From Particle-Production Cross Sections to KERMA and Absorbed Dose for the Case 96 MeV n-12C Interactions

University dissertation from Uppsala : Acta Universitatis Upsaliensis

Abstract: Neutron-carbon interactions have been studied with a focus on charged-particle production of relevance to radiation protection and medical applications, such as cancer therapy. The measurements have been performed using the particle-detection setup, MEDLEY, and the 96 MeV neutron beam at the The Svedberg Laboratory in Uppsala.Double-differential cross sections of inclusive charged-particle production are compared with recent calculations from models based on the GNASH code including direct, preequilibrium and compound processes. For protons, the shapes of the cross-section spectra are reasonably well described by the calculations. For the other particles- d, t, 3He and ?- there are important discrepancies, in particular for 3He-ions and ?-particles, concerning both shape and magnitude of the spectra.Using the new cross sections, partial as well as total KERMA coefficients have been determined. The coefficients have also been compared to previous experimental results and model calculations. The p, d and t KERMA coefficients are in good agreement with those from a previous measurement. For the helium isotopes, there are no previous measurements at this energy. The KERMA coefficients are considerably higher (by up to 30%) than those predicted by the calculations.The KERMA results indicate that protons and ? -particles are the main contributors to the dose. A 6x6x6 cm3 carbon phantom, exposed to a broad and a pencil-like beam, is used for the computation of the absorbed doses deposited by these two particles in spheres of 1 ?m in diameter, located at various positions in the phantom. The maximum doses are deposited at ~3 cm from the surface of neutron impact for protons and within 1 cm for ?-particles. For the pencil beam, deposited doses are spread over regions of ~1.5 cm and ~300 ?m transverse to the beam for protons and ?-particles, respectively. The results are consistent with previous integral measurements at lower energies.