Radiation Shielding

Prof. Igor Jovanovic has led the design of radiation shielding for the new ZEUS target areas using FLUKA and Geant4 codes.
 

All radiation-generating facilities have a legal obligation to protect their personnel from ionizing radiation. Each facility has different requirements that must be addressed by the shielding, so specific designs need to be developed and ultimately implemented. For GeV-level accelerators, several meters of radiation shielding or a beam dump combined with radiation shielding are required to reduce the radiation dose to a safe level. We developed a facility design suited for shielding of the gas target area in ZEUS, which includes an electron beam dump. The overall design goal is to limit the hourly dose to 0.02 mSv/h (2 mrem/h) and the annual dose to 1 mSv/year (100 mrem/year), according to the radiation safety regulations. The facility design is illustrated in Fig. 1, which does not display the local shielding (beam dump).

Figure 1: The overall facility design.

We conducted Monte Carlo simulations using FLUKA and validated them in Geant4. An additional validation was performed with the design of similar facility. The simulation geometry is shown in Fig. 2 and includes the optimization of the composition, thickness, and width of stacked layers of the beam dump. Representative results for the prompt dose are shown in Fig. 3. Also important to the facility design is the longer-term activation, for which the simulation was also carried out (Fig. 4).

Figure 2: (a) Simulation geometry (top view) in the Monte Carlo code FLUKA. (b) Different stacking methods are used to test the effectiveness of the radiation shielding. (c) The same simulation geometry (side view) is also defined in the Geant4 for comparison.
Figure 3: Comparison of the ambient dose equivalent between the (a) three-layer and (b) five-layer stacking configuration with the HD concrete and iron stacking. The difference between the two configurations is shown in (c) and (d).
Figure 4: Example simulation of the activation in ZEUS gas target area.

The solid target area is another major experimental area of ZEUS for which the shielding design is necessary. Preliminary designs have been developed to address the challenging environment of higher beam divergence than in the gas target area and the multi-particle environment that requires a combination of shielding materials and geometries. Preliminary FLUKA modeling is illustrated in Fig. 5.

Figure 5: Dose due to protons (top) and electrons (bottom) in the solid target area without shielding.

Read more in the publication:

T. Shi, D. Sun, I. Jovanovic, G. Kalinchenko, K. Krushelnick, C. C. Kuranz, A. Maksimchuk, J. Nees, A. G. R. Thomas, and L. Willingale, “Optimization of the Electron Beam Dump for a GeV-class Laser Electron Accelerator,” Applied Radiation and Isotopes 176, 109853 (2021).