AMS (Accelerator Mass Spectrometry) is the major method of the radiocarbon dating today. With the availability of other nuclides, such as ¹⁰Be, ¹²⁹I as well as ¹⁴C, AMS is applied widely to earth environmental sciences. The quality of AMS measurement, e.g., efficiency, sensitivity, is continuously developed whereas a new detection method for new nuclide is persuaded. This article surveys the technical points, application fields and history of AMS to help a comprehensive understanding and a future prospect of AMS.

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Accelerator mass spectrometry (AMS) is an analytical technique that combines an accelerator and a mass spectrometer. It has extremely high measurement sensitivity by removing isobar and isobaric molecular ions. In recent years, the study of new methods for separating isobars before the ions are injected into the accelerator, one of which is laser photo detachment (LPD), has been progressing. In LPD, only isobar ions are selectively neutralized and separated from the targeted ions by utilizing the difference in electron affinity. This paper aims to give an overview of LPD for AMS and introduce the LPD system being developed at MLAT as an example.

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trontium-90 (90Sr, 28.9 years) is a key fission product nuclide in internal dose assessment because it accumulates in bones and teeth in the body, causing health problems. Therefore, it is essential to know the distribution of 90Sr in the environment and its temporal variation (90Sr enrichment in biota), which requires efficient analysis of many environmental samples. The sensitive analysis of 90Sr with accelerator mass spectrometry (AMS) was developed in this study. In this study, the validity of the AMS method was demonstrated by analyzing environmental samples with known 90Sr concentrations (IAEA-447, IAEA-A-12, and IAEA-TEL-2015-03 sample 5: 1 dry-g each). The chemical separation developed in this study takes approximately two days and is a more straightforward procedure than conventional β-ray detection methods. The 90Sr measurements were conducted on the AMS system combined with the Ion Laser InterAction Mass Spectrometry (ILIAMS) system. The AMS method achieved a limit of detection <0.1 mBq (<1.3×105 atoms) for 90Sr, which is 1/30 of typical β-ray detection. As a result of the lower detection limit, the AMS method allows 90Sr quantification with smaller sample volumes. For example, a Japanese freshwater sample with a 90Sr concentration of 4 mBq/L requires a sample volume of 5 liters.

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Tono Geoscience Center, JAEA has started a project for developing a prototype downsized AMS system based on the surface stripper technique, the footprint of which is 1.9 m × 1.9 m. 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 and maximum ion energy is 40 keV.

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The recent development of the AMS-14C method requires more sophisticated pretreatment of dating samples. On the other hand, there is a need to promote a safe and efficient way for radiocarbon dating of various materials. During its chronological research, the National Museum of Japanese History (NMJH) introduced automatic ABA equipment to improve efficiency in the pretreatment of buried archaeological samples. For the tree rings, the bleaching of cross-sectional laths has dramatically improved the process of extracting cellulose.

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It is required to estimate absorbed dose in cellular regions considering fine ionization structure including effect of δ rays along α ray tracks including for improvement of α particle internal radiotherapy. The cloud concentration along α ray tracks observed in a cloud chamber corresponds to the ion density generated along α ray tracks. An adiabatic expansion cloud chamber was operated to capture α ray track images. Captured α ray track images were analyzed to obtain distribution of relative cloud density along the α ray track. Obtained distribution of relative cloud density along the α ray track exhibited similar profile of calculated distribution of absorbed dose along track of α ray passing through air by PHITS. Absorbed dose contributed by α and δ-rays in air and water were calculated by PHITS to confirm the feasibility of estimation of absorbed dose in cellular regions including fine structure of ionization phenomena along α ray tracks by utilizing analysis of α ray track images captured by the cloud chamber.

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