A Methodology to estimate and minimize neutron dose rates received by occupationally exposed individuals at IEN/CNEN cyclotron facilities

摘要

In 1999/2000, a methodology for shielding evaluation and calculation for one of the CV-28 cyclotrontargets, namely the Iodine production system KIPROS, designed in Karlsruhe, began to be developed. Theneutron spectrum at the Iodine production room has been surveyed through neutron activation analysis (NAA).The resulting data were used as the input of a shielding calculation program, the ANISN500, in order to obtain amore efficient shielding for this target room. In December 2002, the Instituto de Engenharia Nuclear (IEN), aunit of the Brazilian nuclear regulatory commission, Comiss?o Nacional de Energia Nuclear (CNEN), acquired anew cyclotron, the RDS111, from CTI, in order to produce short half-life radioisotopes. Thus, since 2003, thereare two cyclotrons in operation: the CV-28, an old model from TCC, and the new one mentioned above. Sincethen, we have been increasing our radiopharmaceutical production for medical diagnosis purposes. Because ofthe increasing production, a methodology to reduce dose rates during cyclotron operations had been developed.The purpose of this work is to present a methodology to estimate neutron doses at KIPROS and fluorine-18targets of CV-28 and RDS111 cyclotron accelerators in order to minimize the dose rates received byoccupationally exposed individuals during irradiation processes. The methodology includes the survey of theneutron energy spectra generated at these cyclotron targets using neutron activation analysis. These results arethen used to create a Monte Carlo computational model in order to improve the shielding and to reduce neutrondoses at our cyclotron complex facilities so as to conform to the ALARA principle.