The production of 177Lu for nuclear medicine at FRM-II

Two pathways exist for the production of 177Lu: thermal neutron activation of enriched 176Lu, 176Lu(n,γ)177Lu, and activation of 176Yb and its decay to 177Lu, 176Yb(n,γ)177Yb → 177Lu. The quality of the product prepared by the latter pathway depends strongly on the efficiency of lutetium separation from the ytterbium target. The direct production route was explored at FRM-II. 177Lu was produced by neutron irradiation of isotopically enriched nitrate targets prepared from 176Lu2O3 with 64.3 % enrichment. The mass of lutetium in the targets was in the range of micrograms. Irradiation times varied from hours to days. Flux densities were in the range of 1013 - 1014 ns-1cm-2. For an accurate calculation of the irradiation yield, the characteristics of the reactor must be well known, particularly the neutron temperature, which we measured. The 176Lu(n,γ)177Lu reaction yield at FRM-II was measured and a formula for calculation of the production yield was validated. The maximum achievable specific activity was estimated. The activation impurities were analyzed, the long lived 177mLu (160.5 d) confirmed as being the most serious one. The 177mLu to 177Lu activity ratio at EOB was about 0.004 % and this value is expected to increase with longer irradiation times up to about 0.015 %