[1L07-09] Beam Diagnostics and Accelerator Technology

[1L08] Progress on Ultrasensitive Detection Techniques for Hard-to-measure Nuclide ⁴¹Ca with the 6 MV Tandem Accelerator Mass Spectrometry System

*Kimikazu Sasa¹, Seiji Hosoya², Tsutomu Takahashi¹, Kenta Takano¹, Yuta Ochiai¹, Yasuji Oura³, Keisuke Sueki¹ (1. Univ. Tsukuba, 2. QST, 3. Tokyo Metropolitan Univ.)

Keywords:Ca-41, Accelerator Mass Spectrometry (AMS), 6 MV tandem accelerator

⁴¹Ca (T_1/2= 1.04 × 10⁵ yr) is an ideal tracer on dating of the exposure age for meteorites and terrestrial surfaces. We have been developing ultrasensitive detection techniques for ⁴¹Ca-AMS with the 6 MV tandem accelerator. The ion source can extract CaF₃^- beams up to 500 nA from CaF₂ materials. In this study, we tried to detect a charge state of ⁴¹Ca⁵⁺ with a total energy of 32.5 MeV. The beam transmission of ⁴¹Ca⁵⁺ is about 7 %. A multi-plate gas-ionization detector is employed to separate ⁴¹Ca spectrum from isobaric interferences of ⁴¹K. We can obtain a background level of ⁴¹Ca/Ca ratio to about 3 × 10⁻¹⁵ and a measurement precision of 3% for 9.76 × 10^-12 isotopic ratio using the 6 MV AMS system.