Excitation functions of Ge(p,xn)As reactions from threshold up to 45 MeV for production of the non-standard positron emitter As.

Nuclear reaction cross sections for the formation of As and As in proton-induced reactions on enriched Ge targets were measured up to 45 MeV utilizing three different cyclotrons at the Forschungszentrum Jülich. The stacked-thin sample activation technique in combination with high-resolution γ-ray spectrometry was used. The major γ-ray peaks of As and As formed via the Ge(p,n)As and Ge(p,2n)As reactions, respectively, were analyzed. The incident proton energy and flux on a foil were determined using several monitor reactions. Based on integrated counts, irradiation data and the nuclear decay data, the reaction cross sections were measured. All data describe the first measurements. Theoretical nuclear model calculations were then carried out by using the codes TALYS 1.96, EMPIRE 3.2 and ALICE-IPPE. A very good agreement between the measured data and calculated values was found. The new data enabled us to calculate the thick target yields and estimate the radionuclidic impurities for a given energy range. Over the optimum energy range Ep = 14 → 7 MeV, the calculated thick target yield of As amounts to 272 MBq/μAh with no As impurity at all. The Ge(p,n)As reaction on the enriched Ge is thus very suitable for clinical scale production of As at a medical cyclotron.