Microdosimetry and chromosome aberrations: effects of 230 keV neutrons on Vicia faba chromosomes.

Physical energy deposition events have been related to sub-nuclear cytological events (chromosomal changes) in metaphases sequentially accumulated from the latter part of the cell cycle of Vicia faba. 230 keV neutrons produce about 0.4 recoil protons per late interphase nucleus per rad with the majority of protons traveling 1 to 2 microns from their origin, depositing energy at around 90 keV per micron. The frequency of induced abberrations is basically linear with dose, though varying through consecutive cell sampling periods because of differential induced mitotic delay. Distributions of chromosomal aberrations and total cytological events are overdispersed in relation to the Poisson distribution indicating that some proton recoils produce multiple events. When gaps and aberrations within chromosomes and multiple aberrations between chromosomes, are considered as discrete events, distributions follow Poisson expectations. About 40% of proton recoils result in observable cytological change. The highly energetic proton recoils (approximately 90 keV per micron) which can induce multiple events are the ones most likely to produce effects which result in cell death. The sphere of influence of the proton recoils is probably adequately estimated from their range (approximately 1 to 2 micron) since it seems compatible with the spatial proximity of the initial components of the resultant chromosome aberrations.