Secondary standard instrumentation used at NMISA for activity measurement

This paper aims to inform the public and scientists not in the field of radioactivity on the way secondary activity measurements are undertaken at NMISA to ensure the quality of life of South Africans. Various secondary standard nuclear instruments are used for routine activity measurements for dissemination to the user community such as the nuclear medicine industry. Three instrument types are discussed, namely the ionization chamber, high-purity germanium (HPGe) detectors and a commercial liquid scintillation (LS) analyzer. Most modern hospitals have nuclear medicine facilities where patients ingest radioactive medicine to diagnose and treat various forms of cancer. Using an ionization chamber (commonly known as a dose calibrator), hospitals can measure the dose of radioactivity to the required accuracy. NMISA can ensure that the dose calibrators used by these hospitals provide accurate measurements by performing stability checks using radioactive standards, thereby ensuring that patients receive the correct dose. In addition, NMISA undertakes activity measurements of shortlived radionuclides on its secondary standard ionization chamber for isotope production facilities. Because this ionization chamber has lower gas pressure than that normally produced by the manufacturer, the paper focuses much attention on explaining a normalization scheme devised to allow NMISA to make use of the manufacturer’s supplied calibration factors. Where environmental radioactivity and possible radioactivity in consumer products are a concern, NMISA can carry out low level gamma-ray spectroscopy measurements on the samples and products, using HPGe detectors, to ensure that they are safe and below the legal acceptable radioactivity limit. For samples containing pure beta-emitters such as 3 H, 14 C and 90 Sr, a LS analyzer is used.