EVALUATION OF AN ALPHA-PROBE DETECTOR FOR INVITRO CELLULAR DOSIMETRY

This paper describes the design and testing of an alpha probe detector for the continuous measurement of the activity concentrations of alph a emitters in the culture media of in vitro cell suspension irradiatio n systems. The probe detector consists of a pen-size body housing a sm all silicon surface-barrier detector with a Mylar window. Theoretical calculations were performed to study the dependence of the alpha-energ y spectrum on 1) the thickness of the Mylar barrier; 2) the Mylar-dete ctor distance; and 3) the size of the detector window. These design pa rameters were selected by taking a compromise between the counting eff iciency, the integrity of the detector, and its required range of appl ication. The probe detector was tested using both chelated and unchela ted Bi-212 and Pb-212 standard solutions; plate-out of these radionucl ides 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 w ithin 4% for the chelated B-212 and to within 6% for the unchelated Bi -212. The alpha probe detector can be used throughout an entire exposu re time period to determine the total dose received by suspended cells , or at different time intervals to determine the dose rate in real ti me.