Experimental studies and nuclear model calculations on the formation of radioactive products in interactions of medium energy protons with copper, zinc and brass: Estimation of collimator activation in proton therapy facilities

Excitation functions of (p,x) processes on collimator materials for radiation therapy (Cu, Zn and brass), leading to the formation of long-lived activation products, were measured over the proton energy range 70 to 350 MeV using the stacked-foil technique. In most of the cases the product activity could be measured non-destructively via γ-ray spectrometry; for studies on low-yield products, however, radiochemical separations were essential. A comparison of the data obtained via an integration of the differential data for Cu and Zn with integral cross-section measurements on brass showed an agreement within ±17%. The experimental data for natCu, natZn and brass were also compared with theoretical data obtained using the modified hybrid nuclear model code ALICE-IPPE (1996) for intermediate energies. The agreement was found to be good up to about 120 MeV. For products rather away from the target elements, large deviations were observed. Using the measured data, an estimation of collimator activation in proton therapy facilities was done.