Methods for spectral interference corrections for direct measurements of 234U and 230Th in materials by gamma-ray spectrometry

Abstract

When the high-resolution gamma-ray spectrometry was used in the analysis of Th mainly due to self-absorption effects and the interfering lines from 226 Ra, 235U, 238 U and their decay products that often might be present in the samples. Therefore, in the present study, the methods for the spectral interference corrections for the analytical peaks of 234 U and 230 Th are suggested to take into account the contributions of the overlapping gamma rays to these peaks. For the method validation, direct gamma-ray spectrometric measurements were carried out using certified reference materials (CRM) by use of a 76.5 % n-type Ge detector. The activities measured for the CRM samples were corrected for spectral interferences, self-absorption and true coincidence-summing (TCS) effects. The obtained results indicate that ignoring of the contribution of the interference gamma rays to the main analytical peak at 53.2 keV of 234 U leads to a lager systematic error of 87.3-90.4 % for the measured activities of 234 U, and similarly if one ignores the contributions of the interference gamma rays to the main analytical peak at 67.7 keV of 230 Th, this leads to a much smaller systematic error of 2.1-2.7 % for the activities of 230 Th. Therefore, the required correction factors for spectral interferences to the analytical peaks of 234 U and 230 Th are not negligible and thus they should also be considered besides necessary self-absorption factors to determine more accurate activities in the samples. On the other hand, it is estimated that although the TCS effects on the main analytical peaks of both 234 U and 230 Th are negligibly small, those TCS correction factors for their interference gamma rays to these peaks should be taken into account when direct measurements are performed in a close-counting geometry condition. Otherwise, the resulted activities can have serious erroneous results for both 234 U and 230 Th while using gamma-ray spectrometry, thereby leading to inaccuracies in their derived quantities, for instance, the corresponding age determinations of the samples.

Determination of Uranium Isotopes in Environmental Samples Using Different Analytical Techniques: A Comparison

“…The activity concentration of 230 Th was determined using the emitted gamma-ray at 67.7 keV. After subtracting the 185.7 keV of 235 U, the 186.1 keV from 226 Ra's gamma-ray emission was used to calculate its accurate activity concentration [26,27]. 214 Pb's activity concentration was measured at 241.9, 295.2, and 351.9 keV, while 214 Bi and 210 Pb's activity concentrations were measured using 609.…”

A radiological index for evaluating the impact of an abandoned uranium mining area in Salamanca, Western Spain

“…El uso del pico de 1001 keV es posible ya que la concentración de actividad de las muestras utilizadas es elevada (García-Talavera, 2003). La concentración de actividad del 234 U se pudo determinar a partir del fotopico de 53.20 keV, sin embargo la interferencia debida al fotopico de 53.23 keV del 226 Ra lo impide en este tipo de muestras (Yücel et al, 2009). La concentración de actividad del grupo B fue determinada a partir de las emisiones gamma del fotopico de 67.7 keV del 230 Th (Lozano et al, 2001).…”

Attenuation Effect of Sample Container in Radioactivity Measurement by Gamma-ray Spectroscopy

“…Self-absorption and true coincidence summing corrections, which are the correction factors that need to be made in the radioactivity calculation, are also effective in the volume source geometry counted on the detector endcap. Self-absorption correction is a factor that is effective especially in high-density matrices containing elements with high atomic number, which occurs as a because of the absorption of gamma rays passing through the sample due to the sample matrix and density, causing losses in the photopeak count (Yücel et al, 2010). Therefore, this loss depends not only on the sample, but also on the sample container, as it depends on a process until it reaches the detector.…”