Search

量子科学技術研究開発機構（QST）高崎量子応用研究所のイオン照射施設（TIARA）には4台の加速器が設置されており、主にバイオ技術や材料開発の研究分野へ様々なイオン種のビームを幅広いエネルギー範囲で提供している。AVFサイクロトロン（K110）、3MVタンデム加速器、3MVシングルエンド加速器、400kVイオン注入装置の2020年度運転時間は，それぞれ1879.8h，1629.0h，1637．8h，1555．1hであり，コロナ禍による施設の利用停止措置のため例年よりも短い運転となった。年間を通じて大きな故障はなく，コロナ禍による実験キャンセルを除けば，計画した照射実験はすべて実施した。主な保守・整備としては，サイクロトロンの共振器へ電力を供給するRFアンプの前段増幅部分について，800W真空管アンプから1ｋWトランジスタアンプへの変更を行った。これまで30年近く使用してきた真空管が製造中止になり，入手不能となっためである。主な技術開発として，タンデム加速器においてC60フラーレン専用イオン源の整備やフラーレン・マイクロビーム形成実験を実施した。本発表では，上記に加え，その他加速器の保守・整備及び技術開発，施設の利用状況について報告する。

Strontium-90 is one of the most important fission products due to the potential health risks of its uptake and retention in the human body. Conventional analysis techniques involve β counting, whic...

The Guangxi Zhuang Autonomous Region in southern China is one of the most typical karst relief areas with various forms, and tiankeng is one of the most typical karst relief forms of the Quaternary Period. In this work, accurate measurements of tiankeng exposure ages were made. The exposure ages of carbonate rocks from the five largest tiankengs in the world, the DaShiwei, HuangJing, ChuanDong, DaTuo, and DaCao tiankengs, were determined by accelerator mass spectrometry to be at least 20–400 thousand years, which provides significant proof for activity of new tectonic movement of the Eurasian continent in the Quaternary.

Tiankeng, a typical Karst relief of the Late Quaternary Period, in the south of China, plays an important role when researching the surface shape and evolution of the Karst relief. The accumulation of Chlorine-36 (T1/2 = 301 ka) through the interaction of cosmic ray particles with Ca, K and Cl in rocks allow it to be used as the ideal nuclide for determination of the exposure age and erosion rate of limestone. In this work, an improved 36Cl sample preparation method for Tiankeng limestone was presented. The Isotope Dilution-AMS technique allows for the simultaneous measurement of 36Cl and Cl with a single AMS sample preparation. The barium introduced during the sample preparation was removed to avoid ionizer poisoning and attain a higher and more stable beam current. The method is particularly suitable for limestone samples, as well as for soil, sediment and water samples.

The jungles of Linyun and Longlin Autonomous Prefecture, located in the heart of the southwestern Guangxi Zhuang Autonomous Region of China, are home to the oldest tea trees (Camellia sinensis) in the world. In the absence of regular annual rings, radiocarbon (14C) dating is one of the most powerful tools that can assist in the determination of the ages and growth rates of these plants. In this work, cores were extracted from large ancient tea trees in a central Longlin rain forest; extraction of carbon was performed with an automated sample preparation system. The 14C levels in the tree cores were measured using accelerator mass spectrometry (AMS) at the University of Tsukuba. These measurements indicated that contrary to conventional views, the ages of trees in these forests range up to ~700 years, and the growth rate of this species is notably slow, exhibiting a long-term radial growth rate of 0.039±0.006 cm/yr. It was demonstrated that 14C analyses provide accurate determination of ages and growth rates for subtropical wild tea trees.

The first preliminary test of the 14C-accelerator mass spectrometry (AMS) system at the University of Tsukuba was successfully performed using a gas/solid hybrid ion source and an automated sample preparation system with an elemental analyzer (EA). The maximum 12C− current of ∼11 µA was achieved using the optimized CO2 flow rate to the hybrid ion source. The machine background of 14C/12C for the AMS system reached to ∼2.4 × 10−16 (∼0.02 percent modern carbon, pMC) using unprocessed mineral graphite. Moreover, the blank level of 14C/12C including the combustion process for an IAEA-C1 graphite sample was 4.6 × 10−16 (0.05 pMC), demonstrating the low blank level of the automatic sample preparation system. In contrast, the blank level of 14C/12C including the combustion process for an IAEA-C1 CO2 sample was 5.0 × 10−15 (0.49 pMC), an order of magnitude worse than that for the graphite sample. The measurement uncertainty for the gas ion source was 0.6%, 2–3 times worse than that for the solid ion source (0.2%–0.3%).

To evaluate the environmental impact of 14C discharged to the atmosphere from the Tokai nuclear facility during normal operational periods, cores were extracted from an 80-yr-old pine tree that grew close to the Tokai Nuclear Power Plants (Tokai NPP and Tokai-2 NPP) and the Tokai Reprocessing Plant (Tokai RP), and the 14C levels in the annual rings were measured using accelerator mass spectrometry (AMS). The 14C activity ranged from 232 to 403 Bq kg−1 C in the tree rings formed during the period 1959–2013. The activities in the periods 1959–1965 and 2011–2013 represent the background levels, and the activities recorded between 1966 and 2010 are significantly elevated compared with these background levels, indicating uptake by the tree of 14C discharged from the Tokai nuclear facility. The excess 14C activity values of 1.1–70 Bq kg−1 C for the period 1966–2010 are positively correlated with the estimated total annual 14C discharges of 0.019–2.0 TBq from the Tokai NPP, Tokai-2 NPP, and Tokai RP (R2 = 0.72; n = 40). This activity of

A horizontal-type 6 MV Pelletron tandem accelerator was installed at the University of Tsukuba, Japan, in September 2014. The first test of the multi-nuclide accelerator mass spectrometry system was performed in March 2016, after two years of construction. This is the first report of its performance. The particle detection system was designed for high-sensitivity detection of 10Be, 14C, 26Al, 36Cl, 41Ca, and 129I. A five-electrode ΔE-E gas-ionization detector was installed as the end station of the detection system. The system background for 14C measurements, with the 4+ charge state at 5.0 MV, has a 14C/12C ratio of ∼2.4 × 10−16. 10Be, 26Al, 36Cl, 41Ca, and 129I have also been successfully detected. The 41Ca/Ca background is ∼3 × 10−15 as a result of improved isobaric separation techniques.

The anthropogenic long-lived radionuclide 129I is receiving increased attraction as a new oceanic tracer in addition to usage as a fingerprint of radionuclide contamination of the marine environment. To demonstrate the robustness of 129I as an oceanic tracer in the Northwest Pacific area, specifically in the Japan Sea, the input history of 129I to surface seawater was reconstructed using a hermatypic coral core sample from Iki Island in the Tsushima strait. Iodine isotopes in each annual band were measured using AMS and ICP-MS after appropriate pre-treatments of small amounts of coral powder. The 129I/127I ratios in the 1940s were almost at background levels (

A series of nuclides (14C, 26Al, and 36Cl) was measured using the 12UD Pelletron tandem accelerator before replacement by the horizontal 6 MV tandem accelerator at the University of Tsukuba Tandem Accelerator Complex (UTTAC). This paper considers the modification of the accelerator mass spectrometry (AMS) measurement parameters to suit the current 6 MV tandem accelerator setup (e.g., terminal voltage, detected ion charge state, gas pressure, and entrance window material in detector). The Particle and Heavy Ion Transport code System (PHITS) was also used to simulate AMS measurement to determine the best conditions to suppress isobaric interference. The spectra of 41Ca and 41K were then successfully separated and their nuclear spectra were identified; the system achieved a background level of 41Ca/40Ca ∼ 6 × 10 - 14 .

The anthropogenic long-lived radionuclide