<p> Alpha Particle Irradiator Facility</p><p>An alpha particle irradiator, designed to irradiate cells in monolayer cultures, has been assembled here at the New Jersey Medical School (NJMS). The fundamental design is based on an irradiator designed by Metting et al. (Health Phys. 68: 710-715, 1995). The NJMS irradiator consists of 4 individual planar 241Am alpha particle sources (NRD Inc., Buffalo, NY) that are housed inside a helium-filled Plexiglas box (21 x 16 x 8 in). Three of the radioactive sources consist of 0.540 mCi (60 Ci/in2) each of 241Am oxide foil. The fourth source, used to produce higher dose-rates, consists of 13.5 mCi (1500 Ci/in2). Americium-241 emits alpha particles with almost the same energy as 238Pu, the source used in the original Metting design. The foil is comprised of a silver overcoat and undercoat, silver plus 241Am oxide active layer, and 0.006 in thick silver backing that is welded and rolled. The foil was fabricated with the active layer centered between 2 inactive margins. The result is a planar 3 x 3 in. source that emits 4.7 MeV alpha particles (0.7 MeV FWHM). The four sources are mounted parallel to their respective 1.5 m thick mylar exit windows on turntables rotated at 65 rpm. (Magna-Torc motor, Hansen Corporation). The turntables are included to ensure uniform irradiation of the mylar-bottomed cell culture dishes. A stainless-steel honeycomb collimator is placed between the three sources and their exit windows by a cantilever attachment to the platform of an orbital shaker (Roto Mix, Thermolyne) that moves its table in an orbit of ¾ in. During the irradiation the collimator is moved at 150 orbits per minute. Each exit window is equipped with a beam delimiter to optimize the uniformity of the beam and a high precision electronic Copal specialty shutter (model DC-392). Opening and closing of the shutters is controlled with a high precision timer (Logotron LGT 12 DC, Entrelec). The specially designed stainless steel mylar-bottomed dishes are placed on an adaptor on the shutter. The latter allows irradiation of the monolayer over times ranging from 0.01 s to 20 min. </p>