Conventional X-ray Fluorescence Research Articles

Elemental analysis of hourly collected air filters with X-ray fluorescence under grazing incidence.

The X-ray fluorescence under grazing incidence condition (XRF-UGI) was applied for the direct analysis of aerosol filters. Particulate matter less than 2.5 microns (PM2.5) was collected hourly on polytetrafluoroethylene filters using a continuous PM monitor with a virtual impactor method. Although the sampling mass is in trace amounts of 5-30μg, the metallic contents, such as V, Cr, Mn, Fe, Zn, and Pb, can be measured at sub-ng m-3 detection limits. The effects of the non-uniformity and poor flatness of the PM filters were discussed with regard to the measurement repeatability. The relationship between the XRF-UGI intensities and the mass concentrations obtained via conventional X-ray fluorescence (XRF) analysis was confirmed using the fundamental parameter method. Finally, quantification was successfully demonstrated using the XRF-UGI results with the relative sensitivity factors.

Elemental composition x-ray fluorescence analysis with a TES-based high-resolution x-ray spectrometer

The accurate analysis of the elemental composition plays a crucial role in the research of functional materials. The emitting characteristic x-ray fluorescence (XRF) photons can be used for precisely discriminating the specified element. The detection accuracy of conventional XRF methodology using semiconductor detector is limited by the energy resolution, thus posing a challenge in accurately scaling the actual energy of each XRF photon. We adopt a novel high-resolution x-ray spectrometer based on the superconducting transition-edge sensor (TES) for the XRF spectroscopy measurement of different elements. Properties including high energy resolution, high detection efficiency and precise linearity of the new spectrometer will bring significant benefits in analyzing elemental composition via XRF. In this paper, we study the L-edge emission line profiles of three adjacent rare earth elements with the evenly mixed sample of their oxide components: terbium, dysprosium and holmium. Two orders of magnitude better energy resolution are obtained compared to a commercial silicon drift detector. With this TES-based spectrometer, the spectral lines overlapped or interfered by background can be clearly distinguished, thus making the chemical component analysis more accurate and quantitative. A database of coefficient values for the line strength of the spectrum can then be constructed thereafter. Equipped with the novel XRF spectrometer and an established coefficient database, a direct analysis of the composition proportion of a certain element in an unknown sample can be achieved with high accuracy.

Low-radiation dose XRF excited by MeV protons for cultural heritage samples

In this work, we tested a setup of X-ray fluorescence (XRF) excited by proton-induced quasi-monochromatic X-rays (proton-induced XRF (PIXRF)) as a low-radiation dose analytical technique for precious cultural heritage samples. The low-dose performance of the PIXRF is experimentally assessed in comparison with the performance of a conventional XRF. For this assessment, we prepared test samples, which simulated original Japanese paintings with copper-bearing pigments. By introducing a figure-of-merit, the PIXRF is found to potentially give a better performance in terms of the radiation dose to the sample and the limit of detection, albeit the degraded multi-elemental analytical capability. PIXRF can be a cost-effective method to perform low dose measurements of precious samples, if introduced in an existing PIXE facility.

APPLICATION OF TOTAL-REFLECTION X-RAY FLUORESCENCE SPECTROMETRY (TXRF) TO GEOLOGICAL OBJECTS: EXPERIENCE OF THE TXRF LABORATORY, CENTER FOR GEODYNAMICS AND GEOCHRONOLOGY

Unlike conventional X-ray fluorescence spectrometry, the total-reflection X-ray fluorescence spectrometry is not a widespread and routine method for analyzing solid samples with mineral matrix, but it has a great potential for geochemical, geological, and archaeological studies. Rapid multi-elemental analysis of very small sample amounts can be performed by the internal standard method which does not require the matrix-matched reference materials. This is an undoubted advantage of the TXRF method over the conventional X-ray fluorescence method, especially if there is a limited available sample amount and a lack of well-characterized reference materials. This paper presents our experience with the application of TXRF spectrometry in the elemental analysis of apatite, ceramics, sediments, ores, and nodules. Special attention has been paid to the sample preparation procedure because it is one of the main sources of errors in the analysis. Preparing thin homogeneous specimen from the solid sample with a complex mineral matrix is not easy. Sample preparation strategy should be chosen considering the features of an analytical object, the content of the elements to be determined, and the accuracy required for a reliable interpretation. Consideration is being given to the examples of the preparation of a suspension for rapid analysis of ores and sediments, and to the original techniques of chemical decomposition for apatite and ceramics.

