A method is disclosed for determining radiation attenuation as a result of an object in a positron emission tomography scanner. In at least one embodiment, a phantom object is arranged in the positron emission tomography scanner during the method. First raw radiation data of the phantom object is acquired while the object is not arranged in the positron emission tomography scanner. A first image of the phantom object is calculated from the first raw radiation data. The object then is arranged in the positron emission tomography scanner (2) and preliminary radiation attenuation of the object is identified. Second raw radiation data of the phantom object is acquired while the object is arranged in the positron emission tomography scanner. A second image of the phantom object is calculated from the second raw radiation data taking into account the preliminary radiation attenuation. The radiation attenuation is determined on the basis of the first image and the second image.