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Description
In nuclear medicine, the positron emitting $^{86}$Y (14.7 h) is an emerging imaging isotope for use in combination with the $\beta$$^-$ emitting therapeutic radionuclide $^{90}$Y (2.7 d), the pair being commonly called as a matched theranostic pair [1]. To produce the radionuclide $^{86}$Y via the $^{86}$Sr(p,n) reaction in a pure form, 96.4% enriched thin $^{86}$SrCO$_3$ targets were irradiated with protons of energies 7 and 8 MeV at BC1710 cyclotron, Forschungszentrum Jülich (FZJ), Germany. We have determined the positron emission probability P$_\beta$$^+$ in the $\epsilon$+$\beta$$^+$ decay of $^{86}$Y (14.7 h) by measuring the 511 keV annihilation $\gamma$-ray using an ORTEC HPGe detector. During counting, each irradiated $^{86}$SrCO$_3$ sample was placed inside a circular groove (diameter 1 cm, depth 0.01 cm) of a Cu disk (diameter 3 cm, height 0.5 cm) and covered with another one of the same type and size. The Cu enclosure served to annihilate almost all $\beta$$^+$ particles in $^{86}$Y decay, Q$^+$($^{86}$Y)=5.24$\pm$0.01 MeV, within its geometric volume. Several corrections were made including that for the counting geometry to deduce the final results. The electron capture probability P($\epsilon$+$\beta$$^+$) has also been determined as an additional check, since %P($\epsilon$+$\beta$$^+$)=100, by measuring the K$_\alpha$ and K$_\beta$ X-rays of energies 14.1 and 15.8 keV, respectively, using a special ORTEC HPGe detector, with a 0.3 mm thick Be window, for low-energy $\gamma$-rays. The positron emission and electron capture probabilities are determined to be 27.6$\pm$1.4% and 72.2$\pm$4.0%, respectively. The normalization yields %P$_\beta$$^+$=27.7$\pm$1.5 and %P$\epsilon$=72.3$\pm$1.5. The positron emission probability of this work is found to be in good agreement with the value 27.9$\pm$1.2% [2], deduced using the newly constructed $\gamma$-decay/level-scheme of $^{86}$Sr and calculation of electron capture to positron decay ratio for each beta feeding levels, and is lower by 14% compared to the latest evaluated value of 32.5$\pm$2.0 [3], obtained using the prior $\gamma$-decay/level-scheme of $^{86}$Sr and the same method of Ref. [2]. The deduced electron capture probability of the present work provided an additional confirmation for the measured positron emission probability of $^{86}$Y.
References:
1.F. Rösch, H. Herzog, and S. M. Qaim, Pharmaceuticals 10, UNSP article 56 (2017).
2.A. C. Gula, E. A. McCutchan, C. J. Lister, J. P. Greene, S. Zhu, P. A. Ellison, R. J. Nickles, M. P. Carpenter, S. V. Smith, and A. A. Sonzogni, Phys. Rev. C 102, 034316 (2020).
3.A. Negret and B. Singh, Nuclear Data Sheets 124, 1 (2015).