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    STUDIA GEOLOGIA - Ediţia nr.1 din 2007  
         
  Articol:   ESTIMATION OF ENVIRONMENTAL RADIONUCLIDE CONCENTRATION IN SOILS, A COMPARISON OF METHODS FOR THE ANNUAL RADIATION DOSE DETERMINATION IN LUMINESCENCE DATING.

Autori:  ALIDA TIMAR, CONSTANTIN COSMA, ROBERT BEGY, GABOR SZEILER, DUMITRU BARBOS, DAN FULEA, BENEA VASILE.
 
       
         
  Rezumat:  A study was made to compare and test the performance of several methods for the annual radiation dose determination in luminescence dating. The following techniques were compared: instrumental neutron activation, high-resolution gamma spectrometry, and alpha spectrometry. In the case of instrumental neutron activation, 238U, 232Th, and 40K concentrations were determined using the Zirconium standardization method. Detailed analysis was carried out using high-resolution gamma spectrometry, the activities of different nuclides (234Th, 226Ra, 214Pb, 214Bi, 210Pb, 228Ac, 208Tl) in the uranium and thorium chains being measured, as well as 40K. The advantage of this method is that radioactive equilibrium or disequilibrium in the uranium series can be checked. In the present work, the direct measurement of 226Ra, which can give extra information on the interpretation of the radioactive equilibrium, was implied. Since there is a serious spectral interference (up to 43%) on its 186.2 keV gamma line (by 235U at 185.7 keV) the correction procedure was outlined. Radon loss due to sample preparation was also investigated and an average loss of 15% was observed. Thus we stress upon the need for storing the samples for three weeks before measurement in order for the radioactive equilibrium to be reached again. A constant underestimation of 214Bi activities compared to 214Pb was observed. Since 214Bi and 214Pb should be in equilibrium, this can be attributed to summing-out effects. We recommend that in the case that no corrections are made to derive the activity of radon daughters from the activity of 214Pb instead of computing average value including also 214Bi. Moreover, concentrations of 210Po, 226 Ra, and 238 U were determined through alpha spectrometry measurements.  
         
     
         
         
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