calibration against age standards (ζ-method). The neutron fluence measurements are carried out with metal-activation monitors or with uranium-fission monitors, co-irradiated with the samples. Uranium-fission monitors consist of either a thin “mono-atomic”) film, or a thick fission source (standard uranium glass) irradiated against a muscovite external track detector. In this work, different techniques for performing neutron-fluence measurements were compared: based on thin-film calibration, based on thick-source calibration, and based on gamma spectrometry of co-irradiated metal monitors (Au, Co). The results suggest that more experiments are needed to make all calibrations consistent, including new measurements of the length of etched induced tracks in mica. Also the standard glass calibration carried out with thin films should be confirmed with a greater number of calibrating irradiations.     

On Dating of Old Groundwater

Groundwater dating is known to be determination of the residence time of groundwater. This residence time is commonly defined as the length of time the water has been isolated from the atmosphere. The paper reviews isotope methods available for dating of old groundwater. Their residence time is supposed to be far outside the range of C-14 dating which is about 50000 years. These dating methods are based on the radioactive decay of long-lived radionuclides produced by interaction of cosmic radiation with gases in the atmosphere (Kr-81, Cl-36, I-129), on the accumulation of noble gases suo-surface produced by nuclear reactions including radioactive decay of U/Th series radionuclides (He-4, He-3), and on the disequilibrium between uranium isotopes due to water-rock interaction and radioactive decay (U-234, U-238). The paper presents the principles of these dating methods, refers to recent case studies and summarizes problem areas for further development and application of these methods.     

TL and radiocarbon dating of neolithic sepultures from Sudan: Intercomparison of results

Thermoluminescence dating of a set of 29 pottery sherds excavated at the neolithic sites of El Kadada and El Ghaba (near Shendi, Central Sudan) was carried out at Bordeaux University. The archaeological dose was measured using the fine grain technique. The annual dose was determined by analytical techniques (neutron activation analysis, ICP spectrometry, XRF, low background gamma spectrometry) and by “on-site” measurements of the environmental radioactivity (gammametry). The crystalline inclusions of the samples were characterized by optical microscopy and cathodoluminescence: the TL minerals mainly consist of quartz and K-feldspar crystals. In some cases, radioactive inclusions of zircons and monazites are observed. The TL and the radiocarbon dates show a good agreement, verifying the validity of the radiocarbon ages which were suspected to be too old because of the nature of the dated material (shells). Taking into account all the chronological data, it is shown that El Ghaba and El Ghaba necropolis were used respectively within the 4800-3300 B.C. and 4200-3000 B.C. date-ranges for neolithic cultures, the occupation of El Kadada starting five or six centuries later than El Ghaba.     

Radiation background due to radioactive sources in a luminescence dating laboratory

For practical reasons, usually, luminescence dating laboratories contain in the same room (or in adjacent rooms) the equipment and the radioactive sources, as well as the storage cabinet for the samples. It is generally assumed that the absorbed dose due to ambient radioactivity is null or at least negligible in terms of human health (below the dose limit).To test the actual dose rate inside our laboratory room, an investigation combining portable dose rate meter, portable NaI(Tl) gamma spectrometry, and blue-OSL dosimetry using Al₂O₃:C pellets was made. Although our measurements show the presence of X-rays as far as 3 m from the sources, the dose rates are below the safety regulation and does not affect the dating of the sample stored in the same room as the radioactive sources.     

On the dose-rate estimate of carbonate-rich sediments for trapped charge dating

In a wide range of environmental conditions sediments are subject to changing water content and carbonate cementation during burial. Trapped charge dating of these carbonate-rich deposits requires the determination of a dose rate which is not constant during burial because sediments were subject to post-depositional geochemical alterations. The dose-rate model established in this study assumes linear increase of carbonate mass and linear decrease of water mass in pores between sediment particles during burial. Numerical modelling assesses the effect of carbonate and water on the infinite-matrix dose rate as a function of time. Sensitivity testing of the system indicated that water and carbonate content have the greatest effect on the resulting dose rate, followed by the timing of onset and completion of carbonate formation. As a consequence, a comprehensive re-calculation of the water correction factors was undertaken. It revealed a 5% lower value for the annual beta dose and a 10% lower value for the annual gamma dose compared to values formulated by Zimmerman [1971. Thermoluminescence dating using fine grains from pottery. Archaeometry 13, 29–52].

