The Auger-electron emitter¹⁶⁵Er: excitation function of the¹⁶⁵Ho(p,n)¹⁶⁵Er process

The lanthanide isotope 165 Er decays by electron capture without any accompanying gamma radiation, which makes it an ideal radionuclide for Auger electron therapy. The chemical properties of erbium with regard to labelling of bio-conjugates are virtually identical to those of radio-yttrium. We measured the excitation function of the 165 Ho(p,n) 165 Er reaction and obtained a maximum cross section of 166±20 mb at 11.1±0.5 MeV proton energy. Our findings indicate that 165 Er can be produced at any small-sized cyclotron in quantities suitable for biomedical applications. The thick target yield at E p =15 MeV is 55 MBq/μA h. A mass separated sample of the nuclide pair 160 Er/ 160 Ho was used as model to demonstrate that the separation of the 165 Er from the target matrix material Ho can be achieved by cation-exchange chromatography using Aminex A5 resin and α-HIBA as eluent in about 1 hour.