Measurements of 41Ca in Biological Samples by AMS Using CaF2 Target

Abstract: For determining numbers of ⁴¹Ca labeled biological samples, the analytical method of ⁴¹Ca/⁴⁰Ca by Accelerator Mass Spectrometry (AMS) using CaF₂ target was developed at the Beijing HI-13 AMS system. ⁴¹Ca in the biological samples and ⁴¹Ca standard samples were prepared to CaF₂ with a more effective chemical separation and purification procedure. In the ⁴¹Ca 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. ⁴¹Ca ions were finally recorded by an 140mbar P10 gas filled multi-anode ionization chamber detector. The results showed that ⁴¹Ca and the main isobar, ⁴¹K could be clearly identified in the two-dimensional density spectra, and the interference of ⁴¹K to ⁴¹Ca was eliminated with the very low ⁴¹K counting rate. The absolute measured values of 4 standard samples with ⁴¹Ca/⁴⁰Ca in the range of 1.785×10^－8—1.750×10^－10 were in good linear relationship with the standard values (r²=0.997). After normalized with the 1.785×10^－841Ca/⁴⁰Ca 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 ⁴¹Ca/⁴⁰Ca of the biological blanks were estimated below 8.2×10^－13.