Characterization of a 137 Cs standard source for calibration purposes at

Radiation protection monitoring instruments should be calibrated by accredited calibration laboratories. To offer calibration services, a laboratory must accomplish all requirements established by the national regulatory agency. The Calibration Service of the Centro Regional de Ciências Nucleares (CRCN-NE), Comissão Nacional de Energia Nuclear, Recife, Brazil, is trying to achieve this accreditation. In the present work, a Cs standard source was characterized following the national and international recommendations and the results are presented. This source is a commercially available single source irradiator model 28-8A, manufactured by JLShepherd & Associates, with initial activity of 444 GBq (05/13/03). To provide different air kerma rates, as required for the calibration of portable radiation monitors, this irradiator have a set of four lead attenuators with different thickness, providing attenuation factors equal to 2, 4, 10 and 100 times (nominally). The performed tests included: size and uniformity of the radiation standard field at calibration reference position, variation of the air kerma rate for different lead attenuators, determination of attenuation factors for each lead attenuator configuration, and determination of the radiation scattering at the calibration reference position. The results showed the usefulness of the Cs standard source for the calibration of radiation protection monitoring detectors.