µXRF Application for Uranium Exploration (Case Study: Mamuju Deposit, Indonesia)

Micro X-ray fluorescence (µXRF) is an advanced analysis technique from conventional XRF (X-Ray Fluorescence) that allows analysis of smaller areas even inclusions with irregular shapes and non-homogeneous elements. This method has a spatial resolution up to 10 µm depends on the energy by X-rays so that the excitation beam at the smallest point of the sample surface can be detected. This study explains the application of µXRF to determine the type of deposit and the formation of uranium contained in Takandeang Village, Tapalang District, Mamuju Regency, West Sulawesi. The study began with surface geological and radiometry mapping, continued with geological drilling. Collected samples then undergo petrology, petrographic, and geochemical analysis. Three collected samples from drilling sample were analysed using the µXRF. From the analyses we found that the highest uranium anomaly is found in leucitite autobreccias. The anomaly that occurred in the study area was in the form of reconcentration of uranium elements in autobreccia rocks caused by hydrothermal activity which was also supported by magma type and structural control in the study area. In this study case we found that µXRF is usefull for uranium exploration.

Lake-Level Changes and Their Paleo-Climatic Implications at the MIS12 Lower Paleolithic (Middle Pleistocene) Site Marathousa 1, Greece

Lithics and cut-marked mammal bones, excavated from the paleo-lake Marathousa 1 (MAR-1) sediments in the Megalopolis Basin, southern Greece, indicate traces of hominin activity occurring along a paleo-shoreline ca. 444,000 years (444 ka) ago. However, the local environment and climatic conditions promoting hominin activity in the area during the MIS12 glacial remain largely unknown. In order to reconstruct the paleo-environment including paleo-lake levels and governing paleo-climatic factors on a high temporal resolution, we analyzed a 6-meter-long sediment sequence from the archeological site MAR-1 and a Bayesian age model was computed for a better age constrain of the different sedimentary units. A multiproxy approach was applied using ostracods, sponge spicules, diatoms, grain sizes, total organic carbon, total inorganic carbon and conventional X-ray fluorescence analysis. The results from the site represent a protected region surrounded by high mountains under the constant influence of water, either as a shallow partly anoxic water body surrounded by reed belts (>463–457 ka, <434–427 ka), a riverine-lake deltaic system (∼457–448 ka), a floodplain (∼448–444 ka) or a seasonal freshwater pond (∼444–436 ka). The local changes of water levels resemble large trends and rhythms of regional records from the Mediterranean and appear to directly respond to sea surface temperature (SST) changes of the North Atlantic. In particular, when the SSTs are high, more moisture reaches the study area and vice versa. Additional water reaches MAR-1 through melting of the surrounding glaciers after brief warm phases during MIS12 in the Mediterranean realm, which leads to the formation of smaller fresh water ponds, where also the horizon of the excavated remains is placed. Such ponds, rich in ostracods and other microorganisms, provided mammals and humans valuable resources, such as potable water, a wide range of plant species and hunting opportunities. These deposits therefore bear a high archeological potential. The results from our study suggest that the Megalopolis Basin could have served as a refugium for hominins and other organisms due to its capacity to retain freshwater bodies during glacial and interglacial periods.

Fundamental research for a new confocal line X‐ray spectrometer

Confocal X‐ray fluorescence (XRF) spectrometry can be used to perform three‐dimensional elemental analysis, which is impossible using general micro XRF spectrometry without any collimating optics in the detection channel. In this study, we designed, for the first time, a new confocal line XRF (C‐L‐XRF) system that can obtain elemental information of a larger area and higher intensity in XRF analysis than conventional confocal point XRF (C‐P‐XRF) analysis. We evaluate the basic performance of C‐L‐XRF, such as XRF intensity and horizontal and depth spatial resolutions. We identified that the spatial resolution of C‐L‐XRF in the horizontal and depth directions is approximately 2.9 and 2.6 times those of conventional C‐P‐XRF. However, it is possible to obtain an XRF intensity that is approximately 33 times higher than C‐P‐XRF intensity. C‐L‐XRF is expected to be effective for analyzing wide‐area samples such as layered samples.

