title: Photon sources for instrument calibration.
mesh_terms: D004601:Elementary Particles; D005453:Fluorescence; D005720:Gamma Rays; D011834:Radiation Monitoring / Q000295:instrumentation*; D011868:Radioisotopes; D011874:Radiometry; D013819:Thermoluminescent Dosimetry / Q000295:instrumentation; D014965:X-Rays
chemical_list: D011868:Radioisotopes