Calibration of HPGE detector for assay of 131I labeled radio chemicals

Full text: Large numbers of radio chemicals are prepared for the use in medicines for the preparation of radiopharmaceuticals for human consumption. These radio chemicals are prepared from 131I prepared by neutron irradiation of tellurium in a reactor. 131I and various radio chemicals such as NaI, NaIO3 and elemental iodine are regularly produced for use in medicine. 131I so produced is checked for radio nuclide purity by gamma ray spectrometry using HPGe detector. Detector calibration is carried out using various standards. However gamma emitting isotopes 241Am, 114mIn, 203Hg, 60Co, and 137Cs were short listed for calibration of the instrument based on gamma energy, single photon emission, region of interest and availability. The detector shows a consistent efficiency for all the standards. Secondary peaks due to fluorescence from filter and shielding material lead were reduced by combination of tin, copper and aluminum. Quality of primary radiochemical was determined based on consideration of impurity levels of long lived isotopes. In most of the cases, the radionuclide purity of the chemicals was found to be within the acceptable limits