Limits imposed by ionizing radiation on the long-term survival of trapped bacterial spores: beta radiation

Abstract

Purpose : A model is presented for determining the survival time TF of a fraction F of a population of bacterial spores trapped within a fluid inclusion and subject to genetic damage from beta radiation. Methods : The limiting factor to survival is the production of double-strand breaks (DSB) in the DNA resulting from singletrack cleaving and from the cumulative effects of single-strand breaks (SSB) induced by the presence of ionizing radiation in the environment. The model considers the probability that radicals and ions formed by the passage of high-energy particles will interact with a DNA molecule and induce damage. Results : The survival time T for a fraction F of a trapped population is a weak function F of both F and the length L in base pairs of the genome. For irradiation due to a beta source trapped with the spores within the inclusion, the survival time is also inversely proportional to the concentration of the radionuclide, the dominant factor in limiting survival time. Conclusions : The predictions of the model are consistent with measured DSB formation rates, the observed survival of trapped spores over time periods as long as 250Ma, and track structure models which address low physical dose rates.