A Multi-port Low-Fluence Alpha-Particle Irradiator: Fabrication Testing and Benchmark Radiobiological Studies

摘要

A new multi-port irradiator, designed to facilitate the study of the effects of low fluences of α particles on monolayer cultures, has been developed. The irradiator consists of four individual planar ²⁴¹Am α-particle sources that are housed inside a helium-filled Lucite chamber. Three of the radioactive sources consist of 20 MBq of ²⁴¹Am dioxide foil. The fourth source, used to produce higher dose rates, has an activity of 500 MBq. The four sources are mounted on rotating turntables parallel to their respective 1.5-μm-thick Mylar exit windows. A stainless steel honeycomb collimator is placed between the four sources and their exit windows by a cantilever attachment to the platform of an orbital shaker that moves its table in an orbit of 2 cm. Each exit window is equipped with a beam delimiter to optimize the uniformity of the beam and with a high-precision electronic shutter. Opening and closing of the shutters is controlled with a high-precision timer. Custom-designed stainless steel Mylar-bottomed culture dishes are placed on an adapter on the shutter. The α particles that strike the cells have a mean energy of 2.9 MeV. The corresponding LET distribution of the particles has a mean value of 132 keV/μm. Clonogenic cell survival experiments with AG1522 human fibroblasts indicate that the RBE of the α particles compared to ¹³⁷Cs γ rays is about 7.6 for this biological end point.