Speaker
Description
Long-lived nuclides $^{10}$Be, $^{14}$C, $^{26}$Al, $^{36}$Cl, $^{41}$Ca, $^{90}$Sr, and $^{129}$I have been successfully detected with the 6 MV accelerator mass spectrometer at the University of Tsukuba [1]. $^{36}$Cl is one of the most difficult radionuclides to measure due to contamination with the interfering isobaric $^{36}$S. Sulfur itself is easily present in the environment, making its removal difficult. In order to separate and discriminate $^{36}$S, we have studied acceleration conditions, methods to reduce $^{36}$S in the beam itself emitted from the Cs sputtering ion source, and to separate and identify the spectrum between $^{36}$Cl and $^{36}$S incident on the detector [2]. To reduce $^{36}$S, we compared the material of the cathode in which the sample is loaded, a copper cathode filled with AgBr powder and a cathode with Ta metal attached. The sample cathode made of Cu, filled with AgBr, and with a 1 mm diameter hole had the lowest contamination of $^{36}$S. When the sample volume is large, AgCl is placed on the entire surface. In addition, we attempted to suppress $^{36}$S contamination by covering the surface of the wheel disk with a 0.5 mm Ta plate. As a result, the contribution of $^{36}$S was reduced by a factor of 50. $^{36}$Cl detection performances of Cl$^{5+}$ (30.0 MeV), Cl$^{7+}$ (48.0 MeV), and Cl$^{8+}$ (54.0 MeV) were compared by acceleration at 6 MV. We also compared how the spectrum separation changes with the gas pressure in the gas ionization chamber. As a result, background values were ~3 × 10$^{-15}$ for all charge numbers q=5+, 7+, and 8+. Cl$^{7+}$ (48.0 MeV) is commonly used for $^{36}$Cl AMS at the University of Tsukuba because the beam transmittance is as high as about 14% and the effect of interfering nuclides on the spectrum is small. In this presentation, we will report on progress in $^{36}$Cl AMS detection techniques and applied researches with the 6 MV tandem accelerator.
References
[1] K. Sasa et al., Nucl. Instrum. Methods Phys. Res. B, 437 (2018) 98.
[2] S. Hosoya, K. Sasa et al., Nucl. Instrum. Methods Phys. Res. B, 438 (2018) 131.
| Student Submission | No |
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