Measurements of 41Ca in biological samples by Accelerator Mass Spectrometry using CaF2 target

For determining numbers of Ca-41 labeled biological samples, the analytical method of Ca-41/Ca-40 by Accelerator Mass Spectrometry (AMS) using GaF2 target was developed at the Beijing HI-13 AMS System. Ca-41 in the biological samples and Ca-41 standard samples were prepared to GaF2 with a more effective chemical separation and purification procedure. In the Ca-41 AMS measurement, CaF3- negative ion was extracted from ion resource, 7(+) charge state of particles was chosen after carbon foil stripping and accelerated at 8.5MV terminal voltage. Ca-41 ions were finally recorded by an 140mbar P10 gas filled multi-anode ionization chamber detector. The results showed that Ca-41 and the main isobar, K-41 could be clearly identified in the two-dimensional density spectra, and the interference of K-41 to Ca-41 was eliminated with the very low K-41 counting rate. The absolute measured values of 4 standard samples with Ca-41/Ca-40 in the range of 1.785 x 10(-8)-1.750 x 10(-10) were in good linear relationship with the standard values (r(2) = 0.997). After normalized with the 1.785 x 10(-8) Ca-41/Ca-41 standard, the measured values of S2 and S4 standard samples were in good agreement with the nominal values, however, the measured value of S3 deviated the nominal value largely. The Ca-41/Ca-40 of the biological blanks were estimated below 8.2 x 10(-13).