This work describes multiple experimental improvements for measuring absolute cross sections of DNA damage induced by low-energy electrons (LEE) in nanometer-thick films in vacuum. Measurements of such cross sections are particularly sensitive to film thickness and uniformity. Using atomic force microscopy (AFM) in 70% ethanol, we present a novel and effective method to determine plasmid DNA film thickness and uniformity that combines height histograms and force-distance curves. We also investigate film deposition with DNA intercalated with 1,3-diaminopropane (Dap) on tantalum-coated substrates as a convenient and cost-effective alternative to the previously-used graphite substrate. The tantalum substrate permits deposition of films very similar to those formed on graphite. Using these refinements and further optimizations of the experimental procedure, we measure an absolute cross section of (4.7 ± 1.5) x10-14 cm 2 for conformational damage to a 3197 base-pair plasmid induced by 10 eV electrons, which we believe should be considered as a reference value. I. INTRODUCTION: Ionizing radiation is widely employed in cancer therapy (e.g., in radiotherapy [1, 2], brachytherapy [3] and targeted radionuclide therapy (TRT) [4,5]), as well as in medical diagnostic imaging. In these applications, the radiation dose given to the patient should be known and controlled. In conventional cancer treatments, calculations of the absorbed dose rely on scattering cross sections (CSs) of the primary high-energy radiation. In more sophisticated treatments, such as therapies combining radiation