Speaker
Description
Terbium is unique for medical applications since different Tb isotopes emit $\alpha$, $\beta^-$, $\beta^+$ or $\gamma$-radiation or conversion and Auger electrons respectively. In particular, the quadruplet of Tb isotopes $^{149}$Tb, $^{152}$Tb, $^{155}$Tb and $^{161}$Tb can cover together all diagnostic and therapeutic modalities in nuclear medicine [1]. Their identical chemical and biochemical properties assures fully exchangeable in vivo behavior.
While the neutron-rich $^{161}$Tb is reactor-produced, the neutron-deficient Tb isotopes are accelerator-produced, mainly by (p,x n) reactions on enriched Gd targets or by spallation of Ta targets combined with on-line or off-line isotope separation at CERN-ISOLDE or CERN-MEDICIS respectively [1-5].
Due to the relatively low volatility of trivalent lanthanides, the Ta target and the ionizer line have to be kept at high temperature. Dysprosium is more easily released than terbium, therefore at ISOLDE the collections of Tb isotopes are performed indirectly, by resonantly laser ionizing the Dy precursor isotopes. However, there is considerable background of surface ionized isobars and ``pseudo-isobars’’ of oxide sidebands. The latter can actually dominate the overall activity and dose rate of collected samples and should be minimized to limit the personal dose during handling, transport and chemical separation of the collected Tb samples.
On-line measurements with the ISOLTRAP multi-reflection time-of-flight mass spectrometer (MR-ToF MS) [6,7] and off-line $\gamma$-ray spectrometry of collected test samples were used to characterize the beam composition at masses 149, 152 and 155 as function of target temperature, ionizer temperature and laser settings respectively.
[1] C. Müller et al., J. Nucl. Med. 53 (2012) 1951.
[2] G.J. Beyer et al., Radiochim. Acta 90 (2002) 247.
[3] R. Formento Cavaier et al., Phys. Procedia 90 (2017) 217.
[4] U. Köster et al., Nucl. Instrum. Meth. B 463 (2020) 111.
[5] C. Favaretto et al., EJNMMI Radiopharm Chem. 6 (2021) 37.
[6] R.N. Wolf et al., Int. J. Mass Spec. 349-350 (2013) 123.
[7] S. Kreim et al., Nucl. Instrum. Meth. B 317 (2013) 492.
