Speaker
Summary
Ytterbium-175 is an emerging radionuclide in the field of nuclear medicine, since it is a promising candidate for developing therapeutic agents. Despite this interest, there are still open questions about its decay properties (e.g. photon emission intensities, half-life). Furthermore, the metrological traceability to measure the activity of 175Yb accurately is yet to be established.
In this work, a successful activity standardization of 175Yb is reported. The 175Yb was obtained via the PRISMAP medical radionuclides program with the aim to derive its absolute photon emission probabilities and study its half-life. The material was produced at Institut Laue-Langevin (ILL) by neutron irradiation and went through radiochemical purification at the Paul Scherer Institute (PSI). An ampule of the received 175Yb solution was also sent to the Bureau International des Poids et Mesures (BIPM) in Paris to establish a link to the International Reference System (SIR).
Our primary choice for the activity determination method was 4πβ-γ coincidence counting, because this measurement technique has only minimal dependence on the underlying nuclear data. The measurements were realized in three different, custom-built experimental setups, taking advantage of a digitizer-based measurement approach and off-line data analysis. The activity was derived by the efficiency extrapolation method.
The activity of the solution was also measured with four liquid scintillation (LS) counters, employing the CIEMAT/NIST efficiency tracing and TDCR methods to derive its activity. Using the most recent decay data from the literature, the derived activity was consistent with the value obtained from coincidence counting. The overall standard uncertainty of the activity determination combining all results was less than 0.4%. Using the long-term LS counting data, it was possible to extract the half-life of 175Yb.
Finally, a series measurements using calibrated high purity Germanium detectors were performed in order to study the gamma spectrum of 175Yb in detail. In combination with the precisely known activity and half-life, these measurements will be used to investigate the decay scheme of 175Yb allowed and to derive absolute gamma emission probabilities in the future.
With the present work, the standardization of the novel therapeutic agent 175Yb was successfully carried out and an international traceability link was established. The half-life obtained from the long-term measurement was found to be in excellent agreement with other recent determinations. In the next analysis step, these results will be used to derive gamma emission probabilities with high precision.
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