The Cris/Koeroes Rivers content of U, Th and K in the bottom sediment

A quantitative evaluation of uranium, thorium and potassium was made by processing of complex gamma spectra of natural radioactive series U (U-238), Ac U (U-235) and Th (Th- 232) and natural radioisotope K-40. Characteristic photogaff: uranium E?=1.764 MeV, thorium E?=2.620 MeV and potassium E?=1.462 MeV. We have used a detector Ge-Li of a high resolution (ca. 3.8 KeV ) and on electronic chain: Canberra (USA), preamplifier model 970, spectrometric amplifier Tennelec TC-2 49 (Oxford). For identifying of photogaff we have used covell method (n=5). Time 80,000 seconds. The Cris/Koeroes drainage covers about 275,300 Km2 (the most important rivers are Barcau/Berefhya, Crisul Repede/Sebes Koeroes, Crisul Negru, Crisul Alb, Cris/Kettoes Koeroes , and Cris/Harmas Koeroes). The solid discharge of these rivers varies from 0.33 Kg/s to 11.20Kg/s. The transported matter is composed by different size of gravel in coarse sand or coarse silts matrix. The median of gravels varies between -4.50 F and -0.60 F (23.63-1.52 mm), while the median of the gravels matrix varies between -1.80 F and 7.40 F (3.45-0.051 mm). Downstream detrital matter become more fine, especially along the banks. Alogene elements modify enough the sediment composition. As concerns mineralogy, the matrix of alluvia consists in quartz (31-74%), evenly distributed, feldspars (8-18%) and clay minerals (9-35%), more and more abundant towards the confluence with the Tisza River. The evaluation of contents of U, Th and K of bottom sediments was made on the basins of samples obtained in 8-16 August 1994, 21-30 July 1995 and from the transported matter of Crisul Negru and Crisul Baita in 4-9 September 2003. The share of uranium (0.78 - 9.14 ppm) and thorium (5.06 - 51.38 ppm) from the bottom sediments increases downstream, where heavy metals are trapped in the composition of clay minerals. In the sediments of the Crisul Alb, the distribution of potassium (K) resembles the one in Crisul Negru and is relatively constant, notwithstanding the grain-size spectrum; it is worth mentioning that in the sediments of the Crisul Negru the amount of K increases towards downstream, in relation with the clay fraction. The amount of uranium (U) in the sediments is twice lower than in those of the Crisul Negru. In the sediments of the Crisul Alb, thorium (Th) has a concentration 2/3 lower than in those of the Crisul Negru. In the Barcau, both elements increase from upstream (coarse sand) towards downstream (fine silt), as sediments become more and more fine. In the bottom sediments of the Crisul Repede, uranium and thorium are low and relatively constant; the maximal values were found at the confluence with the Iad