Project for Development of a Downsized AMS System based on the Surface Stripper Technique

Dr Natsuko Fujita1, Dr Akihiro Matsubara1, Dr Kenji Kimura1, Dr Yoko Saito-Kokubu1

1Japan Atomic Energy Agency, Gifu, Japan

Over the last decade, significant technological advances were made to downsize the AMS systems. The state of the art technology has reached a stage in development of ¹⁴C-AMS systems with a footprint below 2 m × 2 m [1]. The toughest hurdle for further downsizing is to overcome low transmission and high background caused by collisional processes with a stripper gas used to destroy interference isobaric molecules such as ¹²CH₂, ¹³CH.
A novel stripper technique based on specular reflection of fast ions on a single crystal surface, so called “surface stripper”, was proposed as a gas free stripper [2]. During the reflection, the ions interact with surface electrons and atoms. This may result in dissociation of those isobaric molecules. A numerical study to evaluate the survival probability of the isobaric molecule in the surface stripper has suggested the sufficient isobar suppression capability of the surface stripper for the practical use [3].
Japan Atomic Energy Agency has started a project for developing a prototype downsized AMS system (with the footprint of the system is 1.9 m × 1.9 m) based on the surface stripper technique. Although the system configuration using an ion source, magnets, and detectors is similar to that in conventional systems, there is no tandem accelerator as well as a gas stripper. The ion acceleration is provided in the ion source (maximum ion energy 40 keV). As the element of the surface stripper, a single crystal is placed between injection and analyzing magnets. The most remarkable feature of the system is that the post stripper beam line can be rotated horizontally as a unit (from the analyzing magnet to the rare detection) around the reflection point on the crystal surface so that the reflected ions can be analyzed. For proof-of-principle experiments, we have planned two steps: (1) Observation of the specular reflection and the dissociation by using a compact electrostatic analyzer located just behind the stripper, and (2) Demonstration of ¹⁴C measurement, along with the experimental confirmation of the isobar suppression capability of the surface stripper.

[1] H.-A. Synal, et al., Nucl. Inst. and Meth. B 294 (2013) 349.
[2] A. Matsubara, et al., Nucl. Instr. Meth. Phys. Res. B 437 (2018) 81-86.
[3] A. Matsubara, et al., submitted to the AMS-15 conference.


JAEA has a project for development of a downsized AMS system based on the surface stripper technique.

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