Measurement of coherent elastic neutrino-nucleus scattering with ultra-radiopure NaI(Tl) crystals

为研究3英寸滨松R11065-20光电倍增管(PMT)输出的非线性，研制了一种低本底分压电路。用于分隔器的大多数放射性照相电子元件是使用神冈地下实验室的低本底高纯度锗探测器选择的。采用NaI(Tl)(碘化钠)晶体在神冈煤矿的低本底屏蔽下对研制的分压光电倍增管进行了测试。与滨松光电子公司提供的标准分压器的相同配置相比，测量结果显示出更低的本底水平。然而，对于高能，观察到了强烈的饱和。与滨松光电子公司讨论了这个问题。一种新的分压电路将与滨松的一名人员合作开发。一种新的5英寸超低本底NaI(Tl)探测器在神冈地下实验室进行了测试。用~(60)Co、~(133)Ba和~(137)Cs源对探测器进行了定标。在神冈地下实验室的低本底屏蔽下测量了5英寸NaI(Tl)晶体的放射性纯度。尽管210Pb的污染比预期的要高，但所开发的5英寸NaI(Tl)晶体是测量相干弹性中微子-核散射的优秀探测器。

A low-background voltage divider for 3-inch Hamamatsu R11065-20 photomultiplier (PMT) was developed to study non-linearity of the PMT output. Most radiopure electronic components for the divider were selected using a low-background high-purity germanium detector at the Kamioka underground laboratory. The PMT with the developed voltage divider was tested using　NaI(Tl) (sodium iodide) crystal in a low-background shielding at the Kamioka mine. The measurements demonstrated lower background levels in comparison to a same configuration with a standard voltage divider provided by Hamamatsu Photonics company. However, a strong saturation was observed for high energies. The problem was discussed with Hamamatsu Photonics company. A new voltage divider circuit will be developed in cooperation with a Hamamatsu personnel.A new 5-inch ultra-low-background NaI(Tl) detector was tested at the Kamioka underground laboratory. The detector calibration using 60Co, 133Ba and 137Cs sources was performed. The radiopurity of 5-inch NaI(Tl) crystal was measured in a low-background shielding at the Kamioka underground laboratory. Despite of a higher than expected contamination by 210Pb, the developed 5-inch NaI(Tl) crystal is an excellent detector to measure a coherent elastic neutrino-nucleus scattering.