Phantom, radiation imaging device, and correction method for photon counting detector

The invention provides a phantom, a radiation imaging device, and a correction method for a photon counting detector, which can shorten the time required for acquiring correction data even in a large irradiation field. A phantom used when acquiring correction data for a photon counting detector that outputs an electric signal corresponding to photon energy of incident radiation, the phantom including a first substrate material and a second substrate material as known materials, the first substrate material having a smaller attenuation coefficient with respect to the radiation than the second substrate material, and the second substrate material having a smaller attenuation coefficient with respect to the radiation than the first substrate material. The thickness of the radiation beam varies in steps in a direction orthogonal to an irradiation field of the radiation beam, and the thickness of the radiation beam varies as the distance from the center of the irradiation field increases in each step in a directio