Precise calibration of short-lived radioactive material is essential for nuclear medicine and power plant applications. Scientists in the NIST Radioactivity Group have developed an automated ionization chamber that they now use for that purpose. The instrument itself has been calibrated at NIST for dozens of the most important radionuclides based on NIST primary standardization methods.
This system has been developed at NIST to measure up to 100 samples with programmable sample queuing, sample handling and measurement parameters while maintaining the high precision and reproducibility of a similar manual instrument that has been used for over 30 years. Routine use of this new instrument results in reduced radiation exposure to operators, expedites the standards-transfer process and improves quality assurance. NIST has recently established calibration factors for the instrument based on primary standardizations of 18F, which is widely used for diagnostic PET imaging, and 223Ra, which is being researched as a new cancer treatment.
In addition, NIST has developed a theoretical model for the efficiency of the instrument to be used for impurity corrections and for modelling time-dependent calibration factors of decay chains.
Photo caption: NIST automated ionization chamber in action. Custom sample-holders and positioning system ensure high degree of reproducibility, lead and lead-glass shielding for safety and effectiveness, picoammeter below shielding.