Development of Ultra-high Sensitivity Analysis Methods for Very Small Amount of Radio-activitie Materials in Liquid-scintillator

液体闪烁体中极微量放射性物质超高灵敏度分析方法的发展

• 批准号: 13640254
• 负责人: SHIRAI Junpei
• 金额: $ 2.3万
• 依托单位: Tohoku university
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (C)
• 财政年份: 2001
• 资助国家: 日本
• 起止时间: 2001 至 2003
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-13640254/
• 关键词: Liquid Scintillator; KamLAND experiment; water extraction; Nitrogen purge; Reactor neutrino; ^7Be Solar neutrino; Neutron Activation Analysis; ICP-Mass Spectrometry; 純化装置; 液液抽出; 窒素ガスパージ; 放射性稀ガス; ニュートリノ; 原子反ニュートリノ; 放射化分析

The aim of the study is to develop analysis methods for very small amount of radio-impurities in the liquid scintillator which is used in a neutrino experiment KamLAND carried out by Tohoku University as a main institute in the underground laboratory in Kamioka mine in Japan. The study has also a scope of removing radio-impurities to realize real-time detection of low energy neutrinos below 1MeV region. ICP-Mass Spectrometry (ICP-MS) and Neutron Activation Analysis (NAA) methods were applied to the liquid scintillator purified by water extraction and nitrogen purge methods. As a result 10^<-13>g/g and 10^<-15>g/g sensitivities were achieved for ^<238>U/^<232>Th and ^<40>K, respectively. Removing contamination in the sample preparation was found critical to improve the analysis sensitivity. KamLAND reactor neutrino experiment was started as the required purity of the liquid scintillator was confirmed by the ICP-MS and NAA. The Bi-Po decay chains in the KamLAND data was found to be less than 1μBq/m^3 sufficient for doing ^7Be solar neutrino detection. These results showed that the purification methods are quite excellent and made good contribution for the discovery of the reactor anti-neutrino deficit by KamLAND. In sub-MeV region, a large amount of backgrounds from radio-activities mainly from ^<210>Pb and ^<85>Kr decays with long lives are found crucial for ^7Be solar neutrino experiment. The main purpose of this program was moved toward finding efficient removal methods of these elements and various efforts were made ; nitrogen purge by an upgraded test device for removing radioactive rare gases, and adsorption, filtration, adsorption as well as water extraction for removing ^<210>Pb. Precious data for further R&D studies have been accumulated.

该研究的目的是开发用于中微子实验KamLAND的液体闪烁体中的极少量放射性杂质的分析方法，该实验由东北大学作为日本神冈矿地下实验室的主要研究所进行。本研究还包括去除放射性杂质，实现1 MeV以下低能中微子的实时探测。采用电感耦合等离子体质谱（ICP-MS）和中子活化分析（NAA）方法对经水萃取和氮气吹扫方法纯化的液体闪烁体进行分析。结果，对μ U/μ Th和μ K的灵敏度分别达到10 μ <-13>g/g和10 μ <-15>g/g<238><232><40>。去除样品制备过程中的污染物是提高分析灵敏度的关键。由于ICP-MS和NAA确认了液体闪烁体的所需纯度，因此开始了KamLAND反应堆中微子实验。KamLAND数据中的Bi-Po衰变链小于1μBq/m^3，足以进行^7 Be太阳中微子探测。这些结果表明，这些提纯方法是相当优良的，为KamLAND发现反应堆反中微子亏损作出了很好的贡献。在亚MeV区，以^ Pb和^ Kr衰变为主的大量长寿命放射性活动背景<210><85>对^7Be太阳中微子实验至关重要。该计划的主要目的是寻找这些元素的有效去除方法，并进行了各种努力;通过升级的测试装置进行氮气吹扫以去除放射性稀有气体，以及吸附，过滤，吸附和水萃取以去除^<210>Pb。为进一步的研发研究积累了宝贵的数据。

项目成果

白井 淳平: "カムランド実験始まる"ニュークリアーフィジックスB(プロシーディングス サプリメント). 118. 15-22 (2003)

Junpei Shirai：“CamLAND 实验开始”《核物理 B》（论文集增刊）118. 15-22 (2003)。

J.Shirai, F.Suekane, K.Inoue: "KamLAND Experiment : To the Discovery of the Reactor Neutrino Deficit"High Energy News. Vol.22.1. 1-10 (2003)

J.Shirai、F.Suekane、K.Inoue：“卡姆兰德实验：发现反应堆中微子缺陷”高能新闻。