Effect of X-ray energies on induced photo-neutron doses

Abstract

Photoneutrons induced by two high energies range from the Elekta medical linear accelerator (10 and 18 MV) were measured by nuclear track detectors (NTDs). CR-39 NTD in contact with converter screen slide films, natural boron of thickness 40 μm coated on the polyester film (BN1). Detectors were exposed at 100 cm SSD with field size 20×20 on the patient table, with chest phantom and with build-up Perspex used for high-energy exposure. CR-39 registers the thermal neutron by the (n–α) reaction with the thin layer of boron and the fast neutron was measured through the (n–p) elastic scattering with the H₂ molecules in the CR-39 constituents.It was found that the total neutron dose (thermal and fast) from the 18 MV X-ray is higher than that of 10 MV. The measured thermal neutron dose is relatively smaller than the fast neutron dose in the case of direct exposure at the two X-ray energies. On the other hand, in the case of measurements on phantom and upon the use of build-up Perspex sheets, the ratio of fast to that of thermal is less than that of direct exposure.

Keywords:

• photoneutrons
• high-energy photons
• BN1 converter film
• dosimetry
• NTDs

Acknowledgements

The authors would like to express their deep thanks and appreciation to Prof. Dr A. Hussein, Professor of Radiation Physics, Faculty of Science, El Menofiya University, for his valuable advice and fruitful discussions.