Comparaison des activités des isotopes de l'uranium et du radium dans quelques échantillons d'eau de puits et de sources thermales au Maroc

Les activités des isotopes de l'uranium et du radium (234U,238U,226Ra,228Ra) ainsi que les rapports d'activité (234U/238U,226Ra/238U,228 Ra/226Ra) ont été mesurés, pour la première fois au Maroc, dans 15 échantillons d'eau de puits et 12 échantillons d'eau de sources thermales. Les résultats obtenus montrent que, contrairement aux eaux de puits, les eaux des sources thermales présentent des activités de238U relativement faibles et des activités de226Ra et des rapports234U/238U élevés. Les activités de l'uranium et du radium mesurées sont comparables à celles que l'on trouve habituellement dans d'autres régions non polluées du monde, elles sont inférieures aux limites maximales admissibles ce qui ne pose aucun risque pour la santé publique au Maroc.Activities and activity ratios of uranium and radium isotopes (234U,238U,226Ra,228Ra,234U/238U,226Ra/238U,228Ra/226Ra) have been determined, for the first time in Morocco, for 15 well water samples and 12 spring water samples. The obtained results show that, unlike well waters, the thermal spring waters present relatively low 238U activities and elevated226Ra activities and 234U/238U activity ratios. Uranium and radium activities are similar to those published for other non polluting regions of the world, they are inferior to the Maximum Contaminant Levels and don't present any risk for public health in Morocco

Slip rate on the Dead Sea transform fault in northern Araba valley (Jordan)

The Araba valley lies between the southern tip of the Dead Sea and the Gulf of Aqaba. This depression, blanketed with alluvial and lacustrine deposits, is cut along its entire length by the Dead Sea fault. In many places the fault is well defined by scarps, and evidence for left-lateral strike-slip faulting is abundant. The slip rate on the fault can be constrained from dated geomorphic features displaced by the fault. A large fan at the mouth of Wadi Dahal has been displaced by about 500 m since the bulk of the fanglomerates were deposited 77–140 kyr ago, as dated from cosmogenic isotope analysis (^(10)Be in chert) of pebbles collected on the fan surface and from the age of transgressive lacustrine sediments capping the fan. Holocene alluvial surfaces are also clearly offset. By correlation with similar surfaces along the Dead Sea lake margin, we propose a chronology for their emplacement. Taken together, our observations suggest an average slip rate over the Late Pleistocene of between 2 and 6 mm yr^(−1), with a preferred value of 4 mm yr^(−1). This slip rate is shown to be consistent with other constraints on the kinematics of the Arabian plate, assuming a rotation rate of about 0.396° Myr^(−1) around a pole at 31.1°N, 26.7°E relative to Africa

Lingulodinium machaerophorum expansion over the last centuries in the Caspian Sea reflects global warming

This article is made available through the Brunel Open Access Publishing Fund. Copyright @ Author(s) 2012. This work is distributed under the Creative Commons Attribution 3.0 License.We analysed dinoflagellate cyst assemblages in four short sediment cores, two of them dated by radionuclides, taken in the south basin of the Caspian Sea. The interpretation of the four sequences is supported by a collection of 27 lagoonal or marine surface sediment samples. A sharp increase in the biomass of the dinocyst occurs after 1967, especially owing to Lingulodinium machaerophorum. Considering nine other cores covering parts or the whole of Holocene, this species started to develop in the Caspian Sea only during the last three millennia. By analysing instrumental data and collating existing reconstructions of sea level changes over the last few millennia, we show that the main forcing of the increase of L. machaerophorum percentages and of the recent dinocyst abundance is global climate change, especially sea surface temperature increase. Sea level fluctuations likely have a minor impact. We argue that the Caspian Sea has entered the Anthropocene

Sedimentological analysis of marine Pleistocene deposits of southeastern Tunisia: evidence of two positive eustatic pulsations during the marine isotopic substage 5e (Eemian, Tyrrhenian)