Monsoon variations inferred from high-resolution geochemical records of the Linxia loess/paleosol sequence, western Chinese Loess Plateau

Chinese eolian deposits have been investigated intensively to reconstruct East Asian monsoon changes at tectonic to millennial timescales. However, high-resolution elemental proxies sensitive to rapid monsoon changes remains sparse. Here we present multiple elemental ratios of the Linxia loess sequence generated by scanning and conventional X-ray fluorescence (XRF) to assess East Asian monsoon variability at glacial-interglacial to sub-orbital timescales. The results show that 11 elements (Al, Si, K, Ca, Ti, Mn, Fe, Rb, Sr, Zr and Ba) can be reliably measured by XRF scanning of loess cores, albeit with relatively lower precision and increased noise levels (due to variable water content and matrix effects) when compared to XRF scanning of dry and homogenized powder samples. Seven elements (Ca, Fe, Ti, Mn, Zr, Rb and Sr), measured by XRF scanning of the core face and powder samples show high correlation (R2 > 0.7, n = 100) with those measured by conventional XRF methods, and thus can be considered as robust indicators for chemical weathering and grain-size sorting. We employ element ratios of Ca/Ti and Rb/Sr to reflect precipitation-induced weathering intensity, and the Zr/Rb ratio and mean grain size to infer the sorting effects related to winter-monsoon winds. These element ratios exhibit significant glacial-interglacial fluctuations, similar to records of magnetic susceptibility and mean grain size. Precessional- to millennial-scale monsoon changes are also persistent in our high-resolution elemental proxies, consistent with those in Gulang loess elemental ratios and Hulu/Sanbao speleothem δ18O records. Our results suggest that high resolution XRF scanning elemental ratios of Chinese loess have great potential for evaluating co-evolution of orbital- and millennial-scale monsoon variations.

Dynamic performance of a fungal biofilter packed with perlite for the abatement of hexane polluted gas streams using SIFT-MS and packing characterization with advanced X-ray spectroscopy

The use of Fusarium solani fungi in an expanded perlite packed biofilter was investigated for the treatment of a hexane polluted waste gas stream using selected ion flow tube mass spectrometry (SIFT-MS). The latter analytical technique proved to be of utmost importance to evaluate the performance of the biofilter at high time resolution (seconds) under various transient conditions, analogous to industrial situations.The biofilter was operational for 277 days with inlet loads varying between 1 and 14 g m−3 h−1 and applying an empty bed residence time of 116 s. The results showed a positive behaviour of the biofilter against different types of disruptions such as: (i) changes in the relative humidity of the inlet gas, (ii) stopping the carbon supply for 1, 5 and 10 days, (iii) varying the inlet hexane concentration (step increases and intermittent pulses) and (iv) limiting the availability of nutrients.X-ray imaging (both conventional 2D μCT and X-ray fluorescence, XRF) was applied for the first time on biofilter media in order to get insight in the internal structure of expanded perlite and to visualise the biomass growth. The latter in combination with online porosity measurements using SIFT-MS provides fundamental information regarding the biofiltration process.

The quantitative analysis of several metal elements in a solution by the confocal X-ray fluorescence thin-sample approach

By a comprehensive combination of confocal X-ray fluorescence and thin-sample approach used in conventional X-ray fluorescence devices, a new “confocal equivalent thin-sample method” based on confocal X-ray fluorescence setup is proposed. It is used to quantify the concentration of several metal elements in a solution. Compared with the conventional X-ray fluorescence, this method could quantify the sample directly via the thin-sample approach and required not complicated sample preparing process. In the study, a liquid solution containing Cr, Mn, Fe, Co, Cu, Zn, As, Br, and Sr wase used to verify the proposed method.

Comparison and correction of element measurements using qualitative and quantitative X-ray fluorescence in lacustrine sediments: A case study of Lake Hurleg

Using an X-ray Fluorescence (XRF) core scanner with nondestructive and successive, the chemistry features of lacustrine sediment can be measured directly. This method of XRF core scanner measurements has been widely applied to core sediment analysis but uncertain of the precision and accuracy. Comparison of intensities obtained by XRF core scanning and the concentration measured by conventional X-ray Fluorescence, indicates effects of physical properties varied from different elements on elemental intensities in the lacustrine sediments of a core from Lake Hurleg in the northeastern Tibetan Plateau. Correlation among elements Ti and Sr between the two measurement methods of the XRF and the conventional XRF is high. Using the intensity of Cl as an indicator of water content, the element intensities of Ti and Sr in the core samples is corrected. But the correlation coefficients of Ti and Sr is litter raised. The results show that XRF core scanning is a very useful tool for measuring element concentration in sediments particularly for high intensities elements.

