A 244Cm irradiator for protracted exposure of cultured Mammalian cells with alpha particles

A 244Cm alpha-particle irradiator was designed and constructed for radiobiological studies where protracted exposure at a low dose rate of cultured mammalian cells is required. It allows irradiation of a cell monolayer attached to the Mylar bottom of a specially designed Petri dish of 56 mm diameter (approximately 25 cm(2) area). The irradiator is based on a 20-mm-diameter stainless steel chamber containing a 148 kBq 244Cm source. The chamber, flushed with helium gas at a pressure kept slightly above the external pressure, is inserted into a cell incubator where temperature and CO2 concentration are controlled. Spectrometric and dosimetric characterization of the irradiator was carried out by means of an ion-implanted-silicon charged-particle detector, CR39 detectors, and Monte Carlo simulations with the TRIM code. Average LET of particles incident on the cells at the center of the Petri dish was evaluated to be 120 keV microm(-1) at 59 mm from the source, and the average dose rate was 5.69 x 10 Gy s(-1), with +12% and -8% variations at the center and the edge, respectively. The irradiator has been successfully tested and used for several experiments involving 16-d exposure of human fibroblasts monolayers.