Evaluation of an alpha probe detector for in vitro cellular dosimetry

This paper describes the design and testing of an alpha probe detector for the continuous measurement of the activity concentrations of alpha emitters in the culture media of in vitro cell suspension irradiation systems. The probe detector consists of a pen-size body housing a small silicon surface-barrier detector with a Mylar window. Theoretical calculations were performed to study the dependence of the alpha-energy spectrum on 1) the thickness of the Mylar barrier; 2) the Mylar-detector distance; and 3) the size of the detector window. These design parameters were selected by taking a compromise between the counting efficiency, the integrity of the detector, and its required range of application. The probe detector was tested using both chelated and unchelated 212Bi and 212Pb standard solutions; plate-out of these radionuclides on the Mylar barrier was observed for unchelated solutions. Alpha energy spectra were analyzed using a total integration technique. The measured activity concentrations and the calibrated values agree to within 4% for the chelated 212Bi and to within 6% for the unchelated 212Bi. The alpha probe detector can be used throughout an entire exposure time period to determine the total dose received by suspended cells, or at different time intervals to determine the dose rate in real time.