RADIOBIOLOGY OF ALPHA-PARTICLES .2. DOSIMETRY OF LOW-ENERGY ALPHA-PARTICLES USING PARALLEL-PLATE IONIZATION CHAMBERS AND A SURFACE-BARRIER DETECTOR

Three small parallel-plate ionization chambers were developed for measuring dose rates, of primarily low-energy α particles in the energy range 0.4-3.5 MeV, at a defined cell-Mylar interface. Spectral energy distributions of these α particles were also measured at the same position using a specially designed small-area silicon surface barrier detector. Dose rates were derived from the spectral distributions and compared with those derived from the ionization chambers. Different α-particle energies were obtained using a 144-MBq 238Pu collimated source and a variety of Mylar moderator foils of different thicknesses. These measurements, extended to mean α-particle energies as low as 0.4 MeV, will enable us to correlate radiobiological data with effects of α particles terminating in different regions of cell nuclei.