Radiation Protection Dosimetry Advance Access published online on October 20, 2009
Radiation Protection Dosimetry, doi:10.1093/rpd/ncp239
METHODS FOR SPECTRAL INTERFERENCE CORRECTIONS FOR DIRECT MEASUREMENTS OF 234U AND 230Th IN MATERIALS BY GAMMA-RAY SPECTROMETRY
1 Turkish Atomic Energy Authority (TAEA), Besevler Yerleskesi, Tandogan, TR-06100, Ankara, Turkey
2 Present address: Institute of Nuclear Sciences of Ankara University (AU-INS), Tandogan, TR-06100, Ankara, Turkey
* Corresponding author: alfa.haluky{at}gmail.com; haluk.yucel{at}taek.gov.tr
Received June 30, 2009, amended September 16, 2009, accepted September 23, 2009
When the high-resolution gamma-ray spectrometry was used in the analysis of 234U and 230Th in samples, there is a much more need to correct for the measured activity results of 234U and 230Th mainly due to self-absorption effects and the interfering lines from 226Ra, 235U, 238U 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 234U and 230Th 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 234U leads to a lager systematic error of 87.3–90.4 % for the measured activities of 234U, and similarly if one ignores the contributions of the interference gamma rays to the main analytical peak at 67.7 keV of 230Th, this leads to a much smaller systematic error of 2.1–2.7 % for the activities of 230Th. Therefore, the required correction factors for spectral interferences to the analytical peaks of 234U and 230Th 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 234U and 230Th 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 234U and 230Th while using gamma-ray spectrometry, thereby leading to inaccuracies in their derived quantities, for instance, the corresponding age determinations of the samples.