Lipowitz metal shielding thickness for dose reduction of 6–20 MeV electrons

The relative dose reduction by Lipowitz metal of 6 to 20 MeV electrons from a Varian Associates Clinac–20 linear accelerator has been measured using a parallel plate thin wall ionization chamber. Metal thicknesses required for a 5% attenuation level for a 10×10 cm² field are as follows: 6 MeV–2.3 mm, 9 MeV–4.4 mm, 12 MeV–8.5 mm, 16 MeV–18.0 mm, 20 MeV–25.0 mm.