The radioisotope 90 Nb decays with a positron branching of 53% and a relatively low β + -energy of E mean = 0.66 MeV and E max = 1.5 MeV. Its half-life of 14.6 h makes it especially promising for quantitative investigation of biological processes with slow distribution kinetics using positron emission tomography. To optimise its production, the excitation functions of 90 Zr( p, xn)-processes were studied over the proton energy range of 7.5 to 19 MeV via the stacked-foil technique using both nat Zr and 99.22% enriched 90 ZrO 2 as targets. Thick target yields of 90 Nb were calculated from the measured excitation functions and were verified experimentally. The optimum energy range for the production of 90 Nb via the 90 Zr( p, n)-process was found to be E p = 17 → 7 MeV, with a yield of 600 MBq 90 Nb/µA h. The yield and radionuclidic purity of 90 Nb over the energy range of E p = 17.6 → 8.1 MeV were determined experimentally using nat Zr. At 4 h after EOB the yield of 90 Nb was found to be 290 MBq/µA h and its radionuclidic purity ≥ 95%.

Positron emitter 90 Nb / Radiochemical separation / Extraction / Ion exchange Summary. The radioisotope 90 Nb is a positron emitter with a relatively high positron branching of 51% and a rather low β + -energy of E mean = 662 keV (E max = 1.5 MeV) with potential for application in positron emission tomography (PET). Its half-life of 14.6 h makes it especially promising for the quantitative investigation of biological processes with slow distribution kinetics. An advantageous production route of 90 Nb is the nat Zr( p, n) 90 Nb process. To separate nca (nocarrier-added) radioniobium from macroscopic amounts of irradiated zirconium targets, an effective two step separation procedure was developed. A liquid-liquid extraction using N-benzoyl-N-phenylhydroxylamine (BPHA) in CHCl 3 was applied first to separate the bulk of the zirconium matrix with a Zr separation coefficient of about 10 4 , followed by anionexchange chromatography for high grade purification of nca radioniobium. A sufficiently high decontamination factor of > 2 × 10 7 and an overall radiochemical yield of nca 90 Nb of about 70% was achieved within about 3 hours.

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