Aplicação de técnicas analíticas de espectrometria de massas para análises de amostras de esfregaço (swipe samples) para fins de salvaguardas nucleares

Abstract

The possibility of detecting undeclared nuclear materials and activities through environmental swipe samples analysis has become an important safeguards tool for the International Atomic Energy Agency (IAEA) since 1996. The goal of this study was to verify a methodology applicability for bulk analysis of this type of sample, basically consisted of the following steps: samples decomposition by incineration, acid digestion of the incineration residue, chemical separation of uranium by ion exchange chromatography and uranium total amount and isotopic composition measurements by mass spectrometry. Measurements of total uranium content were performed by inductively coupled plasma mass spectrometry (ICP-MS) and measurements of isotopic composition were performed by ICP-MS and by thermal ionization mass spectrometry (TIMS). Besides the validation of the adopted methodology through the evaluation of performance parameters, comparison of isotopic composition results between the two mass spectrometry techniques employed proved the methodology’s reliability. The average result of the uranium amount present in the process blank samples was (0.1113 ± 0.0205) ng; this result did not reveal a notable contamination in the workplace, although the methodology was not carried out in a laboratory with a clean room classification. The analysis of swipe blank samples allowed the verification of the amount and the isotopic composition of the uranium naturally present in the cotton filter material, in which the sample is collected; the amount of (2.747 ± 0.096) ng is within the range specified by the IAEA and the isotopic ratio n(U-235)/n(U-238) of (0.007841 ± 0.000142) is close to natural uranium. The appropriateness of the employed methodology was carried out through the analysis of simulated samples prepared with certified reference material and showed an accuracy of about 4% for uranium amount measurements and an accuracy of less than 1% for isotopic ratio n(U-235)/n(U-238) measurements. Finally, the analysis of real samples allowed the practical application of the methodology.