AMBIENT DOSE EQUIVALENT RECEIVED AT 15 MV LINAC ENVIRONMENTS DUE TO PHOTONEUTRONS CONTAMINATION

Mapping of the photoneutron spectrum and flux performed at several positions over the treatment table of a 15 MV medical linac. Neutron activation technique has been applied to obtain the neutron spectra in the mixed γ -n field. Thick foils have been used due to the low neutron flux and the measurements were unfolded using the MINUIT minimizer. GEANT4 code simulations have been performed to reproduce the photoneutrons' spectrum and estimate the flux along the treatment table. The mixed radiation field around medical linear accelerator was evaluated and the variation of the ambient dose equivalent over the treatment table was estimated. Photoneutrons' ambient dose equivalent inside the irradiation field estimated as 0.56 ± 0.05 while the peripheral as 0.42 ± 0.04 mSv Gy-1. The effective dose inside the irradiation field is ranged between 0.004 and 0.049 while the peripheral up to 0.035 mSv Gy-1.