PARENT SESSION
1:30 PM to 3:30 PM
Wednesday, April 24, 2002
Poster Session 30 Bystander Effects
Room: Nevada Exhibition Center

(P35-340) A new low-fluence alpha-particle irradiator for radiobiological applications.

de Toledo, Sonia^*,1, Azzam, Edouard¹, Howell, Roger¹, ¹ New Jersey Medical School, Newark, NJ

ABSTRACT-
A new multi-port alpha particle irradiator, designed to facilitate the study of bystander effects in monolayer cultures, has been constructed. The irradiator consists of 4 individual planar ²⁴¹Am alpha particle sources that are housed inside a helium-filled Plexiglas box. Americium-241 emits 5.4 MeV alpha particles. Three of the radioactive sources consist of 0.540 mCi (60 mCi/in²) each of ²⁴¹Am oxide foil. The fourth source, used to produce higher dose-rates, consists of 13.5 mCi (1500 mCi/in²). 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 mm thick mylar exit windows on turntables rotated at 65 rpm. 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 that moves its table in an orbit of 0.75 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. Opening and closing of the shutters is controlled with a high precision timer. The latter allows irradiation of the monolayer over times ranging from 0.01 s to 20 min. The specially designed stainless steel mylar-bottomed dishes are placed on an adaptor on the shutter. The energy spectrum of the alpha particles that strike the cells is measured with a particle detector connected to a multichannel analyzer. This spectrum is used in turn to determine the LET distribution of the particles. Preliminary experiments indicate that the irradiator is well-suited to study bystander effects in monolayer cultures.

KEYWORDS: bystander effects, alpha particle, irradiator, americium-241