A phantom for use in generating a normalization data set to be used in PET scanning (particularly integrated MR/PET scanning) is disclosed. The phantom features radiation activity distributed throughout a foam material. The foam—e.g., a polyurethane foam—may be produced by reacting two liquids, one of which is emulsified with water in which Ge68 has been dissolved. The foam produced thereby exhibits uniform distribution of radioactivity and a long mean free path for 511 keV gamma particles—two attributes that are important attributes of a PET phantom.