The dose-rate model was tested using samples from geologically well-constrained coastal sites. The differences between onset and final dose rate were up to 30% resulting in differences between modelled and conventional optical ages between 2% and 15% depending on the final (today's) water and carbonate content. The divergence of dates may be greater under certain conditions. The dose-rate model can be applied to a wide range of contexts similar to those considered in this case study.     

Mineral zircon: A novel thermoluminescence geochronometer

Mineral zircon contains trace amounts (typically 10-1000 v ppm) of the f -emitters uranium and thorium, which irradiate this mineral internally. This outstanding feature of zircon turns out to be extremely useful when this mineral is applied as a thermoluminescence (TL) dating medium, because the build-up of the age-dependent luminescence is dominated by the presence of well-defined internal radioactive sources and the contributions to the dose from external radiation sources are two orders of magnitude smaller. The results presented in this paper have led us to the conclusion that for zircon dating it is necessary to carefully select the best and homogeneous zircon grains of the highest optical quality. For successful dating experiments on very young and historically well-defined coastal dune sands, selection of the most stable luminescence component by means of narrow band interference filters is needed. Our results suggest that ultimately optical zircon dating will allow us to determine the age of extremely young samples ( e.g. 12 months!).     

Gamma and enclosure dosimetry for TL/ESR dating with the new Al2O3: C TL dosemeter

Al₂O₃: C manufactured by LAIKS-CORUND, Ekaterinenburg, Russia, offers several advantages for the measurement of environmental radiation: stability, low self-dose, high sensitivity and energy deposition features under gamma and beta irradiation very similar to quartz and quartz-like TL minerals. In the present work those properties were tested for in situ gamma dosimetry, by comparison with other dosimetric techniques. It was confirmed that this phosphor is very well adapted to this purpose. On the other hand, the new alumina can be made insensitive to external alpha radiation by means of thermal treatments. This α-insensitized alumina is very interesting for enclosure dosimetry in the perspective of quartz inclusion dating. In this technique, the quartz grains to be dated are faithfully simulated by alumina: the phosphor allows us to measure directly the dose that would be experienced by quartz grains (HF etched, as usual). However, because the attenuation of beta radiation by coarse grains must be taken into account in inclusion dating, the role of this factor was theoretically and experimentally—with Al₂O₃—explored. The preliminary experiments indicated that enclosure dosimetry with this new alumina was a promising technique.     

碳酸盐沉积物的ESR断代

本文用ESR断代法测定某些碳酸盐沉积物的年代,其结果与¹⁴法符合得很好。对影响ESR断代法测定精度的一些因素进行了详细的讨论,如样品的处理、ESR测量、数据处理,年剂量和总累积剂量的测定。     

Sediment dating by luminescence: a review

In the present article we review applications of luminescence methods for the determination of the age of sediments for Quaternary Earth science. “Sediment” is taken to include any mineral particles transported by wind, water and/or ice and subsequently deposited. Methodology is not discussed per se but appears in context. The emphasis is on recent work and is illustrative rather than exhaustive. Applications in archaeology are mentioned only briefly. Successful dating requires that the luminescence signal has been zeroed by sunlight at the time the sediment was laid down. Dune sands and loess transported in full daylight usually satisfy this condition and have been dated by both traditional thermoluminescence and by optical methods. Optical dating is advantageous for less well-bleached sediments, such as are found in colder climates and those laid down by fluvial and glacial processes, although the prospects for dating the latter are shown to be poor. Among less common contexts are volcanic eruptions, earthquake faults and tsunami deposits. The dating of very young sediments, less than 2 ka, is demonstrated and the factors limiting the dating of very old sediments, 500 ka to 1 Ma, are discussed. Validation of any dating method by comparison with other methods is necessary; luminescence ages have been successfully compared with ages obtained by, for example, ¹⁴C, U–Th series and δ¹⁸O isotope ratios. The most difficult problems encountered in dating quartz, feldspars and undifferentiated fine grain mixtures include: anomalous fading (which leads to underestimates of age), incomplete zeroing (which gives overestimates) and sample inhomogeneity. Methods devised to minimise these effects include preheating regimes, selection of observing wavelengths and of stimulating wavelengths for optical dating, the use of single aliquot and single grain measurements. The use of appropriate data analysis procedures is also important. Advice on current best practice on procedures for obtaining reliable ages is offered and, in all applications, there are suggestions as to where further research might be directed.     

