Monte Carlo simulation of photons backscattering from various thicknesses of lead layered over concrete for energies 0.25-20 MeV using FLUKA code

Abstract

There is an increased interest in determining the photon reflection coefficient for layered systems consisting of lead (Pb) and concrete. The generation of accurate reflection coefficient data has implications for many fields, especially radiation protection, industry, and radiotherapy room design. Therefore, this study aims to calculate the reflection coefficients of photons for various lead thicknesses covering the concrete. This new data for lead, layered over concrete, supports various applications, such as an improved design of the mazes used for radiotherapy rooms, which helps to reduce cost and space requirements. The FLUKA Monte Carlo code was used to calculate photon reflection coefficients for a concrete wall with different energies. The reflection coefficient was also calculated for a concrete wall covered by varying thicknesses of lead to study the effect of lining this metal on the concrete wall. The concrete's reflection coefficient data were compared to internationally published data and showed that Monte Carlo calculations differed significantly from some of the extrapolated data. The absorbed dose of backscattered photons for various thicknesses of lead covering the ordinary concrete has been tabulated as a function of the reflection angle. Also, the reflection coefficient as a function of the Pb thicknesses covering the ordinary concrete has been figured to study the dose reduction factor. The generation of accurate data for reflection coefficients is vital for many fields, especially for radiation protection and radiotherapy room design. The new data have been presented for lead layered over concrete in various applications, such as an improvement in the design of the mazes used for radiotherapy rooms, thereby reducing the cost and space requirements. In addition, the Monte Carlo method enables calculating the energy distribution of reflected photons, and these were shown for a range of angles.

Figure 1

FLUKA Monte Carlo simulation of the ring dosimeters to calculate the dose of backscattered photons at reflection angles with respect to the incident trajectory, normal to the surface (a: is 2D and b: 3D image).

Figure 2

Comparisons between the backscattered photons of ordinary concrete of NCRP data and FLUKA calculations as a function of reflection angles (with respect to the incident trajectory, normal to the surface).

Figure 3

The fluence spectra of backscattered photons of various energy for (a): 0.5 mm, (b): 1 mm, (c): 2 mm, and (d): 4 mm Pb layered over the ordinary concrete at a reflection angle of 135°.

Figure 4

The fluence spectra of backscattered photons at various reflection angles of 2 mm Pb layered over ordinary concrete and incident photon energies of (a): 662 keV, (b): 1.25 MeV, and (c): 10 MeV.

Figure 5

The fluence spectra of backscattered photons with the various thicknesses of Pb layered over ordinary concrete at reflection angle of 135° and incident photon energies of (a): 662 keV, (b): 1.25 MeV, and (c): 10 MeV.

Figure 6

The percentage reduction factors of reflection coefficient (% RC) normalised to ordinary concrete for 2 mm Pb covering the ordinary concrete as a function of incident photons energy for variance reflection angles.

Figure 7

The percentage reduction factors of reflection coefficient (% RC) normalised to ordinary concrete for various thickness of lead covering the ordinary concrete as a function of incident photons energy. (a) at reflection angles of 105°, (b) at reflection angles of 135°, and (c) at reflection angles of 165°. represents 0.2 mm Pb, represents 0.5 mm Pb, represents 1 mm Pb, represents 2 mm Pb, represents 3 mm Pb, and represents 6 mm Pb.