Fig. 1. Structure diagram of the irradiator with triple screen functionality (color online)(a) Layout of the overall structure, (b) Top view of the scattering chamberA‒Out screen, lead; B‒Source cylinder, lead; C‒Source shell, aluminum; D‒Scattering chamber, tungsten alloy; E‒Primary collimator, tungsten alloy; F‒Secondary collimator, tungsten alloy

Fig. 2. Illustration of the influence of the scattering chamber on the beam (color online)

Fig. 3. Spectrum optimization by the scattering chamber (a) Energy spectrum with or without the scattering chamber, (b) Energy spectra for different wall materials

Fig. 4. Definition of source cylinder rotation from the side view of the irradiator (color online)

Fig. 5. Definition of the primary collimator rotation from the top view of the irradiator (color online)

Fig. 6. Beam shielding function of the irradiator (a) Calculations for the source cylinder, (b) Calculations for the primary collimator

Fig. 7. Circular geometry for investigating the planar dosimetric properties

Fig. 8. Ratio of air kerma per solid angle in the circular regions against the central ring

Fig. 9. Spectra and total fluences in the circular regions (color online) (a) Spectra per solid angle in circular regions, (b) Ratio of total fluence per solid angle in the circular regions against the central ring

Fig. 10. Air kerma per solid angle (relative values) for distances between 50 cm and 500 cm from the radioactive source

Fig. 11. Comparison between the ⁶⁰Co γ spectrum obtained in this work and corresponding results from the Ref.[5]