International audienceAbstract Detailed sedimentological and petrographic analysis of marine Pleistocene deposits along the coastal area of southeastern Tunisia allow to identify two distinct lithostratigraphic units separated by an erosion surface (fig. 2 et 5 A and B). These two commonly superposed units form a ridge parallel to the coast. The palaeocoastal morphology was more irregular than the present-day coastline with areas either more protected or more exposed than now (fig. 3). The lower unit overlies an erosion surface cutting into Mio-Pliocene and Villafranchian deposits. It consists of fine-grained bioclastic quartz-rich sands (fig. 5 C), locally overlain by thin marl layers containing benthic foraminifera and ostracods. The very fine facies (silts and clays) represent relatively protected areas while the coarser facies developed in the more exposed zones. These deposits locally display a well-developed aeolian facies that terminates the sedimentary sequence. This unit, well developed in Jerba Island and Jorf peninsula, strongly resembles the stratigraphic unit of “Khnis” as defined by Mahmoudi [1988] on the coast of Central Tunisia. The upper unit is the better developed in the studied area. It consists of carbonate deposits composed mainly by ooids and peloids (fig. 5 D) and contains also a warm Senegalese fauna, especially Strombus. Locally, in the exposed areas, it shows a coarse facies which resulted mainly from the erosion of the calcareous Villafranchian deposits. This unit displays a remarkable shallowing-upward sequence from shoreface to aeolian dunes (fig. 5 E and F). It constitutes the lateral equivalent of the stratigraphic unit of “Réjiche” as defined by Mahmoudi [1988] in Central Tunisia. These two units, called in this study “quartz-rich unit” (the lower sequence) and “carbonate unit” (the upper one), developed during two distinctive sedimentation phases associated with two sea-level highstands separated by a marine regression. During the first highstand sea-level was about 3 m higher than today whereas it was at about +5 m during the second highstand [Jedoui, 2000]. Along the Mediterranean coasts the Strombus paleobeaches, which are contemporary with the carbonate unit, are well developed and traditionally called Tyrrhenian deposits. Their radiochemical dating, using corals, gives ages of about 125 ka [Hearty et al., 1986 ; Miller et al., 1986 ; Dumas et al., 1991 ; Vai et Pasini, 1996]. We obtained the most reliable uranium/thorium dates in southeastern Tunisia on oyster shells. Results show that the two units developed during the marine isotopic substage 5e [last interglacial ; Jedoui, 2000]. This evidence suggests that substage 5e was characterised by at least two eustatic maxima separated by a lowering of sea level during a marine regression. Our results are therefore in agreement with recent palaeoclimatic reconstructions and in particular with sea level reconstructions and marine oxygen isotope records that indicate the distinct possibility of two positive eustatic pulsations during the last interglacial [Hillaire-Marcel et al., 1996 ; Kindler et al., 1997 ; Plaziat et al., 1998]. Variations in the petrographic content of the two outlined units reflect drastic palaeoclimatic fluctuations in southeastern Tunisia during the last interglacial. The establishment of wetter climatic conditions at the beginning of marine isotopic substage 5e than today was responsible for an enhanced terrigenous materiel supply from the continent as showed by siliciclastic sedimentation along the coast (lower unit). Our data are in agreement with the strong sea surface salinity lowering observed in Mediterranean basins at the beginning of the last interglacial period [Kallel et al., 2000]. The regression of these conditions during the second half of the last interglacial favoured a carbonate sedimentation (upper unit) in southeastern Tunisia

Optegnelser af presten Oluf Bentsen Mandal for aarene 1625-36.

