Monday, 5 September 2005

This presentation is part of: Poster Session I

26Al and 36Cl AMS system at the University of Tsukuba: A progress report

Kimikazu Sasa1, Yasuo Nagashima1, Tsutomu Takahashi1, Riki Seki1, Yuki Tosaki1, Keisuke Sueki1, Kotaro Bessho2, Hiroshi Matsumura2, Taichi Miura2, and Ming He3. (1) AMS Group, University of Tsukuba, Tennoudai 1-1-1, Tsukuba, Japan, (2) Radiation Science Center, High Energy Accelerator Research Organization, Oho 1-1, Tsukuba, Japan, (3) Department of Nuclear Physics, China Institute of Atomic Energy, Beijing, China

　The present status of the Tsukuba AMS system on the 12UD Pelletron tandem accelerator is reported. At present, long lived radioisotopes of 26Al, 36Cl and 129 I are able to be measured by the Tsukuba AMS system. After the AMS-9 conference, several efforts have been paid on the 26Al and 36Cl-AMS system in order to improve the performance. Instead of the GVM stabilizer, a slit current feedback control system is used as a terminal voltage stabilizer. A molecular pilot beam method is applied to stabilize the terminal voltage. The terminal voltage is kept stably within 0.1% accuracy by this method. A tri-carbon molecular, 12C3− ion is used as the pilot beam for 36Cl-AMS. It is important to reduce the strong 36S isobaric interference on 36Cl measurements. Several improvements have been applied on the AMS beam line, so that 36Cl-AMS is able to be performed with 10 MV terminal voltage instead of 9 MV. Therefore, the energy of the 36Cl9+ beam increases from 90 MeV to 100 MeV. This energy increment helps us to get more clear separation between 36Cl and 36S. In addition, we developed a new gas ΔE−E counter telescope which consists of two gas ΔE sections and an ion implanted silicon surface barrier detector with the 45 × 45 mm2 active area. A 4 mm aramid film is used as the entrance window of the detector. As a result of these improvements, the detection efficiency of 36Cl increased to 1.5 times and the discrimination between 36Cl and 36S was much improved. Over all accuracy is ±3% and the effective detection limit is reached to 1 × 10−14 for 36Cl/35Cl ratio. In addition to the improvement of 36Cl-AMS, 26Al-AMS has also progressed in AMS technique. The ions extracted from the ion source were changed to 26AlO− ions from 26Al− because several advantages would be expected. 26MgO− molecular ion is used as the pilot beam. After passing through the accelerator at 10.2 MV, 26Al7+ and 26Mg7+ with the energy of 78 MeV are selected by the analyzing magnet. 26Al7+ ions are changed to full stripped 26Al13+ ions by a second charge exchange foil and then they are separated by the following energy and momentum selectors. The effective detection limit is reached to better than 5 × 10−15 for 26Al/27Al ratio.

See more of Poster Session I
See more of The 10th International Conference on Accelerator Mass Spectrometry (September 5-10, 2005)