Experimental characterization of the neutron spectra generated by a high-energy clinical linac using neutron activation metal detectors

Abstract

Introduction Electron linacs accelerate high-energy electron beams to impinge on high Z targets producing bremsstrahlung photons. Due to high operational energy of this type of linacs a significant number of neutrons are created by (γ,n) reactions. Purpose The main objective of this work is to report the results of an experimental characterization of the neutron spectra generated by a high-energy clinical LINAC. The photoneutron contamination of an ELEKTA is investigated in detail in its 15 MV photon mode. Materials and methods We developed a technique for neutron dosimetry based on neutron activation of different metal detectors. This system offers the possibility to measure neutrons over a wide energy range at intense and complex mixed n–g fields. To obtain the neutron spectrum from the activation technique, measurements must be unfolded. A method for unfolding the neutron energy spectra has been developed using the Minuit minimization. Results The unfolded procedure reproduced reasonably well the physical expectation of two peaks in the spectrum. Both peaks are located in the correct energy region; from 1e-8 to 1e-6 MeV the thermal component and from 0.05 to 1 MeV the fast. The fast part of the spectrum gives two peaks at energies of 0.1 and 0.8 MeV. The thermal peak corresponds to the 15% of the total neutron fluence and the fast component covers ∼70% of the neutron spectrum. Conclusion The unfolded procedure using the Minuit minimization reproduced reasonably well the physical expectation of two peaks in the spectrum.