U-deposit hosted in hydrothermally altered tuffs in Mexico, together with weathering profiles from Cameroon were studied as natural analogues of radionuclide release and migration. Using petrological and spectroscopic methods (infrared and electron paramagnetic resonance), we have distinguished successive secondary mineral parageneses and the behaviour of radionuclides.
In the U-deposit, the mineral parageneses show that uranium migration is mainly controlled by the redox potential and silica activity of the altering solutions. The high silica content of the solutions is caused by the intense alteration of volcanic rocks. Two types of secondary clay mineral parageneses are evidenced: a kaolinization, intense where uranium is accumulated in the welded tuffs, and a smectitization mainly developed in the underlying weakly welded tuffs.
Several types of kaolinite have been defined according to their genesis (fillings in fissures and feldspar pseudomorphs), their location relative to a breccia pipe where uranium has accumulated (core and rim of the pipe; surrounding rhyolitic tuffs), and particle morphology, structural order and substitutional Fecontent. It is shown that the variations of the concentration of paramagnetic defect centres, always more than ten times as important than those measured in weathering kaolinites, are only correlated to the location of the kaolinites. The highest values correspond to the breccia pipe kaolinites, e.g. kaolinites located in the uranium accumulation zones. Moreover, one or two main defects centres are detected depending on the intimate association of kaolinites with uranium-bearing minerals. Besides, in weathering kaolinites from U-depleted laterites, defect centre concentrations are correlated to the total Fe203 content in bulk samples. This means that the defect centre acts as a memory of the travel of uranium when this element was sorbed onto iron gels in the first stage of weathering.
It is concluded that paramagnetic defect centres in kaolinites might allow an efficient fingerprint of successive irradiations in the natural analogues under study and could be an useful tool to control radionuclides migration through kaolinite-containing clayey materials such as those used for waste repository.
A better understanding of radiation efficiency as well as accurate dose-ratekaolinite-containing clayey materials such as those used for waste reposit estimation are needed for a quantitative tracing of the migration ofA better understanding of radiation efficiency as well as accurate dose-ratekaolin radionuclide elements. With this aim, a simulation has been undertaken withestimation are needed for a quantitative tracing of the migration of various radiations sources. We have determined for each irradiation the parameters of the paramagnetic centres created in order to understand the way they are forming. The knowledge of the parameters governing the formation and the stability of the radiation centres in kaolinites allow to use this mineral as a natural dosimeter. 相似文献
The seismic analysis of a reactor building on a sliding-type base isolation is performed by way of the hybrid frequency-time-domain procedure. The frequency dependence of the foundation stiffness coefficients is duly accounted for in the analysis, although the problem is non-linear. The response results are shown to be reliable by way of comparison with the results of a time-stepping algorithm in the specialized case of constant foundation stiffness coefficients. The fact that such an analysis can be performed is an outstanding result, particularly when considering that no difficulties are encountered in the implementation and in the calculation. The flow chart used to implement the procedure is presented in the paper. The reactor building is analysed for three different sites with each site having three sets of material properties. It appears that the structural response is not strongly affected by the frequency dependence of the foundation stiffness coefficients. This also holds true as far as the response of equipment attached to the superstructure is concerned. For all practical purposes this frequency dependence may be disregarded in favour of constant spring and damping coefficients. 相似文献
Sackungs are the largest gravitational deformation observed in mountains. They are characterized by the long-term slowness of the movements, but their mechanism is still not well understood. Nowadays cosmic ray exposure (CRE) dating methods allow dating the morphologic structures involved in sackung and can contribute at the understanding of their origin. In the Alps, the 5.3 km long Arcs sackung initiated during the activity of rock glaciers. Three samples from these faulted rock glaciers provide their first CRE ages and show that at 2000 m elevation these block accumulations moved during the Younger Dryas and stopped in early Holocene. Six 10Be ages of fault scarps show that the Arcs sackung lasted only a few thousand years and stopped at about 8462 ± 432 10Be yr. They also reveal that deformation migrated upslope in agreement with a mechanism of flexural toppling of vertical layers. This unique and long gravitational event, characterized by migration of the deformation, does not support earthquake shaking as triggering mechanism for individual faults. It shows that, in the upper Isère valley, slope deformation was delayed of several thousand years after glacial debuttressing, and is not anymore active despite its fresh morphology. 相似文献
