Laser ablation inductively coupled plasma mass spectrometry for the trace, ultratrace and isotope analysis of long-lived radionuclides in solid samples

Abstract

The capability of laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) for determination of long-lived radionuclides in different materials (e.g., in geological samples, high-purity graphite and nonconducting concrete matrix) was investigated. The main problem in the quantification of the analytical results of long-lived radionuclides is that (except for geological samples) no suitable standard reference materials are available. Therefore, synthetic laboratory standards (graphite and concrete matrix doped with long-lived radionuclides, such as 99Tc, 232Th, 233U, 235U, 237Np, 238U) were prepared and used for quantification purposes in LA-ICP-MS. Different calibration procedures—the correction of analytical results with experimentally determined relative sensitivity coefficients (RSCs), the use of calibration curves and solution calibration by coupling LA-ICP-MS with an ultrasonic nebulizer—were applied for the determination of long-lived radionuclides, especially for Th and U in different solid samples. The limits of detection of long-lived radionuclides investigated in concrete matrix are determined in the pg g −1 range (e.g., for 237Np-50 pg g −1 in quadrupole LA-ICP-MS; for 233U-1.3 pg g −1 in double-focusing sector field LA-ICP-MS). Results of isotope ratio measurements of Th and U in synthetic laboratory standards and different solid radioactive waste materials of direct analysis on solid samples using LA-ICP-MS are comparable to measurements using the double-focusing sector field ICP-MS after separation of the analyte, even if no possible interference of atomic ions of analyte and molecular ions are expected. Furthermore, LA-ICP-MS allows precise and accurate isotope ratio measurements of Th and U in solid samples. For example, the isotope ratio 234U/ 238U = 0.000067 in radioactive reactor graphite was determined with a precision of 1.1% relative standard deviation (RSD).