Excitation functions of natGe(p,xn)71,72,73,74As reactions up to 100 MeV with a focus on the production of 72As for medical and 73As for environmental studies

Excitation functions for the formation of the arsenic radionuclides 71As, 72As, 73As and 74As in the interaction of protons with natGe were measured from the respective threshold energy up to 100 MeV. The conventional stacked-foil technique was used and the needed thin samples were prepared by sedimentation. Irradiations were done at three cyclotrons: CV 28 and injector of COSY at Forschungszentrum Jülich, and Separate Sector Cyclotron at iThemba LABS, Somerset West. The radioactivity was measured via high-resolution γ-ray spectrometry. The measured cross section data were compared with the literature data as well as with the nuclear model calculations. In both cases, the results generally agree but there are discrepancies in some areas, the results of nuclear model calculation and some of the literature data being somewhat higher than our data. The integral yields of the four radionuclides were calculated from the measured excitation functions. The β+ emitting nuclide 72As (T1/2=26.01 h) can be produced with reasonable radionuclidic purity (71As impurity: <10%) over the energy range Ep=18→8 MeV; the yield of 93 MBq/μA h is, however, low. The radionuclide 73As (T1/2=80.30 d), a potentially useful indicator in environmental studies, could be produced with good radionuclidic purity (74As impurity: <11%) over the energy range Ep=30→18 MeV, provided, a decay time of about 60 days is allowed. Its yield would then correspond to 2.4 MBq/μA h, and GBq amounts could be produced when using a high current target.