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.

The effects of the Brazilian regulatory inspection programme on nuclear medicine facilities.

This paper aims to demonstrate the importance of the regulatory inspections carried out by the Brazilian regulatory body in the area of nuclear medicine. The main aspects observed during the inspections are presented as well as the time evolution of the non-compliances, according to their occurrence by type. We also evaluate factors concerning the working of the nuclear medicine facility responsible for solving the non-compliances. The results suggest a decrease of occurrence of non-compliances with time that can be related to the strictness of the inspections and the awareness of the personnel in the nuclear medicine facilities. An analysis of radiation dose exposure levels for the professionals involved in nuclear medicine was carried out; although dose values are below regulatory dose limits, their occurrence is not decreasing satisfactorily. Results indicate the need for staff training and commitment of the responsible nuclear medicine facility staff to the radiological protection procedures. Our results also emphasise the importance of continuous coercive actions to improve the level of radiological protection in nuclear medicine facilities in compliance with the standards established by the national regulatory authority and international recommendations.