Quantitative analysis of dose dependent DNA fragmentation in dry pBR322 plasmid using long read sequencing and Monte Carlo simulations.

Exposure to ionizing radiation can induce genetic aberrations via unrepaired DNA strand breaks. To investigate quantitatively the dose-effect relationship at the molecular level, we irradiated dry pBR322 plasmid DNA with 3 MeV protons and assessed fragmentation yields at different radiation doses using long-read sequencing from Oxford Nanopore Technologies. This technology applied to a reference DNA model revealed dose-dependent fragmentation, as evidenced by read length distributions, showing no discernible radiation sensitivity in specific genetic sequences. In addition, we propose a method for directly measuring the single-strand break (SSB) yield. Furthermore, through a comparative study with a collection of previous works on dry DNA irradiation, we show that the irradiation protocol leads to biases in the definition of ionizing sources. We support this scenario by discussing the size distributions of nanopore sequencing reads in the light of Geant4 and Geant4-DNA simulation toolkit predictions. We show that integrating long-read sequencing technologies with advanced Monte Carlo simulations paves a promising path toward advancing our comprehension and prediction of radiation-induced DNA fragmentation.

Role of the pre-plasma on electron beam currents from a biased laser-plasma.

We are investigating laser-plasmas produced in the interaction of a 1 J 9 ns Nd:YAG laser with a solid metal target as a source of electrons. An electron beam pulsed at the laser repetition rate is produced by biasing the target and making the plasma expand in an electric field. In this paper, we focus on the measured beam currents and charge surface distribution of the beam. The peak beam currents are much higher than what is given by a simplified toy model based on the Child-Langmuir limit in a vacuum and the charge surface distributions are inhomogeneous. Both these observations are explained by the presence of a positive preplasma expanding ahead of the laser-plasma front edge.