Anthropogenic radionuclide inputs in the Loire estuary (French Atlantic coast) consist of radioactive releases from 14 nuclear reactors located along the Loire river basin, and of fallout from nuclear weapon tests and from the Tchernobyl accident. To estimate to what extent radionuclides associated with sediment accumulate in the estuary, three complementary approaches were used: field surveys, laboratory experiments and numerical modelling. Sampling of bottom sediments, water and suspended solids was carried out at 8 different dates over a 15 month-period. Analysis covered 14C, 90Sr, 3H, the naturally occurring gamma-emitters (uranium and thorium decay chains, 7Be and 40K), and the artificial gamma emitters (mainly cobalt and cesium isotopes). To gain information on the contamination history of the estuary, sediment cores were also collected at different locations inside and outside the estuarine zone. Processes of radionuclide transport and exchange between dissolved and particulate phases were included in a previously developed estuary specific 2D-hydrodynamic model. Equations of sorption and desorption kinetics were derived from laboratory experiments conducted at different salinities. Simulations carried out for two river discharge conditions (low summer flow, high winter flow) allowed to follow radionuclide desorption in the estuary. For long term simulations, a simplified model was developed. It provided estimates of the amount of radionuclides expelled out of the estuary under dissolved and particulate forms, of the transit time for both forms and of the variations in radionuclides concentrations in the fluid mud. Based on computed results and observations, contributions from different origins (natural, military, industrial, marine, continental) to the inventory of radioactivity in the estuary are presented

Study of 2b-decay of Mo-100 and Se-82 using the NEMO3 detector

After analysis of 5797 h of data from the detector NEMO3, new limits on neutrinoless double beta decay of Mo-100 (T_{1/2} > 3.1 10^{23} y, 90% CL) and Se-82 (T_{1/2} > 1.4 10^{23} y, 90% CL) have been obtained. The corresponding limits on the effective majorana neutrino mass are: m < (0.8-1.2) eV and m < (1.5-3.1) eV, respectively. Also the limits on double-beta decay with Majoron emission are: T_{1/2} > 1.4 10^{22} y (90% CL) for Mo-100 and T_{1/2}> 1.2 10^{22} y (90%CL) for Se-82. Corresponding bounds on the Majoron-neutrino coupling constant are g < (0.5-0.9) 10^{-4} and < (0.7-1.6) 10^{-4}. Two-neutrino 2b-decay half-lives have been measured with a high accuracy, T_{1/2} Mo-100 = [7.68 +- 0.02(stat) +- 0.54(syst) ] 10^{18} y and T_{1/2} Se-82 = [10.3 +- 0.3(stat) +- 0.7(syst) ] 10^{19} y.Comment: 5 pages, 4 figure

Study of 2 beta-decay of Mo-100 and Se-82 using the NEMO3 detector

After analysis of 5797 h of data from the detector NEMO3, new limits on neutrinoless double beta decay of Mo-100 (T-1/2 > 3.1 x 10(23) y, 90% CL) and Se-82 (T-1/2 > 1.4 x 10(23) y, 90% CL) have been obtained. The corresponding limits on the effective majorana neutrino mass are: 1.4 x 10(22) y (90% CL) for Mo-100 and T-1/2 > 1.2 x 10(22) y (90% CL) for Se-82. Corresponding bounds on the Majoron-neutrino coupling constant are < (0.5-0.9) x 10(- 4) and <(0.7-1.6) x 10(- 4). Two-neutrino 2beta-decay half-lives have been measured with a high accuracy, (T1/2Mo)-Mo-100 = [7.68 +/- 0.02(stat) +/- 0.54(syst)] x 10(18) y and (T1/2Se)-Se-82 = [10.3 +/- 0.3(stat) +/- 0.7(syst)] x 10(19) y. (C) 2004 MAIK "Nauka/Interperiodica"

Possible background reductions in double beta decay experiments

The background induced by radioactive impurities of $^{208}\rm Tl$ and $^{214}\rm Bi$ in the source of the double beta experiment NEMO-3 has been investigated. New methods of data analysis which decrease the background from the above mentioned contamination are identified. The techniques can also be applied to other double beta decay experiments capable of measuring independently the energies of the two electrons.Comment: 15 pages, 13 figures, accepted in the Nuclear Instruments and Methods