Telescope for observation of cosmic ray isotopes

The dE/dx x E telescope is usually employed for the observation of cosmic ray isotopes. It is effective for particles whose atomic numbers are 4 or less, but it is only used to determine their chemical composition for particles whose atomic numbers are 5 or more. However, it has been made clear by calculation that the isotopes near iron may be separated if a large, high resolution solid-state detector is used. Among the factors to determine the accuracy of particle measurement, the oblique incidence to the detector affects it most as the atomic number of the particle to be discriminated increases. To eliminate this effect, the dE/dx x E telescope with large effective solid angle is being planned by adopting two circular (x-y) position detectors for incidence angle correction. Four electrodes are required to obtain two position signals from a circular solid-state detector. With the form of these four electrodes being point, the linearity of position signals at distant points from x and y axes are poor. Since the change of electrode form is necessary for improving the linearity, simulation experiments have been carried out using an electrolytic tank. A position detector of 70 mm diameter with 90 degree electrodes, that showed the best result, has been produced for trial, and the performance was tested. Isotopes near 56Fe, not to speak of 12C, 13C, can be separated with good statistical accuracy, because a telescope of high resolution in large solid angle is obtained as stated above. (Wakatsuki, Y.)