A solution containing 68Ge in equilibrium with its daughter, 68Ga, has been standardized for the first time at the National Institute of Standards and Technology using 3 liquid scintillation- based techniques: live-timed 4pb-g anticoincidence (LTAC) counting , the Triple-to-Double Coincidence Ratio (TDCR) method, and 3H-standard efficiency tracing with the CIEMAT/NIST method. The LTAC technique is much less dependent on level scheme data and model-dependent parameters and was thus able to provide a reference activity concentration value for the master solution with a combined standard uncertainty of about 0.3%. The other two methods gave activity concentration values with respective differences from the reference value of +1.2% and -1.5%, which were still within the experimental uncertainties. Measurements made on the NIST 4p"g secondary standard ionization chamber allowed for the determination of calibration factors for that instrument, allowing future calibrations to be made for 68Ge/68Ga without the need for a primary measurement. The ability to produce standardized solutions of 68Ge presents opportunities for the development of a number of NIST-traceable calibration sources with very low uncertainties (<1%, k=1) that can be used in diagnostic medical imaging.
Citation: Journal of Research (NIST JRES) -
NIST Pub Series: Journal of Research (NIST JRES)
Pub Type: NIST Pubs
anti-coincidence, efficiency tracing, gallium-68, germanium-68, liquid scintillation counting, standardization, triple-to-double coincidence ratio method