Development of a front detector for reactor neutrino oscillation experiments

我们开发了一种新的反中微子探测器技术，用于读卡器中微子振荡实验“KarnLAND”的前探测器。在包括卡姆兰在内的有液体闪烁体的情况下，延迟符合技术对降低背景有很强的效果。但是，需要在反应堆附近测量读取器反中微子谱以了解无振荡中微子谱的前探测器应该工作在地面附近，而不是地下深处，那么即使延迟巧合也不能拒绝由地面大通量宇宙射线伪造的所有背景事件。然后我们开始开发一种具有粒子识别和方向测量能力的新型探测器。我们制造了以下两个探测器原型。第一个是分段检测器。使用该探测器，我们证实了顶点的位置分辨率提高到几厘米。在这种高分辨率下，利用真实事件和虚假事件顶点拓扑结构的差异，可以将假延迟巧合事件的宇宙生成快中子事件与真实的反中微子事件区分开来。我们计划把这个原型探测器放在任何反应堆的前面。第二个原型探测器是一个“成像相机探测器”，它采用CCD相机和图像增强器来拍摄每个事件的闪烁点的照片。利用该技术，我们的目标是以~1cm或更好的分辨率检测提示点和延迟点，以测量这些点的相对位置，从而测量反中微子的入射方向。使用原型探测器，我们成功地拍摄了宇宙射线μ子轨迹的照片。我们计划改进这个探测器来探测中子事件，也探测具有方向灵敏度的反中微子事件。

We have developed techniques of new anti-neutrino detectors for a front detector of a reador neutrino oscillation expertnent “KarnLAND". In everinents with liquid scintillator, including KamLAND, the delayed coincidence technique works strongly to reduce background. However, the front detector, which should measure the reador anti-neutrino spectrum near the reactors to know the neutrino spectrum without oscillation, should work near the ground level, not deep underground, then even delayed coincidence cannot reject all background events faked by large flux of cosmic rays at ground level. Then we started development of a new detector with an ability of particle identification and directional measurement. We produced the following two prototype detectors. The frst one is a segmented detector. Using this detector we confimned that the position resolution of vertexes is improved to several centimeters. With this high resolution, cosmogenic fast neutron events, which fake delayed coincidence events, can be distinguished from real antineutrino events using the difference of topology of vertexes between real and fake events. We plan to place this prototype detector in front of any of reactors. The second prototype detector is an “imaging camera detector", which employs a CCD camera and an image intensifier to take a photograph of scintillation spots of each event. With this technique, we aim at detecting the prompt and delayed vertexes with~1cm or better resolution to measure relative postion of those vertexes, by which incoming direction of anti-neutrinos can be measured. Using the prototype detector we succeeded in taking photographs of cosmic-ray muon tracks. We plan to improve this detector to detect neutron events and also to detect anti-neutrino events with directional sensitivity.