title: Photon-photon coincidences for activity determination: I-125 and other radionuclides.
abstract: Theory and experiment of photon-photon coincidence counting with distance variation for activity standardisation of radionuclide solutions are described. The activity of an I-125 solution from an international comparison organised by the BIPM in 2004 was determined. The value obtained agrees with other methods within a limit of 0.2%. The extension of this activity standardisation method to other radionuclides such as Cd-109 with I-125 as a tracer nuclide, In-111, Am-241 and I-124 with a radionuclidic impurity of I-125 is studied. Achieved uncertainties of the activities of Cd-109 and In-111 are of the order of 1.5%. The activity values of sources of Am-241 are determined relative to each other. Am-241 is used for checking the measuring system and as a long-lived reference source. After decay of the order of several I-124 half-lives, sources of I-124 with I-125 are measured to determine the I-125 activity portion.
authors.affiliation: Physikalisch-Technische Bundesanstalt, Bundesallee 100, 38116 Braunschweig, Germany. heinrich.schrader@t-online.de
authors.forename: H
authors.initials: H
authors.lastname: Schrader
mesh_terms: D000465:Algorithms; D017408:Guidelines as Topic; D038622:Internationality; D007457:Iodine Radioisotopes / Q000032:analysis*; D017785:Photons; D011834:Radiation Monitoring / Q000379:methods* / Q000592:standards*; D011868:Radioisotopes / Q000032:analysis*; D012016:Reference Values; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
chemical_list: D007457:Iodine Radioisotopes; D011868:Radioisotopes