Production of extremely thin plastic films of large area for gas-filled detectors

The production and investigation of properties of 60 × 15 cm² Formvar foils with mass area densities from 1 to 150 μgcm^-2 is described. The foils are used both as entrance windows of a large ionization chamber and coated with a thin gold layer, as cathode foils of a parallel-plate avalanche counter. The production technique is based on the method of lacquering a surface of distilled water with a solution of Formvar in 1,2-dichlorethane. The thicknesses of the foils are determined with various methods. Their rupture strength and gas permeability are investigated. The differential energy loss as well as the energy-loss straggling in these foils are measured for ¹⁶O-ions using the 4 MV tandem accelerator in Bochum.