Optimal shielding design for bunkers of compact cyclotrons used in the production of medical radionuclides.

Purpose: There are several options to consider in the design of a vault that will house a cyclotron for radioisotopes production with regards to the door entrance. Alternatives are a direct-shielded door, a simple maze, or a double-legged maze. In this work, the impact of the neutron and photon doses at the vault entrance was evaluated for these options.

Methods: Monte Carlo simulations were carried out in order to assess photon and neutron ambient dose equivalents. Simulations results were compared to experimental measurements taken inside a vault with a direct-shielded door.

Results: The double-legged maze is the configuration that provides the higher degree of radiological protection at the vault entrance. In addition, the fact of the location of the cyclotron target plays an important role in the ambient dose equivalents.

Conclusions: The comparison performed between measurements and results of MCNP simulations confirmed a favorable agreement; maze legs reduce the neutron energies at the entrances of the vault. However, a degree of dose reduction similar to the one obtained for a two-legged maze can be achieved with the addition of shielding against neutrons in the inner maze entrance to act as a second door. A choice of a vault design is more evident by comparing the results of this study.