A novel method to estimate the thickness of the depletion layer of an X-ray CCD

We present a new method for estimating the thickness of the depletion layer of an X-ray CCD without a calibrated X-ray source. It is known that a high-energy particle continuously loses its energy when it passes through a material, and that its total-energy loss in a thin material depends on the thickness of the material. We irradiated a Hamamatsu-CCD (CCD-CREST Deep 1) with a conversion β-ray source 207Bi which emits monoenergetic β-rays, then obtained an energy-loss distribution. In comparison with an energy-loss distribution simulated with Geant4, we found that the CCD-CREST has a depletion layer thickness of ∼6.7 μm, which is consistent with the result using a calibrated X-ray source. Since it is difficult to obtain a calibrated X-ray source, our method is useful for estimating a depletion layer thickness.