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Rezumat articol ediţie STUDIA UNIVERSITATIS BABEŞ-BOLYAI
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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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