A simple and sustainable portable triaxial energy dispersive X-ray fluorescence method for in situ multielemental analysis of mining water samples

In-situ monitoring of potentially toxic elements in mining water samples is of special relevance in order to evaluate the environmental impact of abandoned mining activities. However, it is difficult to develop suitable analytical methods for this purpose considering the complexity of mining water samples matrix as well as the limited sensibility of conventional filed portable X-ray fluorescence spectrometry systems (pXRF).In the present contribution, a simple, sustainable and reliable triaxial pXRF method (3pXRF) is proposed for multielemental analysis of mining water samples. In this method, several microliters of sample are deposited onto a commercial filter paper retainer and after drying, the loaded filter is directly analyzed in the field using a laboratory pXRF with orthogonal triaxial geometry (p3XRF). This geometry reduces the background of the measured spectra improving peak-background ratios in comparison with conventional pXRF systems.Using the best analytical conditions (sample deposition volume of 200 μL and 600 s as measurement time), limits of detections were in the low mg∙L−1 range and therefore suitable considering the expected high metal concentration in mining water samples. Acceptable accuracy and precision of the results was obtained in comparison with laboratory techniques such as inductively coupled plasma optical emission spectrometry and total reflection X-ray fluorescence spectrometry but with the possibility of in-situ measurements in the field. The developed method was applied to the analysis of different types of mine water samples (stream waters, drainage water tanks and mining lake waters) collected in the mining districts of Tinoca (Portugal) and Cartagena-La Unión (Spain).

A new XRF spectrometer using a crystal monochromator and parallel plates beam guides

Conventional x-ray fluorescence analysis (XRF) is a powerful instrumental technique for elemental quantification of samples with a wide range of matrices coming from industry, medicine, biology, environmental and archaeometry. The scattering of the x-ray tube excitation beam from the matrix is mainly responsible of the strong background in XRF spectra which restricts the detection limit (DL) to a few ppm (w/w). One possible strategy to reduce the DL is the monochromatization of the excitation beam with a crystal monochromator. In this case, the optimization of the system components is strongly required to obtain the highest excitation count rate over the sample, since it is considerable reduced by the short energy band pass of the monochromator.In the present work an optical device composed by a Si(100) crystal monochromator and two parallel plates beam guides (PPBG) was characterized and including in a conventional XRF spectrometer to improve the DLs. The PPBGs are composed by several thin glass plate reflectors placed together and separated by spacers. Inside the gap, x-rays are transmitted by total reflection contributing to the photon flux at the output of the optical device. The first PPBG reduces the divergence of the beam striking the crystal, and the second one collects the monochromatic beam that emerges from the crystal. In this way, the design of the optical device is quite compact keeping a high photon flux at the output thanks to the wide acceptance solid angle of the PPBGs. The new XRF spectrometer was applied to the analysis of biological tissues. The first results obtained in this field are shown in the present work where the performance of the spectrometer can be evaluated.

X-ray fluorescence scanning of discrete samples – An economical perspective

We measured discrete, powdered, homogenized samples from geochemical reference standards (GRS) and from a loess-paleosol sequence (LPS) with an ITRAX XRF core-scanner. The objective is to highlight cost- and time-efficiency of X-ray fluorescence (XRF) scanning of discrete samples in comparison to conventional XRF. Based on data precision (mainly < 4% mean relative standard deviation) and data reliability (often R2 ≥ 0.9) tests with six different measurement times (1, 5, 10, 30, 60 and 100 s) and two different X-ray tubes (Mo, Cr), reasonable minimal measurement times for thirteen considered elements were assessed. Accordingly, we designed test case scenarios for 10, 30 and 100 s measurement time in comparison to conventional XRF analysis with regard to cost- and time-efficiency.As long as qualitative geochemical data are sufficient for scientific research questions at hand, XRF scanning of discrete samples is proven to be more efficient by factors of 15–23 as to time and by factors of 4.5–51 as to cost when compared with conventional wavelength-dispersive (WD)-XRF analysis commonly applied to discrete samples. This underlines XRF scanning of discrete samples as a versatile, non-destructive qualitative geochemical screening tool with unprecedented time- and cost-efficiency. Such efficiency will foster application of this technique in a broad scientific field including e.g. terrestrial paleoenvironmental reconstructions and/or environmental pollution studies.

