Activation cross sections of the 169Tm(d,2n) reaction for the production of the therapeutic radionuclide 169Yb

The radionuclide 169Yb (T1/2 = 32.0 d, EC = 100 %) is almost a pure Auger electron and X-ray emitter and has been gaining interest in brachytherapy. Today large scale production of 169Yb is done via the (n,γ) reaction on 168Yb of low isotopic enrichment at nuclear reactors. This production route yields a product of low specific activity in case of natural Yb target or of higher specific activity in the case of highly enriched 168Yb target but no-carrier-added product. Therefore, alternative production routes utilizing charged particle induced processes on the monoisotopic target 169Tm or stable isotopes of erbium appeared to be interesting. Investigation of the excitation function of the (p,n) nuclear reaction on Tm was requested by an IAEA Coordinated Research Project on Nuclear Data for Production of Therapeutic Radionuclides. Recently new results on the 169Tm(p,n) route were reported and a critical comparison with the reactor method of production was presented. The aim of the present work was to perform a detailed study of the excitation function of the 169Tm(d,2n)169Yb process and to compare the production yield with the (p,n) and the reactor based methods. Our systematic studies on deuteron induced nuclear reactions shows that in the heavy mass region the (d,2n) process is more productive compared to the (p,n) reaction, therefore the 169Tm(d,2n) reaction was also introduced in the IAEA CRP. For this reaction no earlier experimental results were found in the literature. The excitation function was measured by the stacked-foil technique. The thulium oxide targets (prepared using the sedimentation technique) were stacked with Ti monitor foils. Complete excitation function was measured for the used natTi(d,x)48V beam monitor reaction. Irradiations were done at the external beam of the CGR 560 cyclotron of the VUB and of the MGC 20E cyclotron of ATOMKI at incident energies of 20.6, 15.4, 10.0 and 8.0 MeV, allowing reliable determination of cross sections for the production of 169Yb from the threshold up to 21 MeV. The measured cross sections were compared with the theoretical effective cross sections calculated by using the computer code ALICE-IPPE. First calculations were carried out without any parameter adjustment, i.e. by applying the standard input parameters. Significant systematic disagreement was found, indicating the need for parameter change. Thick target yields calculated from our fitted cross section values show very significant yield increase over the proton-induced reaction in the optimal energy range. However, the yield is still much lower than in reactor production. (author)