Fission-track dating of Macusanite glasses with plateau and size correction methods

Two Macusanite pebbles (MB1 and MB2) were dated with the fission-track method. Six irradiations were carried out in different nuclear reactors: Pavia (Italy), IPEN-CNEN (Brazil) and IPEN-Lima (Peru). Measurements of the thorium and uranium induced-fission per target nucleus using natural thorium thin films and natural U-doped glasses calibrated against natural uranium thin films, together with a λ_F of 8.46×10⁻¹⁷ a⁻¹ were used to determine the ages. The apparent ages were corrected using the plateau and size correction methods. Track measurements were performed by different analysts, using different counting criteria. In addition, tracks were measured on samples which had been submitted to thermal treatment as well as on samples which had not been heated. Thermal treatments were carried out to erase the fossil tracks before neutron irradiation. No significant differences have been found in individual results, using the two Macusanite pebbles and the different nuclear reactors, age correction techniques, analysts, track-counting criteria, and thermal treatments before neutron irradiation. The great majority of the results (14/17) is compatible with the Ar–Ar ages of 5.12±0.11 and 5.10±0.11 Ma, Macusanite MB1 and MB2, respectively. However, the fission-track ages are systematically less (8%) than the Ar–Ar ages of the two Macusanite samples studied.     

Beta-gradient isochron dating of thin tooth enamel layers using ESR

The theoretical and experimental basis for the development of a new dating technique using beta-gradient isochrons and ESR is presented. For uranium-free portions of enamel adjacent to sediment, we can determine a beta-dose gradient due to sources in the nearest 2 mm layer of the sediment. If the equivalent dose to successive layers of enamel is plotted against the beta dose rate to each layer, an estimate of the age (equal to the slope of the line) that depends only on the environmental beta dose rate can be determined. Experimental methods and results for four teeth are discussed. The significance of this approach lies in its ability to isolate an age estimate that is independent of the uranium uptake model, since only portions of the enamel which are far away enough from internal sources of uranium, such as dentine, are used. In addition, this technique provides a time-averaged estimate of the actual gamma plus cosmic dose rate provided that a reasonable estimate of the average moisture content is used to calculate the environmental beta dose rate.     

Determination of thorium and uranium contents in soil samples using SSNTD’s passive method

Thorium-to-uranium ratios have been determined in different soil samples using CR-39 and LR-115-II solid-state nuclear track detectors (SSNTDs). A calibration method based on determination of SSNTD registration sensitivity ratio for α-particles of thorium and uranium series has been developed. Thorium and uranium contents of the standard soil samples have been determined and compared with its known values. There is a good agreement between the results of this method and the values of standard samples. The method is simple, inexpensive, non-destructive and has a wide range of applications in environment, building materials and petroleum fields.     

Monte Carlo determinations of the beta dose rate to tooth enamel

The results of Monte Carlo simulations of the beta dose rate to enamel are presented. The dose rates are the most comprehensive to date, incorporating the beta spectrum from 21 different radionuclides, all internal conversion and Auger electrons, the majority of the bremsstrahlung radiation, effects due to radon loss in the uranium series, and variations in the moisture content of the sediment. Applications to a new dating technique in archaeology using electron spin resonance and beta-gradient isochrons are discussed.     

Radioactivity measurement in the granites of North Karnataka, India and its radiological implications

The natural radioactivities due to uranium, thorium and potassium in granite samples contribute to the radiation dose received by human beings significantly. It is essential to evaluate the activity levels of these nuclides for the assessment of natural radiation dose. The natural radioactivity levels of some granite samples collected from different quarries of North Karnataka, India are estimated using high-resolution gamma ray spectrometry technique and the results are reported in this paper.     

Identification of paramagnetic centers and the dating of cave dripstones by electron paramagnetic resonance

Dating of samples of cave dripstones collected from the Jaskinia Czarna (the Polish Tatra Mountains) and fossil bones was carried out by means of electron paramagnetic resonance (EPR). By this method the age of the sample is found as the ratio of the total dose (TD) to the annual dose rate (D _a). TD is established on the basis of EPR spectra, whileD _a is the sum of the internal dose rate, calculated on the basis of the concentration and activity of radioactive nuclides in the sample, and the external dose rate measured at the site of the sample collection by a calibrated γ-radiation probe. Two models of uranium accumulation were used: the model of linear accumulation and the model on the basis of the assumption of a disturbed radiation equilibrium in the uranium series. The results were compared with the age determined by the uranium-thorium method. Moreover, by the computer resolution enhancement method the dynamics of paramagnetic centers in calcite annealed in nitrogen atmosphere was studied in the range of 283–873 K, and the results were compared with earlier results for calcite annealed in the air. On the basis of the study of paramagnetic center dynamics in dripstone calcite it was established that the radicals responsible for the EPR signals were CO₂⁻ in different symmetries of the crystalline field, CO₃³⁻ in the axial symmetry, CO₃⁻ in the axial and isotropic symmetry and HCO₃²⁻. The results implied that samples to be subjected to EPR dating should be kept at room temperature.     

