Study of 48Ca Double Beta Decay

双β衰变的观测证明了轻子数守恒的违反。这是回答为什么我们的宇宙是由物质主导的关键实验。本研究项目旨在研究48Ca的双β衰变，其中以CaF2晶体为特征的candle探测器系统正在建设中。今年是这项研究的最后一年。幸运的是，我们继续研究的请求得到批准，我们的最后一年成为基础研究S的开始年，这大约是我们预算的两倍。今年我们取得了以下成绩：我们建造了容器和油品净化系统。我们现在几乎有了探测器的所有元件。将新设计的PMT浸入水中并进行了耐久性试验。我们发现了一些问题并解决了它。我们研究了给定PMT数量下PMT的最佳排列。购买了更多的CaF2晶体。我们研究了放射性背景水平，发现它们都是ok的。对这个实验来说非常重要的几乎唯一的背景是可能在Q值区域给出背景的-和-粒子的连续衰变。对脉冲形状的观察将为我们研究500mhz闪存ADC.6的特性提供判别背景的信息。虽然我们在大阪大学附近的Oto宇宙天文台工作，但蜡烛探测器系统太大了，Oto很难容纳探测器。我们与ICRR进行了讨论，我们决定在神冈地下实验室安装candle III。我们于2005年9月16-20日在夏威夷毛伊岛组织了“双β衰变和中微子质量”的美日研讨会。在这次研讨会上，我们讨论了双β衰变的研究现状。这有助于我们的实验得到认可。我们目前正在研究我们在大阪大学建造的探测器的特性。研究结束后，我们将探测器系统移至地下实验室，开始数据采集。少

The observation of double beta decay demonstrates the violation of Lepton Number conservation. It is a key experiment to answer the question why our universe is matter dominated. This research project aims at studying the double beta decay of 48Ca for which the CANDLES detector system, which features CaF2 crystals, is under construction. This year is the final year of the research. It is fortunate that our request to continue the research approved and our final year becomes the starting year of the basic Research S which roughly doubles our budget.We have achieved the following this year.1. We constructed vessel and oil purification system. We now have almost all elements of the detector.2. Newly designed PMT's are immersed in pire water and endurance test was performed. We found some problem and fixed it.3. We studied best arrangement of PMT for given number of PMT's.4. Additional CaF2 crystals were purchased. We studied radioactive background level and found that all of them are OK.5 … More . The almost unique background which is serious to this experiment is the successive decay of beta and alpha particles that may give background at the Q value region. The observation of pulse shape will give us information to discriminate the background for which we studied characteristics of 500 MHz flash ADC.6. Although we are working at Oto cosmo observatory near Osaka University, the CANDLES detector system becomes so large that Oto will have difficulty to accommodate the detector. We had discussion with ICRR and we decided to install the CANDLES III at Kamioka underground laboratory.7. We organized US-Japan seminar on "Double beta decay and neutrino masses" at Maui Hawaii from September 16-20, 2005. In this seminar we discussed current status of study of double beta decay. It helped to have recognition of our experiment.We are currently studying characteristic of the detector we constructed at Osaka University. After that study we will move the detector system to underground laboratory and start data taking. Less