Influence of neutorons and γ-rays in the underground laboratories for double beta decay experiment

(1) NEMO 3合作项目正在寻找中微子双β衰变，以研究亚ev区域的马约拉纳中微子质量。NEMO 3探测器的建造已经完成，探测器目前在Frejus地下实验室（Laboratoire de Souterrain de Modane， LSM）正常运行。在本研究中，我们研究了地下实验室中γ射线和中子的通量，这是双β衰变研究的背景。(2)采用大体积碘化钠（NaI）振荡器测量了LSM内的y射线通量。由于NaI对γ射线和中子都很敏感，我们采用了不同的屏蔽结构来提取纯γ射线通量。由于预期计数率很低，本实验已经进行了3年多。(3)氡是我们实验背景中最严重的来源之一。研制了高灵敏度的氡探测器，用于测量NEMO 3探测器所用的室内气体等的氡浓度。

(1) The NEMO 3 collaboration is looking for neutrinoless double beta decays to investigate Majorana neutrino mass in the sub-eV region. Construction of the NEMO 3 detector has been completed, and the detector is now operating normally in the Frejus underground laboratory (Laboratoire de Souterrain de Modane, LSM). In this research, we studied the fluxes of γ-rays and neutrons in the underground laboratory, which are the backgrounds of the double beta decay study.(2) We reported the y-ray flux measurement in the LSM using a large volume sodium iodide (NaI) scitillator. Since NaI is sensitive to both γ-rays and neutrons we used different shielding configurations to extract the pure γ-ray flux. Since the expected counting rate is very low, the present experiment has been carried out for more than 3 years.(3) Radon is known to be one of the most serious origins of background of our, experiment. High sensitive radon detectors are developed for the radon concentration measurement of the chamber gas etc. used for the NEMO 3 detector.