As it is well know, uranium is now recognized as a ubiquitous element, easily recognizable also in small occurrence. Their concentration in carbonate rocks is of the same order of magnitude as the lithospheric content (2.2 ppm). Uranium can replace calcium in the lattice of calcite or be adsorbed by the principal phosphate minerals. The large uranyl ions are adsorbed easily and can form the soluble complex UO2 (CO3)24+. The Uranium ionic radium (1.05 A°) is almost similar to one of Calcium (1.06 A°). Uranium is assumed to move freely in the water of soil profile after the processes of dissolution and precipitation of carbonate parent material occurred. It is claimed that its mobility is favoured by acid conditions, whereas in an alkaline pH the adsorption of its oxide would be increased. Until now very few papers studied natural Uranium in soils. Recently, the concentration of naturally occurring radionuclides (238U, 232Th, Knat) was measured in some Red Mediterranean soils from carbonate rocks in Spain, Italy and Turkey using gammaray spectrometry at the Gran Sasso National Laboratory of INFN (Italy). The Uranium content ranges from 1 to 5 ppm, the content for Thorium ranges from 3 ppm up to 30 ppm, whereas for Potassium varies between 0.13% and 1.3%. The results indicated that soils characterised by absence or scarcity of 2:1 clay minerals are poor in uranium, whereas soils with illite–smectite as the dominant minerals in clay fraction are noticeably richer.
Continuing some previous study on the paleosols natural radioactivity, this research demonstrated that soil Fe/Mn glaebules (nodules and concretions as well as the related coatings) are able to capture and include significant uranium contents together with some rare heavy metals. The research was carried out using thin section autoradiography by CR 39 transparent plates in order to locate the alpha track emitters. Transparent plates of CR 39 (artificial poly carbonate) were placed for exposition on the glaebules polished section for several months. After a chemical etching (by a NaOH solution) of CR 39 detectors to show alpha tracks damage, their location on thin section by overlapping of CR 39 transparent plates and the corresponding density of tracks (proportional to % of U ( being assumed the thorium absence) was performed by an image analysis software (Image J). Some results were validated by the gamma- ray spectrometry and also suggested useful application to identify the uranium movement along soil profile and as strong relationship which are like to exist between uranium and some component of organic matter as well as the phosphate material and natural bitumen in both soils and some carbonate rocks.