Development of an in vitro bioassay technique for the determination of 65Zn in Biological Samples

Abstract

The maintenance of the cyclotron in operation at the IEN-CNEN, where 123I is produced, may lead to theincorporation of 65Zn, generated by activation of the copper present in the shield, and the consequentinternal exposure of the workers. The IRD Whole Body Counter carried out about 500 in vivomeasurements, through the detection 1115 keV photons. The 123I production plant at the IEN is safe interms of radioprotection, since all positive results represent a fraction of the annual dose limitestablished by the CNEN. However, in order to improve internal monitoring of the group of workers, agamma spectrometry technique was developed at the IRD Bioassay Laboratory, aimed to thedetermination of 65Zn in biological samples. The calibration of the HPGe detection system wasaccomplished with a 65Zn liquid standard source produced and certified by the LNMRI-IRD. The sourcewas divided into two botles of 1 and 2 liters. A calibration curve of efficiency vs volume was obtainedfor each geometry in the range of 100 to 1000 mL and 1000 to 2000 mL, respectively, increasing thevolume in 100 mL steps with a 0.1 M solution of HCl. The methodology has shown to be simple, fast,and presented adequate sensitivity for its application in occupational monitoring. The minimumdetectable activity of the technique at 1 L is 5,18 Bq, which represents a Minimum Detectable EffectiveDose of 23 μSv, assuming a single incorporation of 65Zn by ingestion of a compound Type S.