Study of Extremely High Energy Cosmic Rays beyond Greisen Cut off (10^<20>eV)

秋野巨型风淋阵（AGASA）运行了12年，在格雷森上空观测到了能量为10^<20> eV的极高能量宇宙射线事件（11事件）。宇宙射线质子被认为是通过与2.7K微波背景辐射相互作用产生的介子而失去能量的。AGASA观测到的EHE宇宙射线明显超过了这个临界能量，它的性质非常有趣。在本项目中，为了确认AGASA的能量测定，我们在秋野天文台中心建立了空气荧光成像探测器（CRIS—Cosmic Ray imaging System）。在2000年和2001年，我们建立了覆盖天顶周围2个立体面的CRIS探测器和LIDAR系统来监测大气透明度。自2001年冬季以来，激光雷达系统成功运行，建立了近紫外区大气监测的宇宙射线测量目的。这一结果已经发表在《核仪器与方法》杂志上。2002年，我们在切伦科夫模式下进行了300小时的密集观测，观测了1万多个高能宇宙射线，研究了膝盖附近（10^<14 ~ >10^<16>eV）的宇宙射线能谱。

The Akeno Giant Air Shower Array (AGASA) has been operated for 12 years, then Extremely High Energy (EHE) cosmic ray events(11events) above Greisen cut off energy of 10^<20> eV were observed. Cosmic ray protons is believed to lose their energy by the pion production through the interaction with 2.7K microwave background radiation. EHE cosmic rays observed by AGASA clearly exceed this critical energy and is really interesting in its nature. In this project, to confirm the energy determination of AGASA, we have built air fluorescence imaging detector (CRIS ―― Cosmic Ray Imaging System) at the center of the Akeno Observatory.In 2000 and 2001, we have build CRIS detector which cover 2 steradian around zenith and LIDAR system to monitor atmospheric transparency. The Lidar system has been successfully in operation since the winter of 2001, and the atmospheric monitoring at near UV region for cosmic ray measurement purpose was established. This result was already published in the journal, Nuclear Instrument and Method. In 2002, very intensive observation of 300 hrs in cherenkov mode was carried out, then we have observed more than 10,000 of high energy cosmic rays and studied the cosmic ray energy spectrum around the knee region (10^<14〜>10^<16>eV).