A simple technique for studying near-bed hydrodynamics and sediment dynamics is presented. The method combines the use of (1) a benthic tripod hosting a series of electromagnetic current meters, and (2) a newly developed near-bed multi-level water-sediment mixture sampler. The instrument package was deployed successfully at a shallow water station in the eastern English Channel. The currents at elevation 0.9 m above the bottom were asymmetrical, the flood current peak being slightly stronger than the ebb current peak. At elevation 0.3 m above the bottom, the ebb/flood current peak asymmetry vanished. The observed SSCs (suspended sediment concentrations) were tidally modulated, with a contrasting vertical distribution over the ebb and flood phases of the tidal current: the profile was uniform in the ebb phase whereas a stratification appeared in the flood phase. The depth dependence and time evolution of the SSCs are attributable to a combination of local resuspension and advection-dispersion of remotely suspended fine sediment by ebb currents. Suspended sediment fluxes were uniform during the ebb phase and increased with elevation above the bottom during the flood phase. 相似文献
The development of the analytical theory of the motion of an artificial satellite (Berger, 1972–1975) points out the great importance of the second, third order and coupling terms between zonal harmonics. These
terms have been added to the equations established byKing-Hele andCook (1968–1973) for the determination of odd zonal harmonics. This solution is compared with theirs. It satisfies all the equations
much better and especially the equations relating to near-critical inclination satellites. 相似文献
A method for the determination of electron densities up to 1000 km by using data from vertical sounding and Faraday rotation techniques is suggested. Electron density profiles and contours plotted following this method are compared with results obtained by Evans using the incoherent scatter technique. 相似文献
Two highly active mud volcanoes located in 990–1,265 m water depths were mapped on the northern Egyptian continental slope
during the BIONIL expedition of R/V Meteor in October 2006. High-resolution swath bathymetry and backscatter imagery were
acquired with an autonomous underwater vehicle (AUV)-mounted multibeam echosounder, operating at a frequency of 200 kHz. Data
allowed for the construction of ~1 m pixel bathymetry and backscatter maps. The newly produced maps provide details of the
seabed morphology and texture, and insights into the formation of the two mud volcanoes. They also contain key indicators
on the distribution of seepage and its tectonic control. The acquisition of high-resolution seafloor bathymetry and acoustic
imagery maps with an AUV-mounted multibeam echosounder fills the gap in spatial scale between conventional multibeam data
collected from a surface vessel and in situ video observations made from a manned submersible or a remotely operating vehicle. 相似文献
As a result of the opening of the borders of the former Soviet Union, Israel has been the destination of numerous immigrants.
This article deals with the impact of immigration between 1989 and 1994, upon three towns in the south of Israel, Be'er Sheva,
Ashkelon and Kiriat Gat. These towns correspond to three socio-economic levels of urban area in the southern region. On the
one hand, the immigrants from the former Soviet Union arrive with specific demands, on the other hand the political, economical
and social context in Israel is very unusual. The sucessful integration of immigrants and the constructive development of
the host country depend on the conformity of these demands and proposals. What the government offers in terms of housing,
reception and employment in each of the three towns plays a key role: the town's social and economical heritage influences
the integration of the new population while at the same time the arrival of a new workforce influences the development of
the local area. Every town wants to grow and reinforce its position in the region, but only the large town, Be'er Sheva, is
able to offer a certain diversity and therefore answers more fully the needs and wants of this new population. Government
decisions and policies are not made to oppose the liberal economic system and to suppress the spacial inequalities despite
some measures aiming at a more equal balance. The importance of heritage and the lack of communal development schemes within
regions together ensure the continuation of qualitative inegalities in the south of Israel and even accentuate the problem.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献