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

地下实验中的主要背景源，如寻找双β衰变，被认为是放射性物质，特别是环境中的Toron子核^<208>T1以及探测器本身。为了测量这种污染，通常使用具有氡灵敏度或检测极限为10 mBq/m^3量级的大容量静电收集型检测器。例如，在利用漂移室的实验配置的情况下，填充气体中的放射性污染的测量是至关重要的，本检测器似乎在估计气体中的氡以及Toron的微量方面是有用的。为了理解这种类型的检测器，我们研究了1升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和PIN光电二极管保持在负电位安装在顶部的内部容器， ...更多信息 R.将放射性离子如钋、铋等收集到二极管表面，探测到它们的α衰变，得到明显分离的几个峰。在测量中，探测器首先装在一个大的丙烯酸容器中，然后与外界空气隔离，观察到计数率随时间的变化。与上述大型检测器和准备好的源的情况相比，观察到的指定子核的半衰期不太准确。测量精度在3 ~ 4%水平.然而，本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变成正电子。这些离子也倾向于粘附水分子，结果由于寿命效应，离子可能在被检测到之前丢失。这种行为在过去由Chu和Hopke研究过，我们认为这是由于离子迁移率的降低。我们测量的α粒子产额的温度依赖性与预期的行为以及过去的result.Although目前的结果是只为水蒸气，大约相同的论点可能成立的酒精蒸汽，这是一种常见的淬灭气体在漂移室中是很好的协议。为了评价短寿命^ T1核的β衰变，需要对反应室气体中的钍系污染进行更仔细的研究<208>。另一个观察是稀有气体的环境。我们已经通过使用地幔来执行此操作。在氩气环境中的探测效率约为氦气的1/4。这一结果被认为是由电荷转移碰撞的离子与氩气原子。观察结果与这一假设非常吻合。少

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