Measurement of absolute activation cross sections from carbon and aluminum for proton therapy

Abstract This experimental study aims to measure nuclear cross sections from nat C and 27 Al which serve as reference targets regarding radioactivation in proton therapy. Graphite and aluminum foils were activated in broad, quasi-monochromatic proton fields generated with the pencil-beam scanning technique. The γ -emissions were analyzed subsequently in a nearby γ -ray spectrometry facility designed for low-level radioactivity measurements. The number of incident protons was measured with a Faraday Cup. A detailed evaluation of the uncertainties was performed. The cross section for the nat C(p,x) 11 C reaction at 100 MeV is (70.2 ± 1.6 (sys.) ± 0.2 (stat.)) mb. The production cross sections from 27 Al at 100 MeV are (19.9 ± 0.4 ± 0.3) mb for 22 Na and ( 11.5 ± 0.3 ± 0.1 ) mb for 24 Na. The systematic uncertainties contribute 2.0%–2.4% of the quoted uncertainties ( k = 1 ) of cross sections. Concluding, radioactivation cross sections were measured with proton fields in a clinically commissioned environment. The measured activation cross sections from aluminum used for monitoring of the proton fluence agree with the averaged values compiled in nuclear reaction data bases. For proton-induced radioactivation from carbon the chemical purity of the target strongly affects the experimental results. The cross section for the production of 11 C derived from a measurement with a high-purity graphite target is in line with the largest cross section obtained in prior studies.