The potential health hazard due to elevated radioactivity in old uranium mines in Dolina Białego,Tatra Mountains,Poland

Natural radioactivity is one of the essential components of the environment. Unlike the Sudety mountains area in Poland, the Tatra Mountains were not the subject of wide survey as regards the levels of natural radioactivity. Especially, the concentrations of radon (natural radioactive gas) have not been investigated there in terms of their possible negative health impact. Within the frame of bilateral cooperation between the Institute of Nuclear Physics in Kraków, Poland, and the Jo?ef Stefan Institute in Ljubljana, Slovenia, the measurements of natural radioactive elements in old uranium mines in the Tatra National Park were performed in June 2010. The investigated sites were located in Dolina Bia?ego (The Valley of the White). One of the mines is situated near the tourist path. The paper presents the results of complex measurements of natural radioactivity in both uranium drifts. The concentration of radon gas inside the mining drifts exceeded 28,000 Bq m^?3. Also, very high gamma dose rates were observed (up to 5600 nSv h^?1). The maximum concentrations of natural radioactive elements (potassium ⁴⁰K, radium ²²⁶Ra, thorium ²³²Th) in rock samples amounted to 535, 2137, and 18 Bq kg^?1, respectively. The effective dose rates due to radon and thoron inhalation have been assessed as 0.013 mSv h^?1 (for the lowest concentration) and 0.121 mSv h^?1 (for the highest concentration).     

Uranium analysis in Cypriot groundwaters by total alpha-radiometry and alpha-spectroscopy

Two different alpha-radiometric methods (e.g. alpha-spectroscopy and alpha-particle counting) have been applied to the determination of uranium in Cypriot groundwater samples after separation of the radionuclides by cation exchange using Chelex-100 and its electrodeposition on stainless steel planchettes. The data obtained were compared to show the advantages and disadvantages of the two radiometric methods, determine the alpha-radioactivity concentration and the radiation dose associated with the use of the studied groundwaters. Calibration of the methods was performed by means of uranium standard solutions and the corresponding data were used to evaluate linear range, detector efficiency, detection limits, value of the information obtained, and time of analysis of the methods. Comparison of the data obtained from calibration and natural sample measurements has shown that alpha-particle counting with a simple alpha-radiometer (equipped with a semiconductor detector) may offer only an activity value and not detailed information about the isotopic composition but it is the fastest method and the method of choice if only a screening method for the alpha-radioactivity measurement is required. Based on the alpha-radioactivity data, the corresponding radiation dose was estimated for situations where the groundwaters are used for drinking water purposes.     

Uranium analysis in some food samples collected from Bathinda area of Punjab, India

To strengthen the radiation protection infrastructure in Bathinda, the uranium concentration in daily diet of the residents has been measured and its associated radiation risks were estimated for the adult population. Food samples were collected from major cancer prone areas of the district, from which daily diets were prepared. These diet samples were analyzed using fission track technique. The measured values of the uranium content were found to vary from 0.38 mBq/g in mustard seeds to 4.60 mBq/g in wheat. In case of milk the uranium content is found to vary from 28.57–213.36 mBq/ℓ with mean concentration of 61.35 mBq/ℓ. This leads to a daily dietary intake of 0.90 Bq/day. The measured value of 0.90 Bq d⁻¹, contributes to 1.12 mSv to the cumulative effective dose to the population. This dose is much large than the International Commission for Radiological Protection (ICRP) annual effective dose limit of 1 mSv for the general public [1]. Therefore, it would pose significant health hazard.      

The use of nuclear prospecting measurements for characterizing the radioactive status of Al-Bayyarat and Sabkhet Mouh areas,southern Palmyrides,Syria

Al-Bayyarat and Sabkhet Mouh areas in southern Palmyride have been radioactively characterized by using different nuclear prospecting measurements. Those measurements include the application of airborne, carborne spectrometric gamma, radon emanation and borehole techniques. The merging of airborne, carborne spectrometric gamma data enables to establish the normalized eU, eTh, and K% maps in the study area. Radon emanation and spectrometric gamma measurements have been applied only in Al- Bayyarat area, where radioactive anomalous zone has been observed. The radioactive characteristics of the study area has been explained through studying and analyzing a profile of 30 Km long, where a plausible geo-radioactive model has been proposed for the uranium leaching and its transport.