Development of a front detector for reactor neutrino oscillation experiments

我们为中微子振荡实验装置“KarnLAND”的前探测器研制了新型反中微子探测器技术。在包括KamLAND在内的液体闪烁体装置中，延迟符合技术对降低本底有很强的作用。然而，前端探测器应该测量反应堆附近的读取器反中微子谱，以了解中微子谱没有振荡，应该在地面附近工作，而不是在地下深处，那么即使延迟符合也不能拒绝所有由地面大通量宇宙射线伪造的背景事件。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探测器。我们制作了以下两个原型探测器。第一种是分段检测器。使用该检测器，我们确认，顶点的位置分辨率提高到几厘米。利用这种高分辨率，可以利用真实的和假的快中子事件的顶点拓扑结构的差异，区分出假的缓发符合事件和真实的反中微子事件。我们计划把这个原型探测器放在任何一个反应堆的前面。第二个原型探测器是一个“成像照相机探测器”，它采用了一个CCD照相机和一个图像增强器来拍摄每个事件的闪烁点的照片。通过这项技术，我们的目标是以~1cm或更好的分辨率检测即时和延迟顶点，以测量这些顶点的相对位置，从而可以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子轨道的照片。我们计划改进这一探测器，以探测中子事件，并探测反中微子事件的方向灵敏度。

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.