Young inflorescences of Tradescantia clone 02 were irradiated with 3.9-GeV nitrogen ions from the Princeton Particle Accelerator. The inflorescences were irradiated at several positions along the nitrogen depth-dose curve. Petals and stamen hairs were scored for pink mutations. The slopes of the dose-response curves from each position on the depth-dose curve were linear with dose. RBE was found to decrease with increasing dose. Maximum RBE values, relative to 250-kVp x-rays were determined at each position. The lowest RBE (3.8) occurred upstream in the beam on the pre-Bragg plateau. An RBE max of 5.6 was found behind the Bragg peak. In two experiments the RBE max was found to be 14.3 and 15.6 at the Bragg peak, while a higher RBE (18.5) was found 2 mm in front of the Bragg peak. This latter effect was attributed to possible excess ionization density at the Bragg peak.

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