Observation of Au[sbnd]Cu alloying by grazing-incidence X-ray fluorescence

Alloying between AuCu binary thin layers was observed by grazing-incidence X-ray fluorescence (GI-XRF) technique using a benchtop total-reflection XRF instrument with a Mo-Kα-excited X-ray beam. The as-deposited sample comprising Au and Cu layers deposited on a glass substrate and a corresponding sample heated at 300 °C for 1 h were analyzed by GI-XRF. The angle-dependent GI-XRF profile of the heated sample differed from that of the as-deposited sample. Theoretical calculations of the GI-XRF profiles of the as-deposited and heated samples suggested that alloying occurred at the low temperature of 300 °C. The same samples were further independently investigated using other non-destructive X-ray methods, including X-ray diffraction (XRD), X-ray reflectometry (XRR), and conventional X-ray fluorescence (XRF). The results obtained by the XRD, XRR, and XRF analyses were in good agreement with the GI-XRF results.

Feasibility of the use of a handheld XRF analyzer to measure skin iron to monitor iron levels in critical organs

There exists a need for accurate, non-invasive point-of-care tests to detect body iron burden. This study investigated the use of x-ray fluorescence (XRF) measurements of skin iron as a marker for organ iron content in rats. This study also evaluated a novel application of a commercial XRF device, commonly used in mining and construction, as a rapid, portable, and non-invasive measurement tool. Rats (n = 32) were loaded with iron dextran and the iron signal of each animal’s skin, liver, and kidney was measured using a conventional XRF system. A quadratic correlation was observed between liver and skin iron signal (R2 = 0.92) and a linear correlation was observed between kidney and skin iron signal (R2 = 0.65). As such, it is concluded that skin iron content can act as a marker for both liver and kidney iron content. The same skin samples were measured using the portable XRF device and compared to the liver and kidney samples measured in the conventional XRF system. Again, a quadratic correlation was observed between liver and skin iron signal (R2 = 0.91) and a linear correlation was observed between kidney and skin iron signal (R2 = 0.83). Thus, the portable XRF device can provide rapid non-invasive, skin XRF measurements. Dosimetry was performed using the portable XRF device to assess the radiological hazard associated with its use. The average skin equivalent dose from this device is 30 ± 10 mSv/min, when the device is collimated and operated at 40 kV. In conclusion, skin iron XRF measurements can act as a surrogate marker for liver iron content, and can be measured using a commercial XRF device for a portable, fast, and non-invasive measurement.

Improving grade control efficiency with rapid on-line elemental analysis

Flotation circuit control is typically based on regular on-line elemental analyses. In base metal applications the conventional assaying method is X-ray fluorescence (XRF), which has proven to be a reliable and accurate technology. However, in large flotation plants with many sample streams to be analyzed, the measurement frequency for individual assays decreases because a centralized XRF analyzer can only measure one stream at a time. This results in unnecessary delays that reduce the control performance. Nevertheless, by integrating reflectance spectroscopy measurement with the conventional XRF technology, a practically continuous assay can be obtained. In this paper the advantages of improved analysis cycle to process performance via faster automated higher level flotation circuit control are demonstrated. The presented technology enables capturing and reacting to grade fluctuations that may have been missed with longer measurement intervals. Moreover, response time to drastic changes in flotation circuit operation is significantly reduced which results in better process performance.

Using Scattered Radiation Method in element analysis of sediments by total reflection X-ray fluorescence

A technique for determining Al, K, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Rb, Sr and Ba in sediments by total reflection X-ray fluorescence (TXRF) was proposed. Sample preparation procedure consisting of suspending 20 mg of powdered sample in 2 ml of a 0.5% methylcellulose solution and depositing a volume 10 µL of a slurry on the reflector showed to be the most suitable. The sample preparation error did not exceed 10% for most analytes. In order to calculate the concentration of the elements, scattered radiation method was used where the analytical parameter was the ratio between the intensity of the analytical line and the intensity of the scattered incoherent radiation of the MoKα line. Using the intensity of the scattered incoherent radiation allowed taking into the account the variations in the surface density of the dried sample on the reflector. To control accuracy, certified “BIL-1” and “SGH-1” reference materials were used. It was shown that the scattered radiation method does not concede with the internal standard method widely used in TXRF and provides better results than the internal standard method in most cases. The TXRF results obtained for the sediment samples were compared to the results obtained by a conventional X-ray fluorescence spectrometer. It was shown that the changes in the element content along with the core depth obtained by both methods, were consistent and had a common tendency. Key words : X-ray fluorescence analysis, XRF, total reflection X-ray fluorescence, TXRF, sediments, methylcellulose, internal standard, scattered radiation method (Russian) DOI: http://dx.doi.org/10.15826/analitika.2018.22.2.004 G.V. Pashkova 1,2 , М . М . Mukhamedova 1,2 , Т .S. Aisueva 3 , А .L. Finkelshtein 1,3 , А . А . Shchetnikov 1,4 1 Institute of the Earth’s Crust, SB RAS, Lermontov st., 128, Irkutsk, 664033, Russian Federation 2 Irkutsk State University,1 K. Marx St., Irkutsk, 664003, Russian Federation 3 Vinogradov Institute of Geochemistry, SB RAS, Favorsky st., 1A, Irkutsk , 664033, Russian Federation 4 Irkutsk Scientific Center, SB RAS, Lermontov st., 134, Irkutsk, 664033, Russian Federation

A sample carrier for measuring discrete powdered samples with an ITRAX XRF core scanner

The elemental composition of discrete powdered sediment samples can be measured by the energy‐dispersive X‐ray fluorescence (XRF) system that is installed in XRF core scanners. Because an appropriate sample carrier for powdered samples is currently not available, for example, for the ITRAX XRF core scanner, such a carrier is presented in this technical note. The designed sample carrier can hold 30 sample cups with a volume of 0.88 cm3 each. A maximum of 5 sample carriers, that is, 150 samples, can be measured in one run. The sample cups and carriers are optimized for a measurement procedure with a step size of 5 mm and variable count times up to 100 s per sample. With this setting, data are collected from an area of 100 mm2 in the center of the sample thereby ensuring a good representativeness of the signal because potential sample inhomogeneity is accounted for. Because the described sample carrier system allows rapid element analyses of discrete powdered environmental samples with an XRF core scanner, it may in some cases represent a time‐ and cost‐efficient alternative to conventional XRF analyses.

A 3 million year index for North African humidity/aridity and the implication of potential pan-African Humid periods

Mediterranean sediments are valuable archives of both African monsoon variability and higher-latitude climate processes, and can also be used to provide an environmental context for early human migrations and settlements. However, the long history of Mediterranean palaeoclimate studies largely pre-dates the advent of widespread x-ray fluorescence (XRF) core-scanning, so there are few continuous and high-resolution geochemical records from this key region that extend beyond the last glacial cycle. Here we present XRF core-scanning results for ODP Site 967 (Eastern Mediterranean) that have been fully-calibrated into element concentrations spanning the last 3 million years (My). Comparison with independent geochemical data from conventional XRF highlights disparities for certain element/element ratios, thus suggesting the need for caution when taking ratios of scanning XRF data. Principal component analysis of the calibrated XRF dataset reveals two dominant components: detrital inputs (PC1) and a ‘sapropel’ (≈monsoon run-off) signal (PC2), which we use to establish a new orbitally-tuned chronology. We observe inverse covariation between PC2 and a previously published aeolian dust record from ODP Site 967 (Larrasoaña et al., 2003), and combine these records to produce a composite index of humidity and aridity for the wider North African region over the past 3 My. We propose that by combining run-off and dust signals in a single metric, our index captures the effects of both strengthening/northward migration (increased run-off) and weakening/southward retreat (increased dust) of the North African monsoon. Comparison of the index with published records of Northwest and East African palaeohumidity suggests that it tracks the timing of “Green Sahara Periods” throughout the Plio-Pleistocene, and that at least 30 of these intervals coincided with increased humidity across East Africa. We tentatively suggest that these specific episodes may be termed “pan-African Humid Periods”, as a means to highlight large-scale climate trends and to provide an environmental framework for palaeo-anthropological research.