The status report on MALT-AMS system and application studies

Prof. Hiroyuki Matsuzaki1, Mr. Hironori Tokuyama1, Ms. Yoko S. Tsuchiya1, Mr. Takeyasu Yamagata1, Ms. Miwako Toya1, Dr. Yasuto Miyake2

1MALT, The University Of Tokyo, Tokyo, Japan, 2RIKEN, Wako, Japan

MALT (Micro Analysis Laboratory, Tandem accelerator, The University of Tokyo) is an ion beam analysis facility consist of a negative ion source, injection analysis system, a 5MV tandem accelerator, a high energy analysis system, and 5 beam courses. Among various beam analysis techniques, AMS (Accelerator Mass Spectrometry) is regarded as most important. Since the beginning of the operation of MALT (1993), AMS of various nuclides had been developed and used for application studies.
The accelerator is a Pelletron 5UD type tandem accelerator provided by National Electrostatics Corporation (nec) which generated 5 MV at the maximum. The ion source is 40-cathodes MC-SNICS. The sequential injection system and multi-Faraday cups system make possible the measurement of isotopic ratio. The detector for the rare isotopes is original made GIC (Gas Ionization Chamber). This GIC serves for the detection of Be-10, Al-26, Cl-36, Ca-41, I-129, and U-236. For Cl-36, GIC is set after a gas filled magnet. C-14 is measured by a semi-conductor detector.
Recently we have developed a new method for Ca-41 AMS. Just using presenting apparatuses, the background level of 2.0E-13 was achieved. We used CaF2 as the target material and 5.0 MV as the terminal voltage and 5+ charge state. Due to low current (< 300 nA) of CaF3- from CaF2 and not so high charge fraction (3%), the detection efficiency is not so high. At the final detector various unknown species are observed other than Ca-41. We are now trying to improve the background by an optimization of the configuration of GIC with the aid of simulation of ion and ionized electrons behavior.
At the first attempt, we detected U-236 (reported on AMS-14) using simply our GIC. The main factor limiting the background is U-235. By the calculation of the effect of our analyzing apparatus, i.e., the analyzing magnet, the switching magnet, and the electrostatic analyzer, the velocity of U-235 interfering at the final detector is found to be different from U-236. From this consideration, we are now introducing TOF system.
Stimulated by VERA’s achievement we began to test the LPD (Laser Photo Detachment). We made a test-bench beam line involving the key device for LPD, an ion cooler with RFQ. Though our test-bench beam line is an assembly from junk parts, we successfully observe the negative ion reduction in the case of Sulfur beam by the 532 nm laser. However there are many challenges before the implementation to the real beam line.
MALT is a common use facility for academic scholars and various scientific studies are conducted using AMS, especially earth-environmental studies using both the natural occurred nuclides and anthropogenic nuclides.


Head of MALT (Micro Analysis Laboratory, Tandem accelerator), The University of Tokyo. The speciality is AMS and Isotope Geochemistry. He had developed methods of AMS for various nuclides. In the application field, he stresses on the Iodine isotope system. He is also a faculty member of Department of Nuclear Engineering and Management, School of Engineering and studies and teaches mainly nuclides analysis and environmental impact assessment of artificial nuclides.

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Nov 08 - 19 2021