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MEASUEEMENT OF MINUTE AMOUNT OF RADON AND TORON CONTAMINATION IN THE CHAMBER GAS FOR USE IN THE DOUBLE BETA DECAY EXPERIMENT

双 β 衰变实验用室气体中氡气和 Toron 污染微量的测量

基本信息

批准号：
14540270
负责人：
KOBAYASHI Shigeharu
金额：
$ 2.18万
依托单位：
SAGA UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2002
资助国家：
日本
起止时间：
2002 至 2004
项目状态：
已结题

项目摘要

The major background source in the underground experiments, such as a search for the double beta decay, is recognized as the radio-active materials, specifically the daughter nucleus of toron, ^<208>T1, in the environment as well as the detector itself. To measure such contamination, a large volume electrostatic collection type detector having radon sensitivity, or the detection limit, of the order of 10 mBq/m^3 is commonly used. In case, for example, of an experimental configuration utilizing a drift chamber, the measurement of radio-active contamination in the filling gas is crucial the present detector seems to be useful in the estimate of minute amount of the radon as well as the toron in the gas. To understand such type of the detector, we have studied a general behavior of the 1 litter volume detector. Its construction was a SUS container capable to let the external air from the bottom and a PIN photodiode held at a negative potential was mounted at the top of the inside containe … More r. The radio-active ions, such as polonium and bismuth, are collected to the diode surface and their alpha decays are detected as dearly separated several peaks.In this measurement the detector was first housed in a large acrylic vessel, and next was isolated from the external air, and the change of counting rate with time was observed Since our measurements are for the natural radon and a weak toron source of the "mantle", the observed half lives to specify the daughter nuclei were less accurate compared with the case for large detector mentioned above and a prepared source. The precision of our measurement was at 3〜4 % level. However, the present detector would be much easier to handle to get various kinds of information related to its performance. The daughter nuclei such as ^<218>Po is likely to ionize positive by reacting with oxygen. These ions also tend to adhere the water molecules and as a result the ions may be lost before being detected due to the lifetime effect. Such behavior was studied in the past by Chu and Hopke, and we have considered this by the decrease in mobility of the ions. Our measurement of the temperature dependence of alpha particle yield was in good agreement with the expected behavior as well as the past result.Although the present result was only for the water vapor, about the same argument may hold for alcoholic vapor, which is a common quenching gas in the drift chamber. A more careful study will be needed for the thorium series contamination in the chamber gas to evaluate the beta decay of short lived ^<208>T1 nucleus. Another observation was for the environment of rare gases. We have performed this by using a mantle. The detection efficiency in argon gas environment was about 1/4 of the helium gas. This result was considered by a charge transfer collision of the ions with the argon gas atoms. The observation was in good agreement with this assumption. Less

地下实验的主要背景源，如寻找双β衰变，被认为是放射性物质，特别是toron的子核，^<208>T1，在环境和探测器本身。为了测量这种污染，通常使用具有10 mBq/m^3量级的氡灵敏度或检测限的大体积静电收集型检测器。例如，在利用漂移室的实验配置中，对填充气体中的放射性污染的测量是至关重要的，目前的探测器似乎在估计气体中氡和toron的微量方面是有用的。为了了解这种类型的检测器，我们研究了1凋落物体积检测器的一般行为。它的结构是一个SUS容器，能够让外部空气从底部进入，一个PIN光电二极管被安装在内部容器的顶部，保持在负电位…更多的放射性离子，如钋和铋，被收集到二极管表面，它们的α衰变被检测到有几个分离的峰值。在此测量中，探测器首先被安置在一个大的丙烯酸容器中，然后与外部空气隔离，并观察计数率随时间的变化。由于我们的测量是针对天然氡和“地幔”的弱toron源，与上述大型探测器和制备源的情况相比，观察到的半衰期来指定子核的准确性较低。我们的测量精度在3 ~ 4%的水平。然而，目前的检测器将更容易处理，以获得与其性能相关的各种信息。子核如^<218>Po可能通过与氧反应而电离为正电。这些离子也倾向于附着在水分子上，因此，由于寿命效应，离子可能在被检测到之前就丢失了。这种行为在过去由Chu和Hopke研究过，我们通过离子迁移率的降低来考虑这一点。我们测量的α粒子产率与温度的关系与预期的行为以及过去的结果很好地吻合。虽然目前的结果只适用于水蒸气，但同样的结论也适用于酒精蒸汽，它是漂移室中常见的淬火气体。需要对室内气体中的钍系列污染进行更仔细的研究，以评估短寿命的^<208>T1核的β衰变。另一个观测对象是稀有气体的环境。我们是用斗篷来完成的。氩气环境下的检测效率约为氦气的1/4。这一结果是通过离子与氩气原子的电荷转移碰撞来考虑的。观察结果与这一假设非常吻合。少

项目成果

期刊论文数量（19）

专著数量（0）

科研奖励数量（0）

会议论文数量（0）

专利数量（0）

NEMO collaboration, Possible background reduction in double beta decay Experiments

NEMO 合作，双贝塔衰变实验中可能的背景减少

DOI：
发表时间：
2003
期刊：
Nuclear Instruments and Methods in Physics Research A503
影响因子：
0
作者：
H.Ohsumi et al.;NEMO collaboration;R.Arnold et al.
通讯作者：
R.Arnold et al.

L.Saha: "Study of DOI Resolution and Imaging Resolution of a PET Device"Nuclear Instrument and Methods in Physical Research. A in press. (2004)

L.Saha：“PET 装置的 DOI 分辨率和成像分辨率的研究”物理研究中的核仪器和方法。

DOI：
发表时间：
期刊：
影响因子：
0
作者：
通讯作者：

NEMO collaboration, Intitial Runs of NEMO 3 Experiment

NEMO 合作，NEMO 3 实验的首次运行

DOI：
发表时间：
2003
期刊：
Nuclear Physics(Presented by H.Ohsumi) A721
影响因子：
0
作者：
H.Ohsumi et al.;NEMO collaboration;R.Arnold et al.;H.Ohsumi et al.
通讯作者：
H.Ohsumi et al.

Possible background reduction in Double beta decay experiment

双β衰变实验中可能的背景减少

DOI：
发表时间：
2003
期刊：
Nuclear Instruments and Methods in Physics Research A 503
影响因子：
0
作者：
H.Ohsumi et al.;NEMO collaboration;R.Arnold et al.;H.Ohsumi et al.;H.Ohsumi et al.
通讯作者：
H.Ohsumi et al.

Initial Runs of the NEMO III Experiment

NEMO III 实验的初始运行