Development of an air shower array for accurate determination of the arrival direction of cosmic rays in the 10^<15>eV region.

1986年构建的阵列于1987年更新，有最终系统用于测试实验，如以下： 16个快速计时探测器放置在一个4x 4矩阵中，与1500万分离。每个consists of a plastic scintillater of 500 x500 x35 size and a fast photomultiplier accomodated in a steinless stealbox of whcih inner surface是painted white。一个0.5厘米厚的板被放置在盒子的顶部，以便有更好的时间分辨率通过转换高能伽马射线进入选择对。一个摄像头系统被用于收集数据，而这些数据被微型计算机控制。数据被记录在光学磁盘上，频率约为1赫兹。在添加到这些内容中， 8个探测器被分配到阵列的中心和外围部分。测试实验的两个主要目的，一. E，1）在很长一段时间内建立稳定性（特别是在恶劣天气条件下），2）获得更好的增强分辨率，然后取得了成功。角度分辨率是估计的，它取决于淋浴尺寸、探测器的数目和探测器的定时准确性。当前系统give-0.7 for 10^<15>eV cosmic？where means that the estimated arrival direction falls in within from the true direction for 50%cases。Increasing the number of detectors and upgrading the quality of scintillaters will give us better resuolution than the present one<14><15>; better than 1 for 10^ eV region showers better than 0.3 for 10^ eV showers。Thus we have established the basis for a full scale experiment at Yambatin （4300 m） in Tibet and expect that a reliable gamma-ray astronomy in the 10^ eV region can be explored<15>。

The array constructed in 1986 has been updated in 1987 to have the final system used for test experiment as follows: 16 fast timing detectors are placed in a 4x4 matrix with 15 m separation. Each consists of a plastic scintillater of 500x 500x35 size and a fast photomultiplier accomodated in a steinless steal box of whcih inner surface is painted white. A lead plate of 0.5 cm thick is placed on the top of the box to have better time resolution by converting high energy gamma rays into election pairs. A cammac system is used for the data taking which is controlled by a micor-computer. The data is recorded in an optical disk with a frequency of about 1 Hz. In addition to these, 8 detectors dedicated to the electron number measurement are distributed in the center and peripheral part of the array.The two main purposes of the test experiment, i.e., 1) establishing the stability for a long time (especially for heavy weather conditions) and 2) acquiring the augular resolution better then 1゜, have been achieved successfully. The angular resolution is estimated and its dependence on the shower size, the number of detector and the timing accuracy of the detectors has been clarified. The present system give -0.7゜ for 10^<15>eV cosmic rays where means that the estimated arrival direction falls in within from the true direction for 50 % cases. Increasing the number of detectors and upgrading the quality of scintillaters will give us better resuolution than the present one; better than 1゜ for 10^<14>eV region showers better than 0.3゜ for 10^<15>eV showers.Thus we have established the basis for a full scale experiment at Yambatin (4300m) in Tibet and expect that a reliable gamma-ray astronomy in the 10^<15>eV region can be explored.