Status report of the Tsukuba 6 MV multi-nuclide AMS system: Progress in iodine-129 AMS
Ms Masumi Matsumura1, Dr Kimikazu Sasa1, Dr Aya Sakaguchi1, Dr Tetsuya Matsunaka2, Mr Tsutomu Takahashi1, Prof Keisuke Sueki1
1University Of Tsukuba, Tsukuba, Japan, 2Kanazawa University, Kanazawa, Japan
The 6 MV Pelletron tandem accelerator (model 18SDH-2 Pelletron, NEC, USA) has been utilized for various researches at the University of Tsukuba, Tandem Accelerator Complex (UTTAC) since 2016 (K. Sasa et al., 2015). The rare-particle detection system on the 6 MV Pelletron tandem accelerator (Tsukuba 6 MV multi-nuclide AMS system) was developed for high-sensitivity detections of ¹⁰Be, ¹⁴C, ²⁶Al, ³⁶Cl, ⁴¹Ca, and ¹²⁹I (K. Sasa et al., 2018), and also expected to measure other radioisotopes such as ⁹⁰Sr (K. Sasa, et al., 2021). The background of the system for isotopic ratio of ¹⁰Be, ¹⁴C, ²⁶Al, ³⁶Cl, ⁴¹Ca, and ¹²⁹I show ≤ 2×10-¹⁵, ≤ 2×10-¹⁶ (Graphite), ≤ 1×10-¹⁶, ≤ 3×10-¹⁵, ≤ 3×10-¹⁵, ≤ 2×10-¹⁴, respectively. The total experimental beam time and AMS measuring time of the 6 MV Pelletron tandem accelerator are approximately 6,130 hours and 3,800 hours, respectively, since 2016. The total number of AMS measuring samples is approximately 3,570. The Tsukuba 6 MV multi-nuclide AMS system has been applied to environmental researches, for example, ¹⁰Be in rainwater samples, ³⁶Cl in rainwater, ice core and soil samples, and ¹²⁹I in rainwater, riverwater, soil, seawater and coral samples (A. Sakaguchi et al., 2018). In 2020, we have measured the certified materials of ¹²⁹I, the Standard Reference Material® 3230, Level Ⅰ and Level Ⅱ, provided from the National Institute of Standards and Technology (NIST, USA). They were normalized by using Purdue-2 STD (Z94-0596) with an ¹²⁹I/¹²⁷I ratio of 6.5400 × 10−¹¹ (P. Sharma et al., 1997) (the value was revised in 2014 (M. Caffee, Purdue University, Private communication)), which was provided by the Purdue Rare Isotope Measurement Laboratory (PRIME Lab) at Purdue University, USA. The nominal ¹²⁹I/¹²⁷I ratios are (4.920 ± 0.062) × 10−¹⁰ and (0.985 ± 0.012) × 10−¹², for NIST 3230- Level Ⅰ and Level Ⅱ, respectively. The two samples after sputter-cleaning for 1 or 5 min. were measured in each run. The measured values of Level Ⅰ are approximately 10% lower than the nominal one. The resulting ratio and standard deviation (1σ) of the precision are (4.361 ± 0.058) × 10−¹⁰ (1.3%) and (0.909 ± 0.065) × 10−¹² (7.1%), respectively. We will report current status, memory effect and performance of ¹²⁹I measurement for the Tsukuba 6 MV multi-nuclide AMS system. In addition, we will introduce a development plan for the iodine-129 standard reference materials at UTTAC in this presentation.
Author is engaged in AMS research field at the University of Tsukuba since 2007.