Development of 137Cs irradiation facility for metrological application

Abstract

In this work, 137Cs irradiation facility at the National Institute of Standards (NIS) was developed to enhance the calibration processes. Different thickness lead sheets were used for beam attenuation, to enlarge the 137Cs dose range. Ambient dose equivalent rate, H∗(10) was measured using two ionization chambers at a different source-detector distances (SDDs) and a lead sheet thickness. The deviation from the inverse square law for the dose.SDD relationship was obtained. The beam flatness of unattenuated and the lead attenuated beam was measured. The attenuation coefficient for the used lead sheets was obtained and correlated to the broad beam geometry. The room scattering was studied in detail. The uncertainty of the measured doses was calculated. It was found that the inverse square law is verified well at SDD.2m. The measured attenuation coefficient for lead attenuators is affected by the broad beam geometry. The contribution of the scattering component of the dose at a certain SDD is the major source of uncertainty since it extracted a value of 1.05%, while the combined uncertainty from all other factors affecting the dose measurements is 1.34%.