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


Yucel H., Solmaz A. N. , Kose E., Bor D.

RADIATION PROTECTION DOSIMETRY, vol.138, no.3, pp.264-277, 2010 (SCI-Expanded) identifier identifier identifier

  • Publication Type: Article / Article
  • Volume: 138 Issue: 3
  • Publication Date: 2010
  • Doi Number: 10.1093/rpd/ncp239
  • Journal Name: RADIATION PROTECTION DOSIMETRY
  • Journal Indexes: Science Citation Index Expanded (SCI-EXPANDED), Scopus
  • Page Numbers: pp.264-277
  • Gazi University Affiliated: Yes

Abstract

When the high-resolution gamma-ray spectrometry was used in the analysis of U-234 and Th-230 in samples, there is a much more need to correct for the measured activity results of U-234 and Th-230 mainly due to self-absorption effects and the interfering lines from Ra-226, U-235, U-238 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 U-234 and Th-230 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 U-234 leads to a lager systematic error of 87.3-90.4 % for the measured activities of U-234, and similarly if one ignores the contributions of the interference gamma rays to the main analytical peak at 67.7 keV of Th-230, this leads to a much smaller systematic error of 2.1-2.7 % for the activities of Th-230. Therefore, the required correction factors for spectral interferences to the analytical peaks of U-234 and Th-230 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 U-234 and Th-230 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 U-234 and Th-230 while using gamma-ray spectrometry, thereby leading to inaccuracies in their derived quantities, for instance, the corresponding age determinations of the samples.