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[43.31] Beta-ray Diagnosis of Charge-Coupled-Devices

S. Kitamoto, M. Ohta, T. Okada, T. Kohmura, Koji Mori (Osaka University), H. Awaki, K. Tachibana (Ehime University)

We will report an experiment for beta-ray diagnosis of charge-coupled-devices (CCDs). A CCD was exposed to beta-rays (976 keV and 1048 keV) from ²⁰⁷Bi radio isotope. The incident angle of the beta-rays is fixed to be a grazing incident. The electron-hole pairs are created according to the track of the beta-rays. Thanks to the good imaging capability of the CCD, two dimensional projection of the beta-ray track onto the CCD surface can be detected. Also the charge spread by diffusion of the electrons is measurable. Since the range of electrons with energy of ~1 MeV is ~2 mm, majority of the electrons go through with a straight track in the interesting layer. Therefore the depth of the secondary electrons created by the beta-ray can be determined from the geometry, and we can find the charge spread as a function of depth of the secondary electrons. In the depletion layer, the electric field is strong and the diffusion of the electrons is small. Below the depletion layer, the electric field is weak, and the electrons diffuse out. Thus the thickness of the depletion layer can be derived form this measurement. We will present some results from this measurement.