Sensitivity evaluation of well-type ionization chamber:A tool to manage spent radioactive sealed sources

Abstract

Spent radioactive sealed sources (SRSS), after used in medicine, industry and research, are sent as radioactive waste to one of the National Nuclear Energy Commission (CNEN) Institutes. Radioactive Waste Management Laboratory (RWML) of the Nuclear and Energy Research Institute – IPEN-CNEN/SP, among its functions, is responsible for receiving, treating and storing radioactive wastes generated in all research centers of the IPENCNEN/SP, as well as from other Brazilians institutions. The process of treatment adopted for SRSS is the withdraw the source from its original shield and transfer it to a standard shield. An important step of this process is the characterization of the radioactive source. Generally, dose calibrators, commonly used in nuclear medicine services (NMS), are used to carry out this task. Considering that the radionuclides and the geometries of the sources to be characterized are different from those used in NMS, it is necessary to evaluate the sensitivity of this equipment for these kinds of SRSS activity measurements. This study was developed using commercial standards sources and sources with known activities under responsibility of the RWML, amongst those, 241Am and 147Pm sources were studied. The results indicate that the sensitivity of the chamber follows typical standard of punctual sources geometry. However, for other sources there are differences due to the effect of the source geometry. In such a way what one can find is the regions of higher sensitivity for those kinds of sources, with acceptable error